Reorganize the scan-minor-copy/scan.h header files a bit. Move the nursery copying...

[mono-project.git] / mono / mini / mini-gc.c

/*
 * mini-gc.c: GC interface for the mono JIT
 *
 * Author:
 *   Zoltan Varga (vargaz@gmail.com)
 *
 * Copyright 2009 Novell, Inc (http://www.novell.com)
 * Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
 */

#include "config.h"
#include "mini-gc.h"
#include <mono/metadata/gc-internal.h>

//#if 0
#if defined(MONO_ARCH_GC_MAPS_SUPPORTED)

#include <mono/metadata/gc-internal.h>
#include <mono/utils/mono-counters.h>

#if SIZEOF_VOID_P == 4
typedef guint32 mword;
#else
typedef guint64 mword;
#endif

#define SIZEOF_SLOT ((int)sizeof (mgreg_t))

#define GC_BITS_PER_WORD (sizeof (mword) * 8)

/* Contains state needed by the GC Map construction code */
typedef struct {
        /*
         * This contains information about stack slots initialized in the prolog, encoded using
         * (slot_index << 16) | slot_type. The slot_index is relative to the CFA, i.e. 0
         * means cfa+0, 1 means cfa-4/8, etc.
         */
        GSList *stack_slots_from_cfa;
        /* Same for stack slots relative to the frame pointer */
        GSList *stack_slots_from_fp;

        /* Number of slots in the map */
        int nslots;
        /* The number of registers in the map */
        int nregs;
        /* Min and Max offsets of the stack frame relative to fp */
        int min_offset, max_offset;
        /* Same for the locals area */
        int locals_min_offset, locals_max_offset;

        /* The call sites where this frame can be stopped during GC */
        GCCallSite **callsites;
        /* The number of call sites */
        int ncallsites;

        /*
         * The width of the stack bitmaps in bytes. This is not equal to the bitmap width at
     * runtime, since it includes columns which are 0.
         */
        int stack_bitmap_width;
        /* 
         * A bitmap whose width equals nslots, and whose height equals ncallsites.
         * The bitmap contains a 1 if the corresponding stack slot has type SLOT_REF at the
         * given callsite.
         */
        guint8 *stack_ref_bitmap;
        /* Same for SLOT_PIN */
        guint8 *stack_pin_bitmap;

        /*
         * Similar bitmaps for registers. These have width MONO_MAX_IREGS in bits.
         */
        int reg_bitmap_width;
        guint8 *reg_ref_bitmap;
        guint8 *reg_pin_bitmap;
} MonoCompileGC;

#define ALIGN_TO(val,align) ((((mgreg_t)val) + ((align) - 1)) & ~((align) - 1))

#undef DEBUG

#if 0
/* We don't support debug levels, its all-or-nothing */
#define DEBUG(s) do { s; fflush (logfile); } while (0)
#define DEBUG_ENABLED 1
#else
#define DEBUG(s)
#endif

#ifdef DEBUG_ENABLED
//#if 1
#define DEBUG_PRECISE(s) do { s; } while (0)
#define DEBUG_PRECISE_ENABLED
#else
#define DEBUG_PRECISE(s)
#endif

/*
 * Contains information collected during the conservative stack marking pass,
 * used during the precise pass. This helps to avoid doing a stack walk twice, which
 * is expensive.
 */
typedef struct {
        guint8 *bitmap;
        int nslots;
    int frame_start_offset;
        int nreg_locations;
        /* Relative to stack_start */
        int reg_locations [MONO_MAX_IREGS];
#ifdef DEBUG_PRECISE_ENABLED
        MonoJitInfo *ji;
        gpointer fp;
        int regs [MONO_MAX_IREGS];
#endif
} FrameInfo;

/* Max number of frames stored in the TLS data */
#define MAX_FRAMES 50

/*
 * Per-thread data kept by this module. This is stored in the GC and passed to us as
 * parameters, instead of being stored in a TLS variable, since during a collection,
 * only the collection thread is active.
 */
typedef struct {
        MonoThreadUnwindState unwind_state;
        MonoThreadInfo *info;
        /* For debugging */
        mgreg_t tid;
        gpointer ref_to_track;
        /* Number of frames collected during the !precise pass */
        int nframes;
        FrameInfo frames [MAX_FRAMES];
} TlsData;

/* These are constant so don't store them in the GC Maps */
/* Number of registers stored in gc maps */
#define NREGS MONO_MAX_IREGS

/* 
 * The GC Map itself.
 * Contains information needed to mark a stack frame.
 * This is a transient structure, created from a compressed representation on-demand.
 */
typedef struct {
        /*
         * The offsets of the GC tracked area inside the stack frame relative to the frame pointer.
         * This includes memory which is NOREF thus doesn't need GC maps.
         */
        int start_offset;
        int end_offset;
        /*
         * The offset relative to frame_offset where the the memory described by the GC maps
         * begins.
         */
        int map_offset;
        /* The number of stack slots in the map */
        int nslots;
        /* The frame pointer register */
        guint8 frame_reg;
        /* The size of each callsite table entry */
        guint8 callsite_entry_size;
        guint has_pin_slots : 1;
        guint has_ref_slots : 1;
        guint has_ref_regs : 1;
        guint has_pin_regs : 1;

        /* The offsets below are into an external bitmaps array */

        /* 
         * A bitmap whose width is equal to bitmap_width, and whose height is equal to ncallsites.
         * The bitmap contains a 1 if the corresponding stack slot has type SLOT_REF at the
         * given callsite.
         */
        guint32 stack_ref_bitmap_offset;
        /*
         * Same for SLOT_PIN. It is possible that the same bit is set in both bitmaps at
     * different callsites, if the slot starts out as PIN, and later changes to REF.
         */
        guint32 stack_pin_bitmap_offset;

        /*
         * Corresponding bitmaps for registers
         * These have width equal to the number of bits set in reg_ref_mask/reg_pin_mask.
         * FIXME: Merge these with the normal bitmaps, i.e. reserve the first x slots for them ?
         */
        guint32 reg_pin_bitmap_offset;
        guint32 reg_ref_bitmap_offset;

        guint32 used_int_regs, reg_ref_mask, reg_pin_mask;

        /* The number of bits set in the two masks above */
        guint8 nref_regs, npin_regs;

        /*
         * A bit array marking slots which contain refs.
         * This is used only for debugging.
         */
        //guint8 *ref_slots;

        /* Callsite offsets */
        /* These can take up a lot of space, so encode them compactly */
        union {
                guint8 *offsets8;
                guint16 *offsets16;
                guint32 *offsets32;
        } callsites;
        int ncallsites;
} GCMap;

/*
 * A compressed version of GCMap. This is what gets stored in MonoJitInfo.
 */
typedef struct {
        //guint8 *ref_slots;
        //guint8 encoded_size;

        /*
         * The arrays below are embedded after the struct.
         * Their address needs to be computed.
         */

        /* The fixed fields of the GCMap encoded using LEB128 */
        guint8 encoded [MONO_ZERO_LEN_ARRAY];

        /* An array of ncallsites entries, each entry is callsite_entry_size bytes long */
        guint8 callsites [MONO_ZERO_LEN_ARRAY];

        /* The GC bitmaps */
        guint8 bitmaps [MONO_ZERO_LEN_ARRAY];
} GCEncodedMap;

static int precise_frame_count [2], precise_frame_limit = -1;
static gboolean precise_frame_limit_inited;

/* Stats */
typedef struct {
        int scanned_stacks;
        int scanned;
        int scanned_precisely;
        int scanned_conservatively;
        int scanned_registers;
        int scanned_native;
        int scanned_other;
        
        int all_slots;
        int noref_slots;
        int ref_slots;
        int pin_slots;

        int gc_maps_size;
        int gc_callsites_size;
        int gc_callsites8_size;
        int gc_callsites16_size;
        int gc_callsites32_size;
        int gc_bitmaps_size;
        int gc_map_struct_size;
        int tlsdata_size;
} JITGCStats;

static JITGCStats stats;

static FILE *logfile;

static gboolean enable_gc_maps_for_aot;

void
mini_gc_enable_gc_maps_for_aot (void)
{
        enable_gc_maps_for_aot = TRUE;
}

// FIXME: Move these to a shared place

static inline void
encode_uleb128 (guint32 value, guint8 *buf, guint8 **endbuf)
{
        guint8 *p = buf;

        do {
                guint8 b = value & 0x7f;
                value >>= 7;
                if (value != 0) /* more bytes to come */
                        b |= 0x80;
                *p ++ = b;
        } while (value);

        *endbuf = p;
}

static G_GNUC_UNUSED void
encode_sleb128 (gint32 value, guint8 *buf, guint8 **endbuf)
{
        gboolean more = 1;
        gboolean negative = (value < 0);
        guint32 size = 32;
        guint8 byte;
        guint8 *p = buf;

        while (more) {
                byte = value & 0x7f;
                value >>= 7;
                /* the following is unnecessary if the
                 * implementation of >>= uses an arithmetic rather
                 * than logical shift for a signed left operand
                 */
                if (negative)
                        /* sign extend */
                        value |= - (1 <<(size - 7));
                /* sign bit of byte is second high order bit (0x40) */
                if ((value == 0 && !(byte & 0x40)) ||
                        (value == -1 && (byte & 0x40)))
                        more = 0;
                else
                        byte |= 0x80;
                *p ++= byte;
        }

        *endbuf = p;
}

static inline guint32
decode_uleb128 (guint8 *buf, guint8 **endbuf)
{
        guint8 *p = buf;
        guint32 res = 0;
        int shift = 0;

        while (TRUE) {
                guint8 b = *p;
                p ++;

                res = res | (((int)(b & 0x7f)) << shift);
                if (!(b & 0x80))
                        break;
                shift += 7;
        }

        *endbuf = p;

        return res;
}

static inline gint32
decode_sleb128 (guint8 *buf, guint8 **endbuf)
{
        guint8 *p = buf;
        gint32 res = 0;
        int shift = 0;

        while (TRUE) {
                guint8 b = *p;
                p ++;

                res = res | (((int)(b & 0x7f)) << shift);
                shift += 7;
                if (!(b & 0x80)) {
                        if (shift < 32 && (b & 0x40))
                                res |= - (1 << shift);
                        break;
                }
        }

        *endbuf = p;

        return res;
}

static int
encode_frame_reg (int frame_reg)
{
#ifdef TARGET_AMD64
        if (frame_reg == AMD64_RSP)
                return 0;
        else if (frame_reg == AMD64_RBP)
                return 1;
#elif defined(TARGET_X86)
        if (frame_reg == X86_EBP)
                return 0;
        else if (frame_reg == X86_ESP)
                return 1;
#elif defined(TARGET_ARM)
        if (frame_reg == ARMREG_SP)
                return 0;
        else if (frame_reg == ARMREG_FP)
                return 1;
#elif defined(TARGET_S390X)
        if (frame_reg == S390_SP)
                return 0;
        else if (frame_reg == S390_FP)
                return 1;
#else
        NOT_IMPLEMENTED;
#endif
        g_assert_not_reached ();
        return -1;
}

static int
decode_frame_reg (int encoded)
{
#ifdef TARGET_AMD64
        if (encoded == 0)
                return AMD64_RSP;
        else if (encoded == 1)
                return AMD64_RBP;
#elif defined(TARGET_X86)
        if (encoded == 0)
                return X86_EBP;
        else if (encoded == 1)
                return X86_ESP;
#elif defined(TARGET_ARM)
        if (encoded == 0)
                return ARMREG_SP;
        else if (encoded == 1)
                return ARMREG_FP;
#elif defined(TARGET_S390X)
        if (encoded == 0)
                return S390_SP;
        else if (encoded == 1)
                return S390_FP;
#else
        NOT_IMPLEMENTED;
#endif
        g_assert_not_reached ();
        return -1;
}

