src/lj_target.h

   1 /*
   2 ** Definitions for target CPU.
   3 ** Copyright (C) 2005-2011 Mike Pall. See Copyright Notice in luajit.h
   4 */
   5
   6 #ifndef _LJ_TARGET_H
   7 #define _LJ_TARGET_H
   8
   9 #include "lj_def.h"
  10 #include "lj_arch.h"
  11
  12 /* -- Registers and spill slots ------------------------------------------- */
  13
  14 /* Register type (uint8_t in ir->r). */
  15 typedef uint32_t Reg;
  16
  17 /* The hi-bit is NOT set for an allocated register. This means the value
  18 ** can be directly used without masking. The hi-bit is set for a register
  19 ** allocation hint or for RID_INIT.
  20 */
  21 #define RID_NONE                0x80
  22 #define RID_MASK                0x7f
  23 #define RID_INIT                (RID_NONE|RID_MASK)
  24
  25 #define ra_noreg(r)             ((r) & RID_NONE)
  26 #define ra_hasreg(r)            (!((r) & RID_NONE))
  27
  28 /* The ra_hashint() macro assumes a previous test for ra_noreg(). */
  29 #define ra_hashint(r)           ((r) != RID_INIT)
  30 #define ra_gethint(r)           ((Reg)((r) & RID_MASK))
  31 #define ra_sethint(rr, r)       rr = (uint8_t)((r)|RID_NONE)
  32 #define ra_samehint(r1, r2)     (ra_gethint((r1)^(r2)) == 0)
  33
  34 /* Spill slot 0 means no spill slot has been allocated. */
  35 #define SPS_NONE                0
  36
  37 #define ra_hasspill(s)          ((s) != SPS_NONE)
  38
  39 /* Combined register and spill slot (uint16_t in ir->prev). */
  40 typedef uint32_t RegSP;
  41
  42 #define REGSP(r, s)             ((r) + ((s) << 8))
  43 #define REGSP_HINT(r)           ((r)|RID_NONE)
  44 #define REGSP_INIT              REGSP(RID_INIT, 0)
  45
  46 #define regsp_reg(rs)           ((rs) & 255)
  47 #define regsp_spill(rs)         ((rs) >> 8)
  48 #define regsp_used(rs) \
  49   (((rs) & ~REGSP(RID_MASK, 0)) != REGSP(RID_NONE, 0))
  50
  51 /* -- Register sets ------------------------------------------------------- */
  52
  53 /* Bitset for registers. 32 registers suffice for most architectures.
  54 ** Note that one set holds bits for both GPRs and FPRs.
  55 */
  56 #if LJ_TARGET_PPC
  57 typedef uint64_t RegSet;
  58 #else
  59 typedef uint32_t RegSet;
  60 #endif
  61
  62 #define RID2RSET(r)             (((RegSet)1) << (r))
  63 #define RSET_EMPTY              ((RegSet)0)
  64 #define RSET_RANGE(lo, hi)      ((RID2RSET((hi)-(lo))-1) << (lo))
  65
  66 #define rset_test(rs, r)        (((rs) >> (r)) & 1)
  67 #define rset_set(rs, r)         (rs |= RID2RSET(r))
  68 #define rset_clear(rs, r)       (rs &= ~RID2RSET(r))
  69 #define rset_exclude(rs, r)     (rs & ~RID2RSET(r))
  70 #if LJ_TARGET_PPC
  71 #define rset_picktop(rs)        ((Reg)(__builtin_clzll(rs)^63))
  72 #define rset_pickbot(rs)        ((Reg)__builtin_ctzll(rs))
  73 #else
  74 #define rset_picktop(rs)        ((Reg)lj_fls(rs))
  75 #define rset_pickbot(rs)        ((Reg)lj_ffs(rs))
  76 #endif
  77
  78 /* -- Register allocation cost -------------------------------------------- */
  79
  80 /* The register allocation heuristic keeps track of the cost for allocating
  81 ** a specific register:
  82 **
  83 ** A free register (obviously) has a cost of 0 and a 1-bit in the free mask.
