rosenberg: handle bit fields better

[smatch.git] / simplify.c

/*
 * Simplify - do instruction simplification before CSE
 *
 * Copyright (C) 2004 Linus Torvalds
 */

///
// Instruction simplification
// --------------------------
//
// Notation
// ^^^^^^^^
// The following conventions are used to describe the simplications:
// * Uppercase letters are reserved for constants:
//   * `M` for a constant mask,
//   * `S` for a constant shift,
//   * `N` for a constant number of bits (usually other than a shift),
//   * `C` or 'K' for others constants.
// * Lowercase letters `a`, `b`, `x`, `y`, ... are used for non-constants
//   or when it doesn't matter if the pseudo is a constant or not.
// * Primes are used if needed to distinguish symbols (`M`, `M'`, ...).
// * Expressions or sub-expressions involving only constants are
//   understood to be evaluated.
// * `$mask(N)` is used for `((1 << N) -1)`
// * `$trunc(x, N)` is used for `(x & $mask(N))`
// * Expressions like `(-1 << S)`, `(-1 >> S)` and others formulae are
//   understood to be truncated to the size of the current instruction
//   (needed, since in general this size is not the same as the one used
//   by sparse for the evaluation of arithmetic operations).
// * `TRUNC(x, N)` is used for a truncation *to* a size of `N` bits
// * `ZEXT(x, N)` is used for a zero-extension *from* a size of `N` bits
// * `OP(x, C)` is used to represent some generic operation using a constant,
//   including when the constant is implicit (e.g. `TRUNC(x, N)`).
// * `MASK(x, M)` is used to respresent a 'masking' instruction:
//   - `AND(x, M)`
//   - `LSR(x, S)`, with `M` = (-1 << S)
//   - `SHL(x, S)`, with `M` = (-1 >> S)
//   - `TRUNC(x, N)`, with `M` = $mask(N)
//   - `ZEXT(x, N)`, with `M` = $mask(N)
// * `SHIFT(x, S)` is used for `LSR(x, S)` or `SHL(x, S)`.

#include <assert.h>

#include "parse.h"
#include "expression.h"
#include "linearize.h"
#include "simplify.h"
#include "flow.h"
#include "symbol.h"
#include "flowgraph.h"

///
// Utilities
// ^^^^^^^^^

///
// check if a pseudo is a power of 2
static inline bool is_pow2(pseudo_t src)
{
        if (src->type != PSEUDO_VAL)
                return false;
        return is_power_of_2(src->value);
}

///
// find the trivial parent for a phi-source
static struct basic_block *phi_parent(struct basic_block *source, pseudo_t pseudo)
{
        /* Can't go upwards if the pseudo is defined in the bb it came from.. */
        if (pseudo->type == PSEUDO_REG) {
                struct instruction *def = pseudo->def;
                if (def->bb == source)
                        return source;
        }
        if (bb_list_size(source->children) != 1 || bb_list_size(source->parents) != 1)
                return source;
        return first_basic_block(source->parents);
}

///
// copy the phi-node's phisrcs into to given array
// @return: 0 if the the list contained the expected
//      number of element, a positive number if there was
//      more than expected and a negative one if less.
//
// :note: we can't reuse a function like linearize_ptr_list()
//      because any VOIDs in the phi-list must be ignored here
//      as in this context they mean 'entry has been removed'.
static int get_phisources(struct instruction *sources[], int nbr, struct instruction *insn)
{
        pseudo_t phi;
        int i = 0;

        assert(insn->opcode == OP_PHI);
        FOR_EACH_PTR(insn->phi_list, phi) {
                struct instruction *def;
                if (phi == VOID)
                        continue;
                if (i >= nbr)
                        return 1;
                def = phi->def;
                assert(def->opcode == OP_PHISOURCE);
                sources[i++] = def;
        } END_FOR_EACH_PTR(phi);
        return i - nbr;
}

static int if_convert_phi(struct instruction *insn)
{
        struct instruction *array[2];
        struct basic_block *parents[3];
        struct basic_block *bb, *bb1, *bb2, *source;
        struct instruction *br;
        pseudo_t p1, p2;

        bb = insn->bb;
        if (get_phisources(array, 2, insn))
                return 0;
        if (linearize_ptr_list((struct ptr_list *)bb->parents, (void **)parents, 3) != 2)
                return 0;
        p1 = array[0]->phi_src;
        bb1 = array[0]->bb;
        p2 = array[1]->phi_src;
        bb2 = array[1]->bb;

        /* Only try the simple "direct parents" case */
        if ((bb1 != parents[0] || bb2 != parents[1]) &&
            (bb1 != parents[1] || bb2 != parents[0]))
                return 0;

        /*
         * See if we can find a common source for this..
         */
        source = phi_parent(bb1, p1);
        if (source != phi_parent(bb2, p2))
                return 0;