#ifdef TARGET_AMD64
#ifdef HOST_WIN32
static int callee_saved_regs [] = { AMD64_RBP, AMD64_RBX, AMD64_R12, AMD64_R13, AMD64_R14, AMD64_R15, AMD64_RDI, AMD64_RSI };
#else
static int callee_saved_regs [] = { AMD64_RBP, AMD64_RBX, AMD64_R12, AMD64_R13, AMD64_R14, AMD64_R15 };
#endif
#elif defined(TARGET_X86)
static int callee_saved_regs [] = { X86_EBX, X86_ESI, X86_EDI };
#elif defined(TARGET_ARM)
static int callee_saved_regs [] = { ARMREG_V1, ARMREG_V2, ARMREG_V3, ARMREG_V4, ARMREG_V5, ARMREG_V7, ARMREG_FP };
#elif defined(TARGET_S390X)
static int callee_saved_regs [] = { s390_r6, s390_r7, s390_r8, s390_r9, s390_r10, s390_r11, s390_r12, s390_r13, s390_r14 };
#endif

static guint32
encode_regmask (guint32 regmask)
{
        int i;
        guint32 res;

        res = 0;
        for (i = 0; i < sizeof (callee_saved_regs) / sizeof (int); ++i) {
                if (regmask & (1 << callee_saved_regs [i])) {
                        res |= (1 << i);
                        regmask -= (1 << callee_saved_regs [i]);
                }
        }
        g_assert (regmask == 0);
        return res;
}

static guint32
decode_regmask (guint32 regmask)
{
        int i;
        guint32 res;

        res = 0;
        for (i = 0; i < sizeof (callee_saved_regs) / sizeof (int); ++i)
                if (regmask & (1 << i))
                        res |= (1 << callee_saved_regs [i]);
        return res;
}

/*
 * encode_gc_map:
 *
 *   Encode the fixed fields of MAP into a buffer pointed to by BUF.
 */
static void
encode_gc_map (GCMap *map, guint8 *buf, guint8 **endbuf)
{
        guint32 flags, freg;

        encode_sleb128 (map->start_offset / SIZEOF_SLOT, buf, &buf);
        encode_sleb128 (map->end_offset / SIZEOF_SLOT, buf, &buf);
        encode_sleb128 (map->map_offset / SIZEOF_SLOT, buf, &buf);
        encode_uleb128 (map->nslots, buf, &buf);
        g_assert (map->callsite_entry_size <= 4);
        freg = encode_frame_reg (map->frame_reg);
        g_assert (freg < 2);
        flags = (map->has_ref_slots ? 1 : 0) | (map->has_pin_slots ? 2 : 0) | (map->has_ref_regs ? 4 : 0) | (map->has_pin_regs ? 8 : 0) | ((map->callsite_entry_size - 1) << 4) | (freg << 6);
        encode_uleb128 (flags, buf, &buf);
        encode_uleb128 (encode_regmask (map->used_int_regs), buf, &buf);
        if (map->has_ref_regs)
                encode_uleb128 (encode_regmask (map->reg_ref_mask), buf, &buf);
        if (map->has_pin_regs)
                encode_uleb128 (encode_regmask (map->reg_pin_mask), buf, &buf);
        encode_uleb128 (map->ncallsites, buf, &buf);

        *endbuf = buf;
}       

/*
 * decode_gc_map:
 *
 *   Decode the encoded GC map representation in BUF and store the result into MAP.
 */
static void
decode_gc_map (guint8 *buf, GCMap *map, guint8 **endbuf)
{
        guint32 flags;
        int stack_bitmap_size, reg_ref_bitmap_size, reg_pin_bitmap_size, offset, freg;
        int i, n;

        map->start_offset = decode_sleb128 (buf, &buf) * SIZEOF_SLOT;
        map->end_offset = decode_sleb128 (buf, &buf) * SIZEOF_SLOT;
        map->map_offset = decode_sleb128 (buf, &buf) * SIZEOF_SLOT;
        map->nslots = decode_uleb128 (buf, &buf);
        flags = decode_uleb128 (buf, &buf);
        map->has_ref_slots = (flags & 1) ? 1 : 0;
        map->has_pin_slots = (flags & 2) ? 1 : 0;
        map->has_ref_regs = (flags & 4) ? 1 : 0;
        map->has_pin_regs = (flags & 8) ? 1 : 0;
        map->callsite_entry_size = ((flags >> 4) & 0x3) + 1;
        freg = flags >> 6;
        map->frame_reg = decode_frame_reg (freg);
        map->used_int_regs = decode_regmask (decode_uleb128 (buf, &buf));
        if (map->has_ref_regs) {
                map->reg_ref_mask = decode_regmask (decode_uleb128 (buf, &buf));
                n = 0;
                for (i = 0; i < NREGS; ++i)
                        if (map->reg_ref_mask & (1 << i))
                                n ++;
                map->nref_regs = n;
        }
        if (map->has_pin_regs) {
                map->reg_pin_mask = decode_regmask (decode_uleb128 (buf, &buf));
                n = 0;
                for (i = 0; i < NREGS; ++i)
                        if (map->reg_pin_mask & (1 << i))
                                n ++;
                map->npin_regs = n;
        }
        map->ncallsites = decode_uleb128 (buf, &buf);

        stack_bitmap_size = (ALIGN_TO (map->nslots, 8) / 8) * map->ncallsites;
        reg_ref_bitmap_size = (ALIGN_TO (map->nref_regs, 8) / 8) * map->ncallsites;
        reg_pin_bitmap_size = (ALIGN_TO (map->npin_regs, 8) / 8) * map->ncallsites;
        offset = 0;
        map->stack_ref_bitmap_offset = offset;
        if (map->has_ref_slots)
                offset += stack_bitmap_size;
        map->stack_pin_bitmap_offset = offset;
        if (map->has_pin_slots)
                offset += stack_bitmap_size;
        map->reg_ref_bitmap_offset = offset;
        if (map->has_ref_regs)
                offset += reg_ref_bitmap_size;
        map->reg_pin_bitmap_offset = offset;
        if (map->has_pin_regs)
                offset += reg_pin_bitmap_size;

        *endbuf = buf;
}

static gpointer
thread_attach_func (void)
{
        TlsData *tls;

        tls = g_new0 (TlsData, 1);
        tls->tid = GetCurrentThreadId ();
        tls->info = mono_thread_info_current ();
        stats.tlsdata_size += sizeof (TlsData);

        return tls;
}

static void
thread_detach_func (gpointer user_data)
{
        TlsData *tls = user_data;

        g_free (tls);
}

static void
thread_suspend_func (gpointer user_data, void *sigctx, MonoContext *ctx)
{
        TlsData *tls = user_data;

        if (!tls) {
                /* Happens during startup */
                tls->unwind_state.valid = FALSE;
                return;
        }

        if (tls->tid != GetCurrentThreadId ()) {
                /* Happens on osx because threads are not suspended using signals */
                gboolean res;

                g_assert (tls->info);
                res = mono_thread_state_init_from_handle (&tls->unwind_state, (MonoNativeThreadId)tls->tid, tls->info->native_handle);
        } else {
                tls->unwind_state.unwind_data [MONO_UNWIND_DATA_LMF] = mono_get_lmf ();
                if (sigctx) {
                        mono_arch_sigctx_to_monoctx (sigctx, &tls->unwind_state.ctx);
                        tls->unwind_state.valid = TRUE;
                } else if (ctx) {
                        memcpy (&tls->unwind_state.ctx, ctx, sizeof (MonoContext));
                        tls->unwind_state.valid = TRUE;
                } else {
                        tls->unwind_state.valid = FALSE;
                }
                tls->unwind_state.unwind_data [MONO_UNWIND_DATA_JIT_TLS] = mono_native_tls_get_value (mono_jit_tls_id);
                tls->unwind_state.unwind_data [MONO_UNWIND_DATA_DOMAIN] = mono_domain_get ();
        }

        if (!tls->unwind_state.unwind_data [MONO_UNWIND_DATA_DOMAIN]) {
                /* Happens during startup */
                tls->unwind_state.valid = FALSE;
                return;
        }
}

#define DEAD_REF ((gpointer)(gssize)0x2a2a2a2a2a2a2a2aULL)

static inline void
set_bit (guint8 *bitmap, int width, int y, int x)
{
        bitmap [(width * y) + (x / 8)] |= (1 << (x % 8));
}

static inline void
clear_bit (guint8 *bitmap, int width, int y, int x)
{
        bitmap [(width * y) + (x / 8)] &= ~(1 << (x % 8));
}

static inline int
get_bit (guint8 *bitmap, int width, int y, int x)
{
        return bitmap [(width * y) + (x / 8)] & (1 << (x % 8));
}

static const char*
slot_type_to_string (GCSlotType type)
{
        switch (type) {
        case SLOT_REF:
                return "ref";
        case SLOT_NOREF:
                return "noref";
        case SLOT_PIN:
                return "pin";
        default:
                g_assert_not_reached ();
                return NULL;
        }
}

static inline mgreg_t
get_frame_pointer (MonoContext *ctx, int frame_reg)
{
#if defined(TARGET_AMD64)
                if (frame_reg == AMD64_RSP)
                        return ctx->rsp;
                else if (frame_reg == AMD64_RBP)
                        return ctx->rbp;
#elif defined(TARGET_X86)
                if (frame_reg == X86_ESP)
                        return ctx->esp;
                else if (frame_reg == X86_EBP)
                        return ctx->ebp;
#elif defined(TARGET_ARM)
                if (frame_reg == ARMREG_SP)
                        return (mgreg_t)MONO_CONTEXT_GET_SP (ctx);
                else if (frame_reg == ARMREG_FP)
                        return (mgreg_t)MONO_CONTEXT_GET_BP (ctx);
#elif defined(TARGET_S390X)
                if (frame_reg == S390_SP)
                        return (mgreg_t)MONO_CONTEXT_GET_SP (ctx);
                else if (frame_reg == S390_FP)
                        return (mgreg_t)MONO_CONTEXT_GET_BP (ctx);
#endif
                g_assert_not_reached ();
                return 0;
}

/*
 * conservatively_pass:
 *
 *   Mark a thread stack conservatively and collect information needed by the precise pass.
 */
static void
conservative_pass (TlsData *tls, guint8 *stack_start, guint8 *stack_end)
{
        MonoJitInfo *ji;
        MonoContext ctx, new_ctx;
        MonoLMF *lmf;
        guint8 *stack_limit;
        gboolean last = TRUE;
        GCMap *map;
        GCMap map_tmp;
        GCEncodedMap *emap;
        guint8* fp, *p, *real_frame_start, *frame_start, *frame_end;
        int i, pc_offset, cindex, bitmap_width;
        int scanned = 0, scanned_precisely, scanned_conservatively, scanned_registers;
        gboolean res;
        StackFrameInfo frame;
        mgreg_t *reg_locations [MONO_MAX_IREGS];
        mgreg_t *new_reg_locations [MONO_MAX_IREGS];
        guint8 *bitmaps;
        FrameInfo *fi;
        guint32 precise_regmask;

        if (tls) {
                tls->nframes = 0;
                tls->ref_to_track = NULL;
        }

        /* tls == NULL can happen during startup */
        if (mono_thread_internal_current () == NULL || !tls) {
                mono_gc_conservatively_scan_area (stack_start, stack_end);
                stats.scanned_stacks += stack_end - stack_start;
                return;
        }

        lmf = tls->unwind_state.unwind_data [MONO_UNWIND_DATA_LMF];
        frame.domain = NULL;

        /* Number of bytes scanned based on GC map data */
        scanned = 0;
        /* Number of bytes scanned precisely based on GC map data */
        scanned_precisely = 0;
        /* Number of bytes scanned conservatively based on GC map data */
        scanned_conservatively = 0;
        /* Number of bytes scanned conservatively in register save areas */
        scanned_registers = 0;

        /* This is one past the last address which we have scanned */
        stack_limit = stack_start;

        if (!tls->unwind_state.valid)
                memset (&new_ctx, 0, sizeof (ctx));
        else
                memcpy (&new_ctx, &tls->unwind_state.ctx, sizeof (MonoContext));

        memset (reg_locations, 0, sizeof (reg_locations));
        memset (new_reg_locations, 0, sizeof (new_reg_locations));

        while (TRUE) {
                if (!tls->unwind_state.valid)
                        break;

                memcpy (&ctx, &new_ctx, sizeof (ctx));

                for (i = 0; i < MONO_MAX_IREGS; ++i) {
                        if (new_reg_locations [i]) {
                                /*
                                 * If the current frame saves the register, it means it might modify its
                                 * value, thus the old location might not contain the same value, so
                                 * we have to mark it conservatively.
                                 */
                                if (reg_locations [i]) {
                                        DEBUG (fprintf (logfile, "\tscan saved reg %s location %p.\n", mono_arch_regname (i), reg_locations [i]));
                                        mono_gc_conservatively_scan_area (reg_locations [i], (char*)reg_locations [i] + SIZEOF_SLOT);
                                        scanned_registers += SIZEOF_SLOT;
                                }