  84 **
  85 ** An already allocated register has the (non-zero) IR reference in the lowest
  86 ** bits and the result of a blended cost-model in the higher bits.
  87 **
  88 ** The allocator first checks the free mask for a hit. Otherwise an (unrolled)
  89 ** linear search for the minimum cost is used. The search doesn't need to
  90 ** keep track of the position of the minimum, which makes it very fast.
  91 ** The lowest bits of the minimum cost show the desired IR reference whose
  92 ** register is the one to evict.
  93 **
  94 ** Without the cost-model this degenerates to the standard heuristics for
  95 ** (reverse) linear-scan register allocation. Since code generation is done
  96 ** in reverse, a live interval extends from the last use to the first def.
  97 ** For an SSA IR the IR reference is the first (and only) def and thus
  98 ** trivially marks the end of the interval. The LSRA heuristics says to pick
  99 ** the register whose live interval has the furthest extent, i.e. the lowest
 100 ** IR reference in our case.
 101 **
 102 ** A cost-model should take into account other factors, like spill-cost and
 103 ** restore- or rematerialization-cost, which depend on the kind of instruction.
 104 ** E.g. constants have zero spill costs, variant instructions have higher
 105 ** costs than invariants and PHIs should preferably never be spilled.
 106 **
 107 ** Here's a first cut at simple, but effective blended cost-model for R-LSRA:
 108 ** - Due to careful design of the IR, constants already have lower IR
 109 **   references than invariants and invariants have lower IR references
 110 **   than variants.
 111 ** - The cost in the upper 16 bits is the sum of the IR reference and a
 112 **   weighted score. The score currently only takes into account whether
 113 **   the IRT_ISPHI bit is set in the instruction type.
 114 ** - The PHI weight is the minimum distance (in IR instructions) a PHI
 115 **   reference has to be further apart from a non-PHI reference to be spilled.
 116 ** - It should be a power of two (for speed) and must be between 2 and 32768.
 117 **   Good values for the PHI weight seem to be between 40 and 150.
 118 ** - Further study is required.
 119 */
 120 #define REGCOST_PHI_WEIGHT      64
 121
 122 /* Cost for allocating a specific register. */
 123 typedef uint32_t RegCost;
 124
 125 /* Note: assumes 16 bit IRRef1. */
 126 #define REGCOST(cost, ref)      ((RegCost)(ref) + ((RegCost)(cost) << 16))
 127 #define regcost_ref(rc)         ((IRRef1)(rc))
 128
 129 #define REGCOST_T(t) \
 130   ((RegCost)((t)&IRT_ISPHI) * (((RegCost)(REGCOST_PHI_WEIGHT)<<16)/IRT_ISPHI))
 131 #define REGCOST_REF_T(ref, t)   (REGCOST((ref), (ref)) + REGCOST_T((t)))
 132
 133 /* -- Target-specific definitions ----------------------------------------- */
 134
 135 #if LJ_TARGET_X86ORX64
 136 #include "lj_target_x86.h"
 137 #elif LJ_TARGET_ARM
 138 #include "lj_target_arm.h"
 139 #elif LJ_TARGET_PPC
 140 #include "lj_target_ppc.h"
 141 #else
 142 #error "Missing include for target CPU"
 143 #endif
 144
 145 #ifdef EXITSTUBS_PER_GROUP
 146 /* Return the address of an exit stub. */
 147 static LJ_AINLINE char *exitstub_addr_(char **group, uint32_t exitno)
 148 {
 149   lua_assert(group[exitno / EXITSTUBS_PER_GROUP] != NULL);
 150   return (char *)group[exitno / EXITSTUBS_PER_GROUP] +
 151          EXITSTUB_SPACING*(exitno % EXITSTUBS_PER_GROUP);
 152 }
 153 /* Avoid dependence on lj_jit.h if only including lj_target.h. */
 154 #define exitstub_addr(J, exitno) \
 155   ((MCode *)exitstub_addr_((char **)((J)->exitstubgroup), (exitno)))
 156 #endif
 157
 158 #endif