                                reg_locations [i] = new_reg_locations [i];

                                DEBUG (fprintf (logfile, "\treg %s is now at location %p.\n", mono_arch_regname (i), reg_locations [i]));
                        }
                }

                g_assert ((mgreg_t)stack_limit % SIZEOF_SLOT == 0);

                res = mono_find_jit_info_ext (frame.domain ? frame.domain : tls->unwind_state.unwind_data [MONO_UNWIND_DATA_DOMAIN], tls->unwind_state.unwind_data [MONO_UNWIND_DATA_JIT_TLS], NULL, &ctx, &new_ctx, NULL, &lmf, new_reg_locations, &frame);
                if (!res)
                        break;

                ji = frame.ji;

                if (frame.type == FRAME_TYPE_MANAGED_TO_NATIVE) {
                        /*
                         * These frames are problematic for several reasons:
                         * - they are unwound through an LMF, and we have no precise register tracking for those.
                         * - the LMF might not contain a precise ip, so we can't compute the call site.
                         * - the LMF only unwinds to the wrapper frame, so we get these methods twice.
                         */
                        DEBUG (fprintf (logfile, "Mark(0): <Managed-to-native transition>\n"));
                        for (i = 0; i < MONO_MAX_IREGS; ++i) {
                                if (reg_locations [i]) {
                                        DEBUG (fprintf (logfile, "\tscan saved reg %s location %p.\n", mono_arch_regname (i), reg_locations [i]));
                                        mono_gc_conservatively_scan_area (reg_locations [i], (char*)reg_locations [i] + SIZEOF_SLOT);
                                        scanned_registers += SIZEOF_SLOT;
                                }
                                reg_locations [i] = NULL;
                                new_reg_locations [i] = NULL;
                        }
                        ctx = new_ctx;
                        continue;
                }

                /* The last frame can be in any state so mark conservatively */
                if (last) {
                        if (ji) {
                                DEBUG (char *fname = mono_method_full_name (ji->method, TRUE); fprintf (logfile, "Mark(0): %s+0x%x (%p)\n", fname, pc_offset, (gpointer)MONO_CONTEXT_GET_IP (&ctx)); g_free (fname));
                        }
                        DEBUG (fprintf (logfile, "\t <Last frame>\n"));
                        last = FALSE;
                        /*
                         * new_reg_locations is not precise when a method is interrupted during its epilog, so clear it.
                         */
                        for (i = 0; i < MONO_MAX_IREGS; ++i) {
                                if (reg_locations [i]) {
                                        DEBUG (fprintf (logfile, "\tscan saved reg %s location %p.\n", mono_arch_regname (i), reg_locations [i]));
                                        mono_gc_conservatively_scan_area (reg_locations [i], (char*)reg_locations [i] + SIZEOF_SLOT);
                                        scanned_registers += SIZEOF_SLOT;
                                }
                                if (new_reg_locations [i]) {
                                        DEBUG (fprintf (logfile, "\tscan saved reg %s location %p.\n", mono_arch_regname (i), new_reg_locations [i]));
                                        mono_gc_conservatively_scan_area (new_reg_locations [i], (char*)new_reg_locations [i] + SIZEOF_SLOT);
                                        scanned_registers += SIZEOF_SLOT;
                                }
                                reg_locations [i] = NULL;
                                new_reg_locations [i] = NULL;
                        }
                        continue;
                }

                pc_offset = (guint8*)MONO_CONTEXT_GET_IP (&ctx) - (guint8*)ji->code_start;

                /* These frames are very problematic */
                if (ji->method->wrapper_type == MONO_WRAPPER_MANAGED_TO_NATIVE) {
                        DEBUG (char *fname = mono_method_full_name (ji->method, TRUE); fprintf (logfile, "Mark(0): %s+0x%x (%p)\n", fname, pc_offset, (gpointer)MONO_CONTEXT_GET_IP (&ctx)); g_free (fname));
                        DEBUG (fprintf (logfile, "\tSkip.\n"));
                        continue;
                }

                /* All the other frames are at a call site */

                if (tls->nframes == MAX_FRAMES) {
                        /* 
                         * Can't save information since the array is full. So scan the rest of the
                         * stack conservatively.
                         */
                        DEBUG (fprintf (logfile, "Mark (0): Frame stack full.\n"));
                        break;
                }

                /* Scan the frame of this method */

                /*
                 * A frame contains the following:
                 * - saved registers
                 * - saved args
                 * - locals
                 * - spill area
                 * - localloc-ed memory
                 */
                g_assert (pc_offset >= 0);

                emap = ji->gc_info;

                if (!emap) {
                        DEBUG (char *fname = mono_method_full_name (ji->method, TRUE); fprintf (logfile, "Mark(0): %s+0x%x (%p)\n", fname, pc_offset, (gpointer)MONO_CONTEXT_GET_IP (&ctx)); g_free (fname));
                        DEBUG (fprintf (logfile, "\tNo GC Map.\n"));
                        continue;
                }

                /* The embedded callsite table requires this */
                g_assert (((mgreg_t)emap % 4) == 0);

                /*
                 * Debugging aid to control the number of frames scanned precisely
                 */
                if (!precise_frame_limit_inited) {
                        if (getenv ("MONO_PRECISE_COUNT"))
                                precise_frame_limit = atoi (getenv ("MONO_PRECISE_COUNT"));
                        precise_frame_limit_inited = TRUE;
                }
                                
                if (precise_frame_limit != -1) {
                        if (precise_frame_count [FALSE] == precise_frame_limit)
                                printf ("LAST PRECISE FRAME: %s\n", mono_method_full_name (ji->method, TRUE));
                        if (precise_frame_count [FALSE] > precise_frame_limit)
                                continue;
                }
                precise_frame_count [FALSE] ++;

                /* Decode the encoded GC map */
                map = &map_tmp;
                memset (map, 0, sizeof (GCMap));
                decode_gc_map (&emap->encoded [0], map, &p);
                p = (guint8*)ALIGN_TO (p, map->callsite_entry_size);
                map->callsites.offsets8 = p;
                p += map->callsite_entry_size * map->ncallsites;
                bitmaps = p;

                fp = (guint8*)get_frame_pointer (&ctx, map->frame_reg);

                real_frame_start = fp + map->start_offset;
                frame_start = fp + map->start_offset + map->map_offset;
                frame_end = fp + map->end_offset;

                DEBUG (char *fname = mono_method_full_name (ji->method, TRUE); fprintf (logfile, "Mark(0): %s+0x%x (%p) limit=%p fp=%p frame=%p-%p (%d)\n", fname, pc_offset, (gpointer)MONO_CONTEXT_GET_IP (&ctx), stack_limit, fp, frame_start, frame_end, (int)(frame_end - frame_start)); g_free (fname));

                /* Find the callsite index */
                if (map->callsite_entry_size == 1) {
                        for (i = 0; i < map->ncallsites; ++i)
                                /* ip points inside the call instruction */
                                if (map->callsites.offsets8 [i] == pc_offset + 1)
                                        break;
                } else if (map->callsite_entry_size == 2) {
                        // FIXME: Use a binary search
                        for (i = 0; i < map->ncallsites; ++i)
                                /* ip points inside the call instruction */
                                if (map->callsites.offsets16 [i] == pc_offset + 1)
                                        break;
                } else {
                        // FIXME: Use a binary search
                        for (i = 0; i < map->ncallsites; ++i)
                                /* ip points inside the call instruction */
                                if (map->callsites.offsets32 [i] == pc_offset + 1)
                                        break;
                }
                if (i == map->ncallsites) {
                        printf ("Unable to find ip offset 0x%x in callsite list of %s.\n", pc_offset + 1, mono_method_full_name (ji->method, TRUE));
                        g_assert_not_reached ();
                }
                cindex = i;

                /* 
                 * This is not neccessary true on x86 because frames have a different size at each
                 * call site.
                 */
                //g_assert (real_frame_start >= stack_limit);

                if (real_frame_start > stack_limit) {
                        /* This scans the previously skipped frames as well */
                        DEBUG (fprintf (logfile, "\tscan area %p-%p (%d).\n", stack_limit, real_frame_start, (int)(real_frame_start - stack_limit)));
                        mono_gc_conservatively_scan_area (stack_limit, real_frame_start);
                        stats.scanned_other += real_frame_start - stack_limit;
                }

                /* Mark stack slots */
                if (map->has_pin_slots) {
                        int bitmap_width = ALIGN_TO (map->nslots, 8) / 8;
                        guint8 *pin_bitmap = &bitmaps [map->stack_pin_bitmap_offset + (bitmap_width * cindex)];
                        guint8 *p;
                        gboolean pinned;

                        p = frame_start;
                        for (i = 0; i < map->nslots; ++i) {
                                pinned = pin_bitmap [i / 8] & (1 << (i % 8));
                                if (pinned) {
                                        DEBUG (fprintf (logfile, "\tscan slot %s0x%x(fp)=%p.\n", (guint8*)p > (guint8*)fp ? "" : "-", ABS ((int)((gssize)p - (gssize)fp)), p));
                                        mono_gc_conservatively_scan_area (p, p + SIZEOF_SLOT);
                                        scanned_conservatively += SIZEOF_SLOT;
                                } else {
                                        scanned_precisely += SIZEOF_SLOT;
                                }
                                p += SIZEOF_SLOT;
                        }
                } else {
                        scanned_precisely += (map->nslots * SIZEOF_SLOT);
                }

                /* The area outside of start-end is NOREF */
                scanned_precisely += (map->end_offset - map->start_offset) - (map->nslots * SIZEOF_SLOT);

                /* Mark registers */
                precise_regmask = map->used_int_regs | (1 << map->frame_reg);
                if (map->has_pin_regs) {
                        int bitmap_width = ALIGN_TO (map->npin_regs, 8) / 8;
                        guint8 *pin_bitmap = &bitmaps [map->reg_pin_bitmap_offset + (bitmap_width * cindex)];
                        int bindex = 0;
                        for (i = 0; i < NREGS; ++i) {
                                if (!(map->used_int_regs & (1 << i)))
                                        continue;
                                
                                if (!(map->reg_pin_mask & (1 << i)))
                                        continue;

                                if (pin_bitmap [bindex / 8] & (1 << (bindex % 8))) {
                                        DEBUG (fprintf (logfile, "\treg %s saved at 0x%p is pinning.\n", mono_arch_regname (i), reg_locations [i]));
                                        precise_regmask &= ~(1 << i);
                                }
                                bindex ++;
                        }
                }

                scanned += map->end_offset - map->start_offset;

                g_assert (scanned == scanned_precisely + scanned_conservatively);

                stack_limit = frame_end;

                /* Save information for the precise pass */
                fi = &tls->frames [tls->nframes];
                fi->nslots = map->nslots;
                bitmap_width = ALIGN_TO (map->nslots, 8) / 8;
                if (map->has_ref_slots)
                        fi->bitmap = &bitmaps [map->stack_ref_bitmap_offset + (bitmap_width * cindex)];
                else
                        fi->bitmap = NULL;
                fi->frame_start_offset = frame_start - stack_start;
                fi->nreg_locations = 0;
                DEBUG_PRECISE (fi->ji = ji);
                DEBUG_PRECISE (fi->fp = fp);

                if (map->has_ref_regs) {
                        int bitmap_width = ALIGN_TO (map->nref_regs, 8) / 8;
                        guint8 *ref_bitmap = &bitmaps [map->reg_ref_bitmap_offset + (bitmap_width * cindex)];
                        int bindex = 0;
                        for (i = 0; i < NREGS; ++i) {
                                if (!(map->reg_ref_mask & (1 << i)))
                                        continue;

                                if (reg_locations [i] && (ref_bitmap [bindex / 8] & (1 << (bindex % 8)))) {
                                        DEBUG_PRECISE (fi->regs [fi->nreg_locations] = i);
                                        DEBUG (fprintf (logfile, "\treg %s saved at 0x%p is ref.\n", mono_arch_regname (i), reg_locations [i]));
                                        fi->reg_locations [fi->nreg_locations] = (guint8*)reg_locations [i] - stack_start;
                                        fi->nreg_locations ++;
                                }
                                bindex ++;
                        }
                }

                /*
                 * Clear locations of precisely tracked registers.
                 */
                if (precise_regmask) {
                        for (i = 0; i < NREGS; ++i) {
                                if (precise_regmask & (1 << i)) {
                                        /*
                                         * The method uses this register, and we have precise info for it.
                                         * This means the location will be scanned precisely.
                                         * Tell the code at the beginning of the loop that this location is
                                         * processed.
                                         */
                                        if (reg_locations [i])
                                                DEBUG (fprintf (logfile, "\treg %s at location %p (==%p) is precise.\n", mono_arch_regname (i), reg_locations [i], (gpointer)*reg_locations [i]));
                                        reg_locations [i] = NULL;
                                }
                        }
                }

                tls->nframes ++;
        }

        /* Scan the remaining register save locations */
        for (i = 0; i < MONO_MAX_IREGS; ++i) {
                if (reg_locations [i]) {
                        DEBUG (fprintf (logfile, "\tscan saved reg location %p.\n", reg_locations [i]));
                        mono_gc_conservatively_scan_area (reg_locations [i], (char*)reg_locations [i] + SIZEOF_SLOT);
                        scanned_registers += SIZEOF_SLOT;
                }
                if (new_reg_locations [i]) {
                        DEBUG (fprintf (logfile, "\tscan saved reg location %p.\n", new_reg_locations [i]));
                        mono_gc_conservatively_scan_area (new_reg_locations [i], (char*)new_reg_locations [i] + SIZEOF_SLOT);
                        scanned_registers += SIZEOF_SLOT;
                }
        }

        if (stack_limit < stack_end) {
                DEBUG (fprintf (logfile, "\tscan remaining stack %p-%p (%d).\n", stack_limit, stack_end, (int)(stack_end - stack_limit)));
                mono_gc_conservatively_scan_area (stack_limit, stack_end);
                stats.scanned_native += stack_end - stack_limit;
        }

        DEBUG (fprintf (logfile, "Marked %d bytes, p=%d,c=%d out of %d.\n", scanned, scanned_precisely, scanned_conservatively, (int)(stack_end - stack_start)));

        stats.scanned_stacks += stack_end - stack_start;
        stats.scanned += scanned;
        stats.scanned_precisely += scanned_precisely;
        stats.scanned_conservatively += scanned_conservatively;
        stats.scanned_registers += scanned_registers;

        //mono_gc_conservatively_scan_area (stack_start, stack_end);
}

/*
 * precise_pass:
 *
 *   Mark a thread stack precisely based on information saved during the conservative
 * pass.
 */
static void
precise_pass (TlsData *tls, guint8 *stack_start, guint8 *stack_end)
{
        int findex, i;
        FrameInfo *fi;
        guint8 *frame_start;

        if (!tls)
                return;

        if (!tls->unwind_state.valid)
                return;

        for (findex = 0; findex < tls->nframes; findex ++) {
                /* Load information saved by the !precise pass */
                fi = &tls->frames [findex];
                frame_start = stack_start + fi->frame_start_offset;

                DEBUG (char *fname = mono_method_full_name (fi->ji->method, TRUE); fprintf (logfile, "Mark(1): %s\n", fname); g_free (fname));

                /* 
                 * FIXME: Add a function to mark using a bitmap, to avoid doing a 
                 * call for each object.
                 */

                /* Mark stack slots */
                if (fi->bitmap) {
                        guint8 *ref_bitmap = fi->bitmap;
                        gboolean live;

                        for (i = 0; i < fi->nslots; ++i) {
                                MonoObject **ptr = (MonoObject**)(frame_start + (i * SIZEOF_SLOT));

                                live = ref_bitmap [i / 8] & (1 << (i % 8));

                                if (live) {
                                        MonoObject *obj = *ptr;
                                        if (obj) {
                                                DEBUG (fprintf (logfile, "\tref %s0x%x(fp)=%p: %p ->", (guint8*)ptr >= (guint8*)fi->fp ? "" : "-", ABS ((int)((gssize)ptr - (gssize)fi->fp)), ptr, obj));
                                                *ptr = mono_gc_scan_object (obj);
                                                DEBUG (fprintf (logfile, " %p.\n", *ptr));
                                        } else {
                                                DEBUG (fprintf (logfile, "\tref %s0x%x(fp)=%p: %p.\n", (guint8*)ptr >= (guint8*)fi->fp ? "" : "-", ABS ((int)((gssize)ptr - (gssize)fi->fp)), ptr, obj));
                                        }
                                } else {
#if 0
                                        /*
                                         * This is disabled because the pointer takes up a lot of space.
                                         * Stack slots might be shared between ref and non-ref variables ?
                                         */
                                        if (map->ref_slots [i / 8] & (1 << (i % 8))) {
                                                DEBUG (fprintf (logfile, "\tref %s0x%x(fp)=%p: dead (%p)\n", (guint8*)ptr >= (guint8*)fi->fp ? "" : "-", ABS ((int)((gssize)ptr - (gssize)fi->fp)), ptr, *ptr));
                                                /*
                                                 * Fail fast if the live range is incorrect, and
                                                 * the JITted code tries to access this object
                                                 */
                                                *ptr = DEAD_REF;
                                        }
#endif
                                }
                        }
                }

                /* Mark registers */

                /*
                 * Registers are different from stack slots, they have no address where they
                 * are stored. Instead, some frame below this frame in the stack saves them
                 * in its prolog to the stack. We can mark this location precisely.
                 */
                for (i = 0; i < fi->nreg_locations; ++i) {
                        /*
                         * reg_locations [i] contains the address of the stack slot where
                         * a reg was last saved, so mark that slot.
                         */
                        MonoObject **ptr = (MonoObject**)((guint8*)stack_start + fi->reg_locations [i]);
                        MonoObject *obj = *ptr;

                        if (obj) {
                                DEBUG (fprintf (logfile, "\treg %s saved at %p: %p ->", mono_arch_regname (fi->regs [i]), ptr, obj));
                                *ptr = mono_gc_scan_object (obj);
                                DEBUG (fprintf (logfile, " %p.\n", *ptr));
                        } else {
                                DEBUG (fprintf (logfile, "\treg %s saved at %p: %p\n", mono_arch_regname (fi->regs [i]), ptr, obj));
                        }
                }       
        }

        /*
         * Debugging aid to check for missed refs.
         */
        if (tls->ref_to_track) {
                mgreg_t *p;

                for (p = (mgreg_t*)stack_start; p < (mgreg_t*)stack_end; ++p)
                        if (*p == (mgreg_t)tls->ref_to_track)
                                printf ("REF AT %p.\n", p);
        }
}

/*
 * thread_mark_func:
 *
 *   This is called by the GC twice to mark a thread stack. PRECISE is FALSE at the first
 * call, and TRUE at the second. USER_DATA points to a TlsData
 * structure filled up by thread_suspend_func. 
 */
static void
thread_mark_func (gpointer user_data, guint8 *stack_start, guint8 *stack_end, gboolean precise)
{
        TlsData *tls = user_data;

        DEBUG (fprintf (logfile, "****************************************\n"));
        DEBUG (fprintf (logfile, "*** %s stack marking for thread %p (%p-%p) ***\n", precise ? "Precise" : "Conservative", tls ? GUINT_TO_POINTER (tls->tid) : NULL, stack_start, stack_end));
        DEBUG (fprintf (logfile, "****************************************\n"));

        if (!precise)
                conservative_pass (tls, stack_start, stack_end);
        else
                precise_pass (tls, stack_start, stack_end);
}

static void
mini_gc_init_gc_map (MonoCompile *cfg)
{
        if (COMPILE_LLVM (cfg))
                return;

        if (!mono_gc_is_moving ())
                return;

        if (cfg->compile_aot) {
                if (!enable_gc_maps_for_aot)
                        return;
        } else if (!mono_gc_precise_stack_mark_enabled ())
                return;

#if 1
        /* Debugging support */
        {
                static int precise_count;

                precise_count ++;
                if (getenv ("MONO_GCMAP_COUNT")) {
                        if (precise_count == atoi (getenv ("MONO_GCMAP_COUNT")))
                                printf ("LAST: %s\n", mono_method_full_name (cfg->method, TRUE));
                        if (precise_count > atoi (getenv ("MONO_GCMAP_COUNT")))
                                return;
                }
        }
#endif

        cfg->compute_gc_maps = TRUE;

        cfg->gc_info = mono_mempool_alloc0 (cfg->mempool, sizeof (MonoCompileGC));
}

/*
 * mini_gc_set_slot_type_from_fp:
 *
 *   Set the GC slot type of the stack slot identified by SLOT_OFFSET, which should be
 * relative to the frame pointer. By default, all stack slots are type PIN, so there is no
 * need to call this function for those slots.
 */
void
mini_gc_set_slot_type_from_fp (MonoCompile *cfg, int slot_offset, GCSlotType type)
{
        MonoCompileGC *gcfg = (MonoCompileGC*)cfg->gc_info;

        if (!cfg->compute_gc_maps)
                return;

        g_assert (slot_offset % SIZEOF_SLOT == 0);

        gcfg->stack_slots_from_fp = g_slist_prepend_mempool (cfg->mempool, gcfg->stack_slots_from_fp, GINT_TO_POINTER (((slot_offset) << 16) | type));
}

/*
 * mini_gc_set_slot_type_from_cfa:
 *
 *   Set the GC slot type of the stack slot identified by SLOT_OFFSET, which should be
 * relative to the DWARF CFA value. This should be called from mono_arch_emit_prolog ().
 * If type is STACK_REF, the slot is assumed to be live from the end of the prolog until
 * the end of the method. By default, all stack slots are type PIN, so there is no need to
 * call this function for those slots.
 */
void
mini_gc_set_slot_type_from_cfa (MonoCompile *cfg, int slot_offset, GCSlotType type)
{
        MonoCompileGC *gcfg = (MonoCompileGC*)cfg->gc_info;
        int slot = - (slot_offset / SIZEOF_SLOT);

        if (!cfg->compute_gc_maps)
                return;

        g_assert (slot_offset <= 0);
        g_assert (slot_offset % SIZEOF_SLOT == 0);

        gcfg->stack_slots_from_cfa = g_slist_prepend_mempool (cfg->mempool, gcfg->stack_slots_from_cfa, GUINT_TO_POINTER (((slot) << 16) | type));
}

static inline int
fp_offset_to_slot (MonoCompile *cfg, int offset)
{
        MonoCompileGC *gcfg = cfg->gc_info;

        return (offset - gcfg->min_offset) / SIZEOF_SLOT;
}

static inline int
slot_to_fp_offset (MonoCompile *cfg, int slot)
{
        MonoCompileGC *gcfg = cfg->gc_info;

        return (slot * SIZEOF_SLOT) + gcfg->min_offset;
}

static inline void
set_slot (MonoCompileGC *gcfg, int slot, int callsite_index, GCSlotType type)
{
        g_assert (slot >= 0 && slot < gcfg->nslots);

        if (type == SLOT_PIN) {
                clear_bit (gcfg->stack_ref_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
                set_bit (gcfg->stack_pin_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
        } else if (type == SLOT_REF) {
                set_bit (gcfg->stack_ref_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
                clear_bit (gcfg->stack_pin_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
        } else if (type == SLOT_NOREF) {
                clear_bit (gcfg->stack_ref_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
                clear_bit (gcfg->stack_pin_bitmap, gcfg->stack_bitmap_width, callsite_index, slot);
        }
}

static inline void
set_slot_everywhere (MonoCompileGC *gcfg, int slot, GCSlotType type)
{
        int cindex;

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex)
                set_slot (gcfg, slot, cindex, type);
}

static inline void
set_slot_in_range (MonoCompileGC *gcfg, int slot, int from, int to, GCSlotType type)
{
        int cindex;

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex) {
                int callsite_offset = gcfg->callsites [cindex]->pc_offset;
                if (callsite_offset >= from && callsite_offset < to)
                        set_slot (gcfg, slot, cindex, type);
        }
}

static inline void
set_reg_slot (MonoCompileGC *gcfg, int slot, int callsite_index, GCSlotType type)
{
        g_assert (slot >= 0 && slot < gcfg->nregs);

        if (type == SLOT_PIN) {
                clear_bit (gcfg->reg_ref_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
                set_bit (gcfg->reg_pin_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
        } else if (type == SLOT_REF) {
                set_bit (gcfg->reg_ref_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
                clear_bit (gcfg->reg_pin_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
        } else if (type == SLOT_NOREF) {
                clear_bit (gcfg->reg_ref_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
                clear_bit (gcfg->reg_pin_bitmap, gcfg->reg_bitmap_width, callsite_index, slot);
        }
}

static inline void
set_reg_slot_everywhere (MonoCompileGC *gcfg, int slot, GCSlotType type)
{
        int cindex;

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex)
                set_reg_slot (gcfg, slot, cindex, type);
}

static inline void
set_reg_slot_in_range (MonoCompileGC *gcfg, int slot, int from, int to, GCSlotType type)
{
        int cindex;

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex) {
                int callsite_offset = gcfg->callsites [cindex]->pc_offset;
                if (callsite_offset >= from && callsite_offset < to)
                        set_reg_slot (gcfg, slot, cindex, type);
        }
}

static void
process_spill_slots (MonoCompile *cfg)
{
        MonoCompileGC *gcfg = cfg->gc_info;
        MonoBasicBlock *bb;
        GSList *l;
        int i;

        /* Mark all ref/pin spill slots as NOREF by default outside of their live range */
        for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
                for (l = bb->spill_slot_defs; l; l = l->next) {
                        MonoInst *def = l->data;
                        int spill_slot = def->inst_c0;
                        int bank = def->inst_c1;
                        int offset = cfg->spill_info [bank][spill_slot].offset;
                        int slot = fp_offset_to_slot (cfg, offset);

                        if (bank == MONO_REG_INT_MP || bank == MONO_REG_INT_REF)
                                set_slot_everywhere (gcfg, slot, SLOT_NOREF);
                }
        }

        for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
                for (l = bb->spill_slot_defs; l; l = l->next) {
                        MonoInst *def = l->data;
                        int spill_slot = def->inst_c0;
                        int bank = def->inst_c1;
                        int offset = cfg->spill_info [bank][spill_slot].offset;
                        int slot = fp_offset_to_slot (cfg, offset);
                        GCSlotType type;

                        if (bank == MONO_REG_INT_MP)
                                type = SLOT_PIN;
                        else
                                type = SLOT_REF;

                        /*
                         * Extend the live interval for the GC tracked spill slots
                         * defined in this bblock.
                         * FIXME: This is not needed.
                         */
                        set_slot_in_range (gcfg, slot, def->backend.pc_offset, bb->native_offset + bb->native_length, type);

                        if (cfg->verbose_level > 1)
                                printf ("\t%s spill slot at %s0x%x(fp) (slot = %d)\n", slot_type_to_string (type), offset >= 0 ? "" : "-", ABS (offset), slot);
                }
        }

        /* Set fp spill slots to NOREF */
        for (i = 0; i < cfg->spill_info_len [MONO_REG_DOUBLE]; ++i) {
                int offset = cfg->spill_info [MONO_REG_DOUBLE][i].offset;
                int slot;

                if (offset == -1)
                        continue;

                slot = fp_offset_to_slot (cfg, offset);

                set_slot_everywhere (gcfg, slot, SLOT_NOREF);
                /* FIXME: 32 bit */
                if (cfg->verbose_level > 1)
                        printf ("\tfp spill slot at %s0x%x(fp) (slot = %d)\n", offset >= 0 ? "" : "-", ABS (offset), slot);
        }

        /* Set int spill slots to NOREF */
        for (i = 0; i < cfg->spill_info_len [MONO_REG_INT]; ++i) {
                int offset = cfg->spill_info [MONO_REG_INT][i].offset;
                int slot;

                if (offset == -1)
                        continue;

                slot = fp_offset_to_slot (cfg, offset);

                set_slot_everywhere (gcfg, slot, SLOT_NOREF);
                if (cfg->verbose_level > 1)
                        printf ("\tint spill slot at %s0x%x(fp) (slot = %d)\n", offset >= 0 ? "" : "-", ABS (offset), slot);
        }
}

/*
 * process_other_slots:
 *
 *   Process stack slots registered using mini_gc_set_slot_type_... ().
 */
static void
process_other_slots (MonoCompile *cfg)
{
        MonoCompileGC *gcfg = cfg->gc_info;
        GSList *l;

        /* Relative to the CFA */
        for (l = gcfg->stack_slots_from_cfa; l; l = l->next) {
                guint data = GPOINTER_TO_UINT (l->data);
                int cfa_slot = data >> 16;
                GCSlotType type = data & 0xff;
                int slot;
                
                /*
                 * Map the cfa relative slot to an fp relative slot.
                 * slot_addr == cfa - <cfa_slot>*4/8
                 * fp + cfa_offset == cfa
                 * -> slot_addr == fp + (cfa_offset - <cfa_slot>*4/8)
                 */
                slot = (cfg->cfa_offset / SIZEOF_SLOT) - cfa_slot - (gcfg->min_offset / SIZEOF_SLOT);

                set_slot_everywhere (gcfg, slot, type);

                if (cfg->verbose_level > 1) {
                        int fp_offset = slot_to_fp_offset (cfg, slot);
                        if (type == SLOT_NOREF)
                                printf ("\tnoref slot at %s0x%x(fp) (slot = %d) (cfa - 0x%x)\n", fp_offset >= 0 ? "" : "-", ABS (fp_offset), slot, (int)(cfa_slot * SIZEOF_SLOT));
                }
        }

        /* Relative to the FP */
        for (l = gcfg->stack_slots_from_fp; l; l = l->next) {
                gint data = GPOINTER_TO_INT (l->data);
                int offset = data >> 16;
                GCSlotType type = data & 0xff;
                int slot;
                
                slot = fp_offset_to_slot (cfg, offset);

                set_slot_everywhere (gcfg, slot, type);

                /* Liveness for these slots is handled by process_spill_slots () */

                if (cfg->verbose_level > 1) {
                        if (type == SLOT_REF)
                                printf ("\tref slot at fp+0x%x (slot = %d)\n", offset, slot);
                        else if (type == SLOT_NOREF)
                                printf ("\tnoref slot at 0x%x(fp) (slot = %d)\n", offset, slot);
                }
        }
}

static gsize*
get_vtype_bitmap (MonoType *t, int *numbits)
{
        MonoClass *klass = mono_class_from_mono_type (t);

        if (klass->generic_container || mono_class_is_open_constructed_type (t)) {
                /* FIXME: Generic sharing */
                return NULL;
        } else {
                mono_class_compute_gc_descriptor (klass);

                return mono_gc_get_bitmap_for_descr (klass->gc_descr, numbits);
        }
}

static inline const char*
get_offset_sign (int offset)
{
        return offset < 0 ? "-" : "+";
}

static inline int
get_offset_val (int offset)
{
        return offset < 0 ? (- offset) : offset;
}

static void
process_variables (MonoCompile *cfg)
{
        MonoCompileGC *gcfg = cfg->gc_info;
        MonoMethodSignature *sig = mono_method_signature (cfg->method);
        int i, locals_min_slot, locals_max_slot, cindex;
        MonoBasicBlock *bb;
        MonoInst *tmp;
        int *pc_offsets;
        int locals_min_offset = gcfg->locals_min_offset;
        int locals_max_offset = gcfg->locals_max_offset;

        /* Slots for locals are NOREF by default */
        locals_min_slot = (locals_min_offset - gcfg->min_offset) / SIZEOF_SLOT;
        locals_max_slot = (locals_max_offset - gcfg->min_offset) / SIZEOF_SLOT;
        for (i = locals_min_slot; i < locals_max_slot; ++i) {
                set_slot_everywhere (gcfg, i, SLOT_NOREF);
        }

        /*
         * Compute the offset where variables are initialized in the first bblock, if any.
         */
        pc_offsets = g_new0 (int, cfg->next_vreg);

        bb = cfg->bb_entry->next_bb;
        MONO_BB_FOR_EACH_INS (bb, tmp) {
                if (tmp->opcode == OP_GC_LIVENESS_DEF) {
                        int vreg = tmp->inst_c1;
                        if (pc_offsets [vreg] == 0) {
                                g_assert (tmp->backend.pc_offset > 0);
                                pc_offsets [vreg] = tmp->backend.pc_offset;
                        }
                }
        }

        /*
         * Stack slots holding arguments are initialized in the prolog.
         * This means we can treat them alive for the whole method.
         */
        for (i = 0; i < cfg->num_varinfo; i++) {
                MonoInst *ins = cfg->varinfo [i];
                MonoType *t = ins->inst_vtype;
                MonoMethodVar *vmv;
                guint32 pos;
                gboolean byref, is_this = FALSE;
                gboolean is_arg = i < cfg->locals_start;

                if (ins == cfg->ret) {
                        if (!(ins->opcode == OP_REGOFFSET && MONO_TYPE_ISSTRUCT (t)))
                                continue;
                }

                vmv = MONO_VARINFO (cfg, i);

                /* For some reason, 'this' is byref */
                if (sig->hasthis && ins == cfg->args [0] && !cfg->method->klass->valuetype) {
                        t = &cfg->method->klass->byval_arg;
                        is_this = TRUE;
                }

                byref = t->byref;

                if (ins->opcode == OP_REGVAR) {
                        int hreg;
                        GCSlotType slot_type;

                        t = mini_type_get_underlying_type (NULL, t);

                        hreg = ins->dreg;
                        g_assert (hreg < MONO_MAX_IREGS);

                        if (byref)
                                slot_type = SLOT_PIN;
                        else
                                slot_type = mini_type_is_reference (cfg, t) ? SLOT_REF : SLOT_NOREF;

                        if (slot_type == SLOT_PIN) {
                                /* These have no live interval, be conservative */
                                set_reg_slot_everywhere (gcfg, hreg, slot_type);
                        } else {
                                /*
                                 * Unlike variables allocated to the stack, we generate liveness info
                                 * for noref vars in registers in mono_spill_global_vars (), because
                                 * knowing that a register doesn't contain a ref allows us to mark its save
                                 * locations precisely.
                                 */
                                for (cindex = 0; cindex < gcfg->ncallsites; ++cindex)
                                        if (gcfg->callsites [cindex]->liveness [i / 8] & (1 << (i % 8)))
                                                set_reg_slot (gcfg, hreg, cindex, slot_type);
                        }

                        if (cfg->verbose_level > 1) {
                                printf ("\t%s %sreg %s(R%d)\n", slot_type_to_string (slot_type), is_arg ? "arg " : "", mono_arch_regname (hreg), vmv->vreg);
                        }

                        continue;
                }

                if (ins->opcode != OP_REGOFFSET)
                        continue;

                if (ins->inst_offset % SIZEOF_SLOT != 0)
                        continue;

                if (is_arg && ins->inst_offset >= gcfg->max_offset)
                        /* In parent frame */
                        continue;

                pos = fp_offset_to_slot (cfg, ins->inst_offset);

                if (is_arg && ins->flags & MONO_INST_IS_DEAD) {
                        /* These do not get stored in the prolog */
                        set_slot_everywhere (gcfg, pos, SLOT_NOREF);

                        if (cfg->verbose_level > 1) {
                                printf ("\tdead arg at fp%s0x%x (slot = %d): %s\n", get_offset_sign (ins->inst_offset), get_offset_val (ins->inst_offset), pos, mono_type_full_name (ins->inst_vtype));
                        }
                        continue;
                }

                if (MONO_TYPE_ISSTRUCT (t)) {
                        int numbits = 0, j;
                        gsize *bitmap = NULL;
                        gboolean pin = FALSE;
                        int size;
                        int size_in_slots;
                        
                        if (ins->backend.is_pinvoke)
                                size = mono_class_native_size (ins->klass, NULL);
                        else
                                size = mono_class_value_size (ins->klass, NULL);
                        size_in_slots = ALIGN_TO (size, SIZEOF_SLOT) / SIZEOF_SLOT;

                        if (cfg->verbose_level > 1)
                                printf ("\tvtype R%d at %s0x%x(fp)-%s0x%x(fp) (slot %d-%d): %s\n", vmv->vreg, get_offset_sign (ins->inst_offset), get_offset_val (ins->inst_offset), get_offset_sign (ins->inst_offset), get_offset_val (ins->inst_offset + (size_in_slots * SIZEOF_SLOT)), pos, pos + size_in_slots, mono_type_full_name (ins->inst_vtype));

                        if (!ins->klass->has_references) {
                                if (is_arg) {
                                        for (j = 0; j < size_in_slots; ++j)
                                                set_slot_everywhere (gcfg, pos + j, SLOT_NOREF);
                                }
                                continue;
                        }

                        bitmap = get_vtype_bitmap (t, &numbits);
                        if (!bitmap)
                                pin = TRUE;

                        /*
                         * Most vtypes are marked volatile because of the LDADDR instructions,
                         * and they have no liveness information since they are decomposed
                         * before the liveness pass. We emit OP_GC_LIVENESS_DEF instructions for
                         * them during VZERO decomposition.
                         */
                        if (!pc_offsets [vmv->vreg])
                                pin = TRUE;

                        if (ins->backend.is_pinvoke)
                                pin = TRUE;

                        if (bitmap) {
                                for (cindex = 0; cindex < gcfg->ncallsites; ++cindex) {
                                        if (gcfg->callsites [cindex]->pc_offset > pc_offsets [vmv->vreg]) {
                                                for (j = 0; j < numbits; ++j) {
                                                        if (bitmap [j / GC_BITS_PER_WORD] & ((gsize)1 << (j % GC_BITS_PER_WORD))) {
                                                                /* The descriptor is for the boxed object */
                                                                set_slot (gcfg, (pos + j - (sizeof (MonoObject) / SIZEOF_SLOT)), cindex, pin ? SLOT_PIN : SLOT_REF);
                                                        }
                                                }
                                        }
                                }

                                if (cfg->verbose_level > 1) {
                                        for (j = 0; j < numbits; ++j) {
                                                if (bitmap [j / GC_BITS_PER_WORD] & ((gsize)1 << (j % GC_BITS_PER_WORD)))
                                                        printf ("\t\t%s slot at 0x%x(fp) (slot = %d)\n", pin ? "pin" : "ref", (int)(ins->inst_offset + (j * SIZEOF_SLOT)), (int)(pos + j - (sizeof (MonoObject) / SIZEOF_SLOT)));
                                        }
                                }
                        } else {
                                if (cfg->verbose_level > 1)
                                        printf ("\t\tpinned\n");
                                for (j = 0; j < size_in_slots; ++j) {
                                        set_slot_everywhere (gcfg, pos + j, SLOT_PIN);
                                }
                        }

                        g_free (bitmap);

                        continue;
                }

                if (!is_arg && (ins->inst_offset < gcfg->min_offset || ins->inst_offset >= gcfg->max_offset))
                        /* Vret addr etc. */
                        continue;

                if (t->byref) {
                        if (is_arg) {
                                set_slot_everywhere (gcfg, pos, SLOT_PIN);
                        } else {
                                for (cindex = 0; cindex < gcfg->ncallsites; ++cindex)
                                        if (gcfg->callsites [cindex]->liveness [i / 8] & (1 << (i % 8)))
                                                set_slot (gcfg, pos, cindex, SLOT_PIN);
                        }
                        if (cfg->verbose_level > 1)
                                printf ("\tbyref at %s0x%x(fp) (R%d, slot = %d): %s\n", ins->inst_offset < 0 ? "-" : "", (ins->inst_offset < 0) ? -(int)ins->inst_offset : (int)ins->inst_offset, vmv->vreg, pos, mono_type_full_name (ins->inst_vtype));
                        continue;
                }

                /*
                 * This is currently disabled, but could be enabled to debug crashes.
                 */
#if 0
                if (t->type == MONO_TYPE_I) {
                        /*
                         * Variables created in mono_handle_global_vregs have type I, but they
                         * could hold GC refs since the vregs they were created from might not been
                         * marked as holding a GC ref. So be conservative.
                         */
                        set_slot_everywhere (gcfg, pos, SLOT_PIN);
                        continue;
                }
#endif

                t = mini_type_get_underlying_type (NULL, t);

                if (!mini_type_is_reference (cfg, t)) {
                        set_slot_everywhere (gcfg, pos, SLOT_NOREF);
                        if (cfg->verbose_level > 1)
                                printf ("\tnoref at %s0x%x(fp) (R%d, slot = %d): %s\n", ins->inst_offset < 0 ? "-" : "", (ins->inst_offset < 0) ? -(int)ins->inst_offset : (int)ins->inst_offset, vmv->vreg, pos, mono_type_full_name (ins->inst_vtype));
                        if (!t->byref && sizeof (mgreg_t) == 4 && (t->type == MONO_TYPE_I8 || t->type == MONO_TYPE_U8 || t->type == MONO_TYPE_R8)) {
                                set_slot_everywhere (gcfg, pos + 1, SLOT_NOREF);
                                if (cfg->verbose_level > 1)
                                        printf ("\tnoref at %s0x%x(fp) (R%d, slot = %d): %s\n", ins->inst_offset < 0 ? "-" : "", (ins->inst_offset < 0) ? -(int)(ins->inst_offset + 4) : (int)ins->inst_offset + 4, vmv->vreg, pos + 1, mono_type_full_name (ins->inst_vtype));
                        }
                        continue;
                }

                /* 'this' is marked INDIRECT for gshared methods */
                if (ins->flags & (MONO_INST_VOLATILE | MONO_INST_INDIRECT) && !is_this) {
                        /*
                         * For volatile variables, treat them alive from the point they are
                         * initialized in the first bblock until the end of the method.
                         */
                        if (is_arg) {
                                set_slot_everywhere (gcfg, pos, SLOT_REF);
                        } else if (pc_offsets [vmv->vreg]) {
                                set_slot_in_range (gcfg, pos, 0, pc_offsets [vmv->vreg], SLOT_PIN);
                                set_slot_in_range (gcfg, pos, pc_offsets [vmv->vreg], cfg->code_size, SLOT_REF);
                        } else {
                                set_slot_everywhere (gcfg, pos, SLOT_PIN);
                        }
                        if (cfg->verbose_level > 1)
                                printf ("\tvolatile ref at %s0x%x(fp) (R%d, slot = %d): %s\n", ins->inst_offset < 0 ? "-" : "", (ins->inst_offset < 0) ? -(int)ins->inst_offset : (int)ins->inst_offset, vmv->vreg, pos, mono_type_full_name (ins->inst_vtype));
                        continue;
                }

                if (is_arg) {
                        /* Live for the whole method */
                        set_slot_everywhere (gcfg, pos, SLOT_REF);
                } else {
                        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex)
                                if (gcfg->callsites [cindex]->liveness [i / 8] & (1 << (i % 8)))
                                        set_slot (gcfg, pos, cindex, SLOT_REF);
                }

                if (cfg->verbose_level > 1) {
                        printf ("\tref at %s0x%x(fp) (R%d, slot = %d): %s\n", ins->inst_offset < 0 ? "-" : "", (ins->inst_offset < 0) ? -(int)ins->inst_offset : (int)ins->inst_offset, vmv->vreg, pos, mono_type_full_name (ins->inst_vtype));
                }
        }

        g_free (pc_offsets);
}

static int
sp_offset_to_fp_offset (MonoCompile *cfg, int sp_offset)
{
        /* 
         * Convert a sp relative offset to a slot index. This is
         * platform specific.
         */
#ifdef TARGET_AMD64
        /* fp = sp + offset */
        g_assert (cfg->frame_reg == AMD64_RBP);
        return (- cfg->arch.sp_fp_offset + sp_offset);
#elif defined(TARGET_X86)
        /* The offset is computed from the sp at the start of the call sequence */
        g_assert (cfg->frame_reg == X86_EBP);
        return (- cfg->arch.sp_fp_offset - sp_offset);  
#else
        NOT_IMPLEMENTED;
        return -1;
#endif
}

static GCSlotType
type_to_gc_slot_type (MonoCompile *cfg, MonoType *t)
{
        if (t->byref)
                return SLOT_PIN;
        t = mini_type_get_underlying_type (NULL, t);
        if (mini_type_is_reference (cfg, t))
                return SLOT_REF;
        else {
                if (MONO_TYPE_ISSTRUCT (t)) {
                        MonoClass *klass = mono_class_from_mono_type (t);
                        if (!klass->has_references) {
                                return SLOT_NOREF;
                        } else {
                                // FIXME:
                                return SLOT_PIN;
                        }
                }
                return SLOT_NOREF;
        }
}

static void
process_param_area_slots (MonoCompile *cfg)
{
        MonoCompileGC *gcfg = cfg->gc_info;
        int cindex, i;
        gboolean *is_param;

        /*
         * These slots are used for passing parameters during calls. They are sp relative, not
         * fp relative, so they are harder to handle.
         */
        if (cfg->flags & MONO_CFG_HAS_ALLOCA)
                /* The distance between fp and sp is not constant */
                return;

        is_param = mono_mempool_alloc0 (cfg->mempool, gcfg->nslots * sizeof (gboolean));

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex) {
                GCCallSite *callsite = gcfg->callsites [cindex];
                GSList *l;

                for (l = callsite->param_slots; l; l = l->next) {
                        MonoInst *def = l->data;
                        MonoType *t = def->inst_vtype;
                        int sp_offset = def->inst_offset;
                        int fp_offset = sp_offset_to_fp_offset (cfg, sp_offset);
                        int slot = fp_offset_to_slot (cfg, fp_offset);
                        guint32 align;
                        guint32 size;

                        if (MONO_TYPE_ISSTRUCT (t)) {
                                size = mini_type_stack_size_full (cfg->generic_sharing_context, t, &align, FALSE);
                        } else {
                                size = sizeof (mgreg_t);
                        }

                        for (i = 0; i < size / sizeof (mgreg_t); ++i) {
                                g_assert (slot + i >= 0 && slot + i < gcfg->nslots);
                                is_param [slot + i] = TRUE;
                        }
                }
        }

        /* All param area slots are noref by default */
        for (i = 0; i < gcfg->nslots; ++i) {
                if (is_param [i])
                        set_slot_everywhere (gcfg, i, SLOT_NOREF);
        }

        for (cindex = 0; cindex < gcfg->ncallsites; ++cindex) {
                GCCallSite *callsite = gcfg->callsites [cindex];
                GSList *l;

                for (l = callsite->param_slots; l; l = l->next) {
                        MonoInst *def = l->data;
                        MonoType *t = def->inst_vtype;
                        int sp_offset = def->inst_offset;
                        int fp_offset = sp_offset_to_fp_offset (cfg, sp_offset);
                        int slot = fp_offset_to_slot (cfg, fp_offset);
                        GCSlotType type = type_to_gc_slot_type (cfg, t);

                        if (MONO_TYPE_ISSTRUCT (t)) {
                                guint32 align;
                                guint32 size;
                                int size_in_slots;
                                gsize *bitmap;
                                int j, numbits;

                                size = mini_type_stack_size_full (cfg->generic_sharing_context, t, &align, FALSE);
                                size_in_slots = ALIGN_TO (size, SIZEOF_SLOT) / SIZEOF_SLOT;

                                bitmap = get_vtype_bitmap (t, &numbits);
                                if (type == SLOT_NOREF || !bitmap) {
                                        for (i = 0; i < size_in_slots; ++i) {
                                                set_slot_in_range (gcfg, slot + i, def->backend.pc_offset, callsite->pc_offset + 1, type);
                                        }
                                        if (cfg->verbose_level > 1)
                                                printf ("\t%s param area slots at %s0x%x(fp)=0x%x(sp) (slot = %d-%d) [0x%x-0x%x]\n", slot_type_to_string (type), get_offset_sign (fp_offset), get_offset_val (fp_offset), sp_offset, slot, slot + (size / (int)sizeof (mgreg_t)), def->backend.pc_offset, callsite->pc_offset + 1);
                                } else {
                                        for (j = 0; j < numbits; ++j) {
                                                if (bitmap [j / GC_BITS_PER_WORD] & ((gsize)1 << (j % GC_BITS_PER_WORD))) {
                                                        /* The descriptor is for the boxed object */
                                                        set_slot (gcfg, (slot + j - (sizeof (MonoObject) / SIZEOF_SLOT)), cindex, SLOT_REF);
                                                }
                                        }
                                        if (cfg->verbose_level > 1)
                                                printf ("\tvtype param area slots at %s0x%x(fp)=0x%x(sp) (slot = %d-%d) [0x%x-0x%x]\n", get_offset_sign (fp_offset), get_offset_val (fp_offset), sp_offset, slot, slot + (size / (int)sizeof (mgreg_t)), def->backend.pc_offset, callsite->pc_offset + 1);
                                }
                                g_free (bitmap);
                        } else {
                                /* The slot is live between the def instruction and the call */
                                set_slot_in_range (gcfg, slot, def->backend.pc_offset, callsite->pc_offset + 1, type);
                                if (cfg->verbose_level > 1)
                                        printf ("\t%s param area slot at %s0x%x(fp)=0x%x(sp) (slot = %d) [0x%x-0x%x]\n", slot_type_to_string (type), get_offset_sign (fp_offset), get_offset_val (fp_offset), sp_offset, slot, def->backend.pc_offset, callsite->pc_offset + 1);
                        }
                }
        }
}

static void
process_finally_clauses (MonoCompile *cfg)
{
        MonoCompileGC *gcfg = cfg->gc_info;
        GCCallSite **callsites;
        int ncallsites;
        gboolean has_finally;
        int i, j, nslots, nregs;

        ncallsites = gcfg->ncallsites;
        nslots = gcfg->nslots;
        nregs = gcfg->nregs;
        callsites = gcfg->callsites;

        /*
         * The calls to the finally clauses don't show up in the cfg. See
         * test_0_liveness_8 ().
         * Variables accessed inside the finally clause are already marked VOLATILE by
         * mono_liveness_handle_exception_clauses (). Variables not accessed inside the finally clause have
         * correct liveness outside the finally clause. So mark them PIN inside the finally clauses.
         */
        has_finally = FALSE;
        for (i = 0; i < cfg->header->num_clauses; ++i) {
                MonoExceptionClause *clause = &cfg->header->clauses [i];

                if (clause->flags == MONO_EXCEPTION_CLAUSE_FINALLY) {
                        has_finally = TRUE;
                }
        }
        if (has_finally) {
                if (cfg->verbose_level > 1)
                        printf ("\tMethod has finally clauses, pessimizing live ranges.\n");
                for (j = 0; j < ncallsites; ++j) {
                        MonoBasicBlock *bb = callsites [j]->bb;
                        MonoExceptionClause *clause;
                        gboolean is_in_finally = FALSE;

                        for (i = 0; i < cfg->header->num_clauses; ++i) {
                                clause = &cfg->header->clauses [i];
                           
                                if (MONO_OFFSET_IN_HANDLER (clause, bb->real_offset)) {
                                        if (clause->flags == MONO_EXCEPTION_CLAUSE_FINALLY) {
                                                is_in_finally = TRUE;
                                                break;
                                        }
                                }
                        }

                        if (is_in_finally) {
                                for (i = 0; i < nslots; ++i)
                                        set_slot (gcfg, i, j, SLOT_PIN);
                                for (i = 0; i < nregs; ++i)
                                        set_reg_slot (gcfg, i, j, SLOT_PIN);
                        }
                }
        }
}

static void
compute_frame_size (MonoCompile *cfg)
{
        int i, locals_min_offset, locals_max_offset, cfa_min_offset, cfa_max_offset;
        int min_offset, max_offset;
        MonoCompileGC *gcfg = cfg->gc_info;
        MonoMethodSignature *sig = mono_method_signature (cfg->method);
        GSList *l;

        /* Compute min/max offsets from the fp */

        /* Locals */
#if defined(TARGET_AMD64) || defined(TARGET_X86) || defined(TARGET_ARM) || defined(TARGET_S390X)
        locals_min_offset = ALIGN_TO (cfg->locals_min_stack_offset, SIZEOF_SLOT);
        locals_max_offset = cfg->locals_max_stack_offset;
#else
        /* min/max stack offset needs to be computed in mono_arch_allocate_vars () */
        NOT_IMPLEMENTED;
#endif

        locals_min_offset = ALIGN_TO (locals_min_offset, SIZEOF_SLOT);
        locals_max_offset = ALIGN_TO (locals_max_offset, SIZEOF_SLOT);

        min_offset = locals_min_offset;
        max_offset = locals_max_offset;

        /* Arguments */
        for (i = 0; i < sig->param_count + sig->hasthis; ++i) {
                MonoInst *ins = cfg->args [i];

                if (ins->opcode == OP_REGOFFSET)
                        min_offset = MIN (min_offset, ins->inst_offset);
        }

        /* Cfa slots */
        g_assert (cfg->frame_reg == cfg->cfa_reg);
        g_assert (cfg->cfa_offset > 0);
        cfa_min_offset = 0;
        cfa_max_offset = cfg->cfa_offset;

        min_offset = MIN (min_offset, cfa_min_offset);
        max_offset = MAX (max_offset, cfa_max_offset);

        /* Fp relative slots */
        for (l = gcfg->stack_slots_from_fp; l; l = l->next) {
                gint data = GPOINTER_TO_INT (l->data);
                int offset = data >> 16;

                min_offset = MIN (min_offset, offset);
        }

        /* Spill slots */
        if (!(cfg->flags & MONO_CFG_HAS_SPILLUP)) {
                int stack_offset = ALIGN_TO (cfg->stack_offset, SIZEOF_SLOT);
                min_offset = MIN (min_offset, (-stack_offset));
        }

        /* Param area slots */
#ifdef TARGET_AMD64
        min_offset = MIN (min_offset, -cfg->arch.sp_fp_offset);
#elif defined(TARGET_X86)
        min_offset = MIN (min_offset, - (cfg->arch.sp_fp_offset + cfg->arch.param_area_size));
#elif defined(TARGET_ARM)
        // FIXME:
#elif defined(TARGET_s390X)
        // FIXME:
#else
        NOT_IMPLEMENTED;
#endif

        gcfg->min_offset = min_offset;
        gcfg->max_offset = max_offset;
        gcfg->locals_min_offset = locals_min_offset;
        gcfg->locals_max_offset = locals_max_offset;
}

static void
init_gcfg (MonoCompile *cfg)
{
        int i, nregs, nslots;
        MonoCompileGC *gcfg = cfg->gc_info;
        GCCallSite **callsites;
        int ncallsites;
        MonoBasicBlock *bb;
        GSList *l;

        /*
         * Collect callsites
         */
        ncallsites = 0;
        for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
                ncallsites += g_slist_length (bb->gc_callsites);
        }
        callsites = mono_mempool_alloc0 (cfg->mempool, ncallsites * sizeof (GCCallSite*));
        i = 0;
        for (bb = cfg->bb_entry; bb; bb = bb->next_bb) {
                for (l = bb->gc_callsites; l; l = l->next)
                        callsites [i++] = l->data;
        }

        /* The callsites should already be ordered by pc offset */
        for (i = 1; i < ncallsites; ++i)
                g_assert (callsites [i - 1]->pc_offset < callsites [i]->pc_offset);

        /*
         * The stack frame looks like this:
         *
         * <fp + max_offset> == cfa ->  <end of previous frame>
         *                              <other stack slots>
         *                              <locals>
         *                              <other stack slots>
         * fp + min_offset          ->
         * ...
         * fp                       ->
         */

        if (cfg->verbose_level > 1)
                printf ("GC Map for %s: 0x%x-0x%x\n", mono_method_full_name (cfg->method, TRUE), gcfg->min_offset, gcfg->max_offset);

        nslots = (gcfg->max_offset - gcfg->min_offset) / SIZEOF_SLOT;
        nregs = NREGS;

        gcfg->nslots = nslots;
        gcfg->nregs = nregs;
        gcfg->callsites = callsites;
        gcfg->ncallsites = ncallsites;
        gcfg->stack_bitmap_width = ALIGN_TO (nslots, 8) / 8;
        gcfg->reg_bitmap_width = ALIGN_TO (nregs, 8) / 8;
        gcfg->stack_ref_bitmap = mono_mempool_alloc0 (cfg->mempool, gcfg->stack_bitmap_width * ncallsites);
        gcfg->stack_pin_bitmap = mono_mempool_alloc0 (cfg->mempool, gcfg->stack_bitmap_width * ncallsites);
        gcfg->reg_ref_bitmap = mono_mempool_alloc0 (cfg->mempool, gcfg->reg_bitmap_width * ncallsites);
        gcfg->reg_pin_bitmap = mono_mempool_alloc0 (cfg->mempool, gcfg->reg_bitmap_width * ncallsites);

        /* All slots start out as PIN */
        memset (gcfg->stack_pin_bitmap, 0xff, gcfg->stack_bitmap_width * ncallsites);
        for (i = 0; i < nregs; ++i) {
                /*
                 * By default, registers are NOREF.
                 * It is possible for a callee to save them before being defined in this method,
                 * but the saved value is dead too, so it doesn't need to be marked.
                 */
                if ((cfg->used_int_regs & (1 << i)))
                        set_reg_slot_everywhere (gcfg, i, SLOT_NOREF);
        }
}

static void
create_map (MonoCompile *cfg)
{
        GCMap *map;
        int i, j, nregs, nslots, nref_regs, npin_regs, alloc_size, bitmaps_size, bitmaps_offset;
        int ntypes [16];
        int stack_bitmap_width, stack_bitmap_size, reg_ref_bitmap_width, reg_ref_bitmap_size;
        int reg_pin_bitmap_width, reg_pin_bitmap_size, bindex;
        int start, end;
        gboolean has_ref_slots, has_pin_slots, has_ref_regs, has_pin_regs;
        MonoCompileGC *gcfg = cfg->gc_info;
        GCCallSite **callsites;
        int ncallsites;
        guint8 *bitmap, *bitmaps;
        guint32 reg_ref_mask, reg_pin_mask;

        ncallsites = gcfg->ncallsites;
        nslots = gcfg->nslots;
        nregs = gcfg->nregs;
        callsites = gcfg->callsites;

        /* 
         * Compute the real size of the bitmap i.e. ignore NOREF columns at the beginning and at
         * the end. Also, compute whenever the map needs ref/pin bitmaps, and collect stats.
         */
        has_ref_slots = FALSE;
        has_pin_slots = FALSE;
        start = -1;
        end = -1;
        memset (ntypes, 0, sizeof (ntypes));
        for (i = 0; i < nslots; ++i) {
                gboolean has_ref = FALSE;
                gboolean has_pin = FALSE;

                for (j = 0; j < ncallsites; ++j) {
                        if (get_bit (gcfg->stack_pin_bitmap, gcfg->stack_bitmap_width, j, i))
                                has_pin = TRUE;
                        if (get_bit (gcfg->stack_ref_bitmap, gcfg->stack_bitmap_width, j, i))
                                has_ref = TRUE;
                }

                if (has_ref)
                        has_ref_slots = TRUE;
                if (has_pin)
                        has_pin_slots = TRUE;

                if (has_ref)
                        ntypes [SLOT_REF] ++;
                else if (has_pin)
                        ntypes [SLOT_PIN] ++;
                else
                        ntypes [SLOT_NOREF] ++;

                if (has_ref || has_pin) {
                        if (start == -1)
                                start = i;
                        end = i + 1;
                }
        }
        if (start == -1) {
                start = end = nslots;
        } else {
                g_assert (start != -1);
                g_assert (start < end);
        }

        has_ref_regs = FALSE;
        has_pin_regs = FALSE;
        reg_ref_mask = 0;
        reg_pin_mask = 0;
        nref_regs = 0;
        npin_regs = 0;
        for (i = 0; i < nregs; ++i) {
                gboolean has_ref = FALSE;
                gboolean has_pin = FALSE;

                if (!(cfg->used_int_regs & (1 << i)))
                        continue;

                for (j = 0; j < ncallsites; ++j) {
                        if (get_bit (gcfg->reg_ref_bitmap, gcfg->reg_bitmap_width, j, i)) {
                                has_ref = TRUE;
                                break;
                        }
                }
                for (j = 0; j < ncallsites; ++j) {
                        if (get_bit (gcfg->reg_pin_bitmap, gcfg->reg_bitmap_width, j, i)) {
                                has_pin = TRUE;
                                break;
                        }
                }

                if (has_ref) {
                        reg_ref_mask |= (1 << i);
                        has_ref_regs = TRUE;
                        nref_regs ++;
                }
                if (has_pin) {
                        reg_pin_mask |= (1 << i);
                        has_pin_regs = TRUE;
                        npin_regs ++;
                }
        }

        if (cfg->verbose_level > 1)
                printf ("Slots: %d Start: %d End: %d Refs: %d NoRefs: %d Pin: %d Callsites: %d\n", nslots, start, end, ntypes [SLOT_REF], ntypes [SLOT_NOREF], ntypes [SLOT_PIN], ncallsites);

        /* Create the GC Map */

        stack_bitmap_width = ALIGN_TO (end - start, 8) / 8;
        stack_bitmap_size = stack_bitmap_width * ncallsites;
        reg_ref_bitmap_width = ALIGN_TO (nref_regs, 8) / 8;
        reg_ref_bitmap_size = reg_ref_bitmap_width * ncallsites;
        reg_pin_bitmap_width = ALIGN_TO (npin_regs, 8) / 8;
        reg_pin_bitmap_size = reg_pin_bitmap_width * ncallsites;
        bitmaps_size = (has_ref_slots ? stack_bitmap_size : 0) + (has_pin_slots ? stack_bitmap_size : 0) + (has_ref_regs ? reg_ref_bitmap_size : 0) + (has_pin_regs ? reg_pin_bitmap_size : 0);
        
        map = mono_mempool_alloc0 (cfg->mempool, sizeof (GCMap));

        map->frame_reg = cfg->frame_reg;
        map->start_offset = gcfg->min_offset;
        map->end_offset = gcfg->min_offset + (nslots * SIZEOF_SLOT);
        map->map_offset = start * SIZEOF_SLOT;
        map->nslots = end - start;
        map->has_ref_slots = has_ref_slots;
        map->has_pin_slots = has_pin_slots;
        map->has_ref_regs = has_ref_regs;
        map->has_pin_regs = has_pin_regs;
        g_assert (nregs < 32);
        map->used_int_regs = cfg->used_int_regs;
        map->reg_ref_mask = reg_ref_mask;
        map->reg_pin_mask = reg_pin_mask;
        map->nref_regs = nref_regs;
        map->npin_regs = npin_regs;

        bitmaps = mono_mempool_alloc0 (cfg->mempool, bitmaps_size);

        bitmaps_offset = 0;
        if (has_ref_slots) {
                map->stack_ref_bitmap_offset = bitmaps_offset;
                bitmaps_offset += stack_bitmap_size;

                bitmap = &bitmaps [map->stack_ref_bitmap_offset];
                for (i = 0; i < nslots; ++i) {
                        for (j = 0; j < ncallsites; ++j) {
                                if (get_bit (gcfg->stack_ref_bitmap, gcfg->stack_bitmap_width, j, i))
                                        set_bit (bitmap, stack_bitmap_width, j, i - start);
                        }
                }
        }
        if (has_pin_slots) {
                map->stack_pin_bitmap_offset = bitmaps_offset;
                bitmaps_offset += stack_bitmap_size;

                bitmap = &bitmaps [map->stack_pin_bitmap_offset];
                for (i = 0; i < nslots; ++i) {
                        for (j = 0; j < ncallsites; ++j) {
                                if (get_bit (gcfg->stack_pin_bitmap, gcfg->stack_bitmap_width, j, i))
                                        set_bit (bitmap, stack_bitmap_width, j, i - start);
                        }
                }
        }
        if (has_ref_regs) {
                map->reg_ref_bitmap_offset = bitmaps_offset;
                bitmaps_offset += reg_ref_bitmap_size;

                bitmap = &bitmaps [map->reg_ref_bitmap_offset];
                bindex = 0;
                for (i = 0; i < nregs; ++i) {
                        if (reg_ref_mask & (1 << i)) {
                                for (j = 0; j < ncallsites; ++j) {
                                        if (get_bit (gcfg->reg_ref_bitmap, gcfg->reg_bitmap_width, j, i))
                                                set_bit (bitmap, reg_ref_bitmap_width, j, bindex);
                                }
                                bindex ++;
                        }
                }
        }
        if (has_pin_regs) {
                map->reg_pin_bitmap_offset = bitmaps_offset;
                bitmaps_offset += reg_pin_bitmap_size;

                bitmap = &bitmaps [map->reg_pin_bitmap_offset];
                bindex = 0;
                for (i = 0; i < nregs; ++i) {
                        if (reg_pin_mask & (1 << i)) {
                                for (j = 0; j < ncallsites; ++j) {
                                        if (get_bit (gcfg->reg_pin_bitmap, gcfg->reg_bitmap_width, j, i))
                                                set_bit (bitmap, reg_pin_bitmap_width, j, bindex);
                                }
                                bindex ++;
                        }
                }
        }

        /* Call sites */
        map->ncallsites = ncallsites;
        if (cfg->code_len < 256)
                map->callsite_entry_size = 1;
        else if (cfg->code_len < 65536)
                map->callsite_entry_size = 2;
        else
                map->callsite_entry_size = 4;

        /* Encode the GC Map */
        {
                guint8 buf [256];
                guint8 *endbuf;
                GCEncodedMap *emap;
                int encoded_size;
                guint8 *p;

                encode_gc_map (map, buf, &endbuf);
                g_assert (endbuf - buf < 256);

                encoded_size = endbuf - buf;
                alloc_size = sizeof (GCEncodedMap) + ALIGN_TO (encoded_size, map->callsite_entry_size) + (map->callsite_entry_size * map->ncallsites) + bitmaps_size;

                emap = mono_domain_alloc0 (cfg->domain, alloc_size);
                //emap->ref_slots = map->ref_slots;

                /* Encoded fixed fields */
                p = &emap->encoded [0];
                //emap->encoded_size = encoded_size;
                memcpy (p, buf, encoded_size);
                p += encoded_size;

                /* Callsite table */
                p = (guint8*)ALIGN_TO ((mgreg_t)p, map->callsite_entry_size);
                if (map->callsite_entry_size == 1) {
                        guint8 *offsets = p;
                        for (i = 0; i < ncallsites; ++i)
                                offsets [i] = callsites [i]->pc_offset;
                        stats.gc_callsites8_size += ncallsites * sizeof (guint8);
                } else if (map->callsite_entry_size == 2) {
                        guint16 *offsets = (guint16*)p;
                        for (i = 0; i < ncallsites; ++i)
                                offsets [i] = callsites [i]->pc_offset;
                        stats.gc_callsites16_size += ncallsites * sizeof (guint16);
                } else {
                        guint32 *offsets = (guint32*)p;
                        for (i = 0; i < ncallsites; ++i)
                                offsets [i] = callsites [i]->pc_offset;
                        stats.gc_callsites32_size += ncallsites * sizeof (guint32);
                }
                p += ncallsites * map->callsite_entry_size;

                /* Bitmaps */
                memcpy (p, bitmaps, bitmaps_size);
                p += bitmaps_size;

                g_assert ((guint8*)p - (guint8*)emap <= alloc_size);

                stats.gc_maps_size += alloc_size;
                stats.gc_callsites_size += ncallsites * map->callsite_entry_size;
                stats.gc_bitmaps_size += bitmaps_size;
                stats.gc_map_struct_size += sizeof (GCEncodedMap) + encoded_size;

                cfg->jit_info->gc_info = emap;

                cfg->gc_map = (guint8*)emap;
                cfg->gc_map_size = alloc_size;
        }

        stats.all_slots += nslots;
        stats.ref_slots += ntypes [SLOT_REF];
        stats.noref_slots += ntypes [SLOT_NOREF];
        stats.pin_slots += ntypes [SLOT_PIN];
}

void
mini_gc_create_gc_map (MonoCompile *cfg)
{
        if (!cfg->compute_gc_maps)
                return;

        /*
         * During marking, all frames except the top frame are at a call site, and we mark the
         * top frame conservatively. This means that we only need to compute and record
         * GC maps for call sites.
         */

        if (!(cfg->comp_done & MONO_COMP_LIVENESS))
                /* Without liveness info, the live ranges are not precise enough */
                return;

        mono_analyze_liveness_gc (cfg);

        compute_frame_size (cfg);

        init_gcfg (cfg);

        process_spill_slots (cfg);
        process_other_slots (cfg);
        process_param_area_slots (cfg);
        process_variables (cfg);
        process_finally_clauses (cfg);

        create_map (cfg);
}

static void
parse_debug_options (void)
{
        char **opts, **ptr;
        char *env;

        env = getenv ("MONO_GCMAP_DEBUG");
        if (!env)
                return;

        opts = g_strsplit (env, ",", -1);
        for (ptr = opts; ptr && *ptr; ptr ++) {
                /* No options yet */
                fprintf (stderr, "Invalid format for the MONO_GCMAP_DEBUG env variable: '%s'\n", env);
                exit (1);
        }
        g_strfreev (opts);
}

void
mini_gc_init (void)
{
        MonoGCCallbacks cb;

        memset (&cb, 0, sizeof (cb));
        cb.thread_attach_func = thread_attach_func;
        cb.thread_detach_func = thread_detach_func;
        cb.thread_suspend_func = thread_suspend_func;
        /* Comment this out to disable precise stack marking */
        cb.thread_mark_func = thread_mark_func;
        mono_gc_set_gc_callbacks (&cb);

        logfile = mono_gc_get_logfile ();

        parse_debug_options ();

        mono_counters_register ("GC Maps size",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_maps_size);
        mono_counters_register ("GC Call Sites size",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_callsites_size);
        mono_counters_register ("GC Bitmaps size",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_bitmaps_size);
        mono_counters_register ("GC Map struct size",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_map_struct_size);
        mono_counters_register ("GC Call Sites encoded using 8 bits",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_callsites8_size);
        mono_counters_register ("GC Call Sites encoded using 16 bits",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_callsites16_size);
        mono_counters_register ("GC Call Sites encoded using 32 bits",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.gc_callsites32_size);

        mono_counters_register ("GC Map slots (all)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.all_slots);
        mono_counters_register ("GC Map slots (ref)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.ref_slots);
        mono_counters_register ("GC Map slots (noref)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.noref_slots);
        mono_counters_register ("GC Map slots (pin)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.pin_slots);

        mono_counters_register ("GC TLS Data size",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.tlsdata_size);

        mono_counters_register ("Stack space scanned (all)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_stacks);
        mono_counters_register ("Stack space scanned (native)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_native);
        mono_counters_register ("Stack space scanned (other)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_other);
        mono_counters_register ("Stack space scanned (using GC Maps)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned);
        mono_counters_register ("Stack space scanned (precise)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_precisely);
        mono_counters_register ("Stack space scanned (pin)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_conservatively);
        mono_counters_register ("Stack space scanned (pin registers)",
                                                        MONO_COUNTER_GC | MONO_COUNTER_INT, &stats.scanned_registers);
}

#else

void
mini_gc_init (void)
{
}

static void
mini_gc_init_gc_map (MonoCompile *cfg)
{
}

void
mini_gc_create_gc_map (MonoCompile *cfg)
{
}

void
mini_gc_set_slot_type_from_fp (MonoCompile *cfg, int slot_offset, GCSlotType type)
{
}

void
mini_gc_set_slot_type_from_cfa (MonoCompile *cfg, int slot_offset, GCSlotType type)
{
}

#endif

/*
 * mini_gc_init_cfg:
 *
 *   Set GC specific options in CFG.
 */
void
mini_gc_init_cfg (MonoCompile *cfg)
{
        if (mono_gc_is_moving ()) {
                cfg->disable_ref_noref_stack_slot_share = TRUE;
                cfg->gen_write_barriers = TRUE;
        }

        mini_gc_init_gc_map (cfg);
}

/*
 * Problems with the current code:
 * - the stack walk is slow
 * - vtypes/refs used in EH regions are treated conservatively
 * - if the code is finished, less pinning will be done, causing problems because
 *   we promote all surviving objects to old-gen.
 * - the unwind code can't handle a method stopped inside a finally region, it thinks the caller is
 *   another method, but in reality it is either the exception handling code or the CALL_HANDLER opcode.
 *   This manifests in "Unable to find ip offset x in callsite list" assertions.
 * - the unwind code also can't handle frames which are in the epilog, since the unwind info is not
 *   precise there.
 */

/*
 * Ideas for creating smaller GC maps:
 * - remove empty columns from the bitmaps. This requires adding a mask bit array for
 *   each bitmap.
 * - merge reg and stack slot bitmaps, so the unused bits at the end of the reg bitmap are
 *   not wasted.
 * - if the bitmap width is not a multiple of 8, the remaining bits are wasted.
 * - group ref and non-ref stack slots together in mono_allocate_stack_slots ().
 * - add an index for the callsite table so that each entry can be encoded as a 1 byte difference
 *   from an index entry.
 */