        /*
         * Cool. We now know that 'source' is the exclusive
         * parent of both phi-nodes, so the exit at the
         * end of it fully determines which one it is, and
         * we can turn it into a select.
         *
         * HOWEVER, right now we only handle regular
         * conditional branches. No multijumps or computed
         * stuff. Verify that here.
         */
        br = last_instruction(source->insns);
        if (!br || br->opcode != OP_CBR)
                return 0;

        assert(br->cond);
        assert(br->bb_false);

        /*
         * We're in business. Match up true/false with p1/p2.
         */
        if (br->bb_true == bb2 || br->bb_false == bb1) {
                pseudo_t p = p1;
                p1 = p2;
                p2 = p;
        }

        /*
         * OK, we can now replace that last
         *
         *      br cond, a, b
         *
         * with the sequence
         *
         *      setcc cond
         *      select pseudo, p1, p2
         *      br cond, a, b
         *
         * and remove the phi-node. If it then
         * turns out that 'a' or 'b' is entirely
         * empty (common case), and now no longer
         * a phi-source, we'll be able to simplify
         * the conditional branch too.
         */
        insert_select(source, br, insn, p1, p2);
        kill_instruction(insn);
        return REPEAT_CSE;
}

///
// detect trivial phi-nodes
// @insn: the phi-node
// @pseudo: the candidate resulting pseudo (NULL when starting)
// @return: the unique result if the phi-node is trivial, NULL otherwise
//
// A phi-node is trivial if it has a single possible result:
//      * all operands are the same
//      * the operands are themselves defined by a chain or cycle of phi-nodes
//              and the set of all operands involved contains a single value
//              not defined by these phi-nodes
//
// Since the result is unique, these phi-nodes can be removed.
static pseudo_t trivial_phi(pseudo_t pseudo, struct instruction *insn, struct pseudo_list **list)
{
        pseudo_t target = insn->target;
        pseudo_t phi;

        add_pseudo(list, target);

        FOR_EACH_PTR(insn->phi_list, phi) {
                struct instruction *def;
                pseudo_t src;

                if (phi == VOID)
                        continue;
                def = phi->def;
                if (!def->bb)
                        continue;
                src = def->phi_src; // bypass OP_PHISRC & get the real source
                if (src == VOID)
                        continue;
                if (src == target)
                        continue;
                if (!pseudo) {
                        pseudo = src;
                        continue;
                }
                if (src == pseudo)
                        continue;
                if (DEF_OPCODE(def, src) == OP_PHI) {
                        if (pseudo_in_list(*list, src))
                                continue;
                        if ((pseudo = trivial_phi(pseudo, def, list)))
                                continue;
                }
                return NULL;
        } END_FOR_EACH_PTR(phi);

        return pseudo ? pseudo : VOID;
}

static int clean_up_phi(struct instruction *insn)
{
        struct pseudo_list *list = NULL;
        pseudo_t pseudo;

        if ((pseudo = trivial_phi(NULL, insn, &list))) {
                convert_instruction_target(insn, pseudo);
                kill_instruction(insn);
                return REPEAT_CSE;
        }

        return if_convert_phi(insn);
}

static int delete_pseudo_user_list_entry(struct pseudo_user_list **list, pseudo_t *entry, int count)
{
        struct pseudo_user *pu;

        FOR_EACH_PTR(*list, pu) {
                if (pu->userp == entry) {
                        MARK_CURRENT_DELETED(pu);
                        if (!--count)
                                goto out;
                }
        } END_FOR_EACH_PTR(pu);
        assert(count <= 0);
out:
        if (pseudo_user_list_empty(*list))
                *list = NULL;
        return count;
}

static inline void rem_usage(pseudo_t p, pseudo_t *usep, int kill)
{
        if (has_use_list(p)) {
                delete_pseudo_user_list_entry(&p->users, usep, 1);
                if (kill && !p->users && has_definition(p))
                        kill_instruction(p->def);
        }
}

static inline void remove_usage(pseudo_t p, pseudo_t *usep)
{
        rem_usage(p, usep, 1);
}

void kill_use(pseudo_t *usep)
{
        if (usep) {
                pseudo_t p = *usep;
                *usep = VOID;
                rem_usage(p, usep, 1);
        }
}

// Like kill_use() but do not (recursively) kill dead instructions
void remove_use(pseudo_t *usep)
{
        pseudo_t p = *usep;
        *usep = VOID;
        rem_usage(p, usep, 0);
}

static void kill_use_list(struct pseudo_list *list)
{
        pseudo_t p;
        FOR_EACH_PTR(list, p) {
                if (p == VOID)
                        continue;
                kill_use(THIS_ADDRESS(p));
        } END_FOR_EACH_PTR(p);
}

static void kill_asm(struct instruction *insn)
{
        struct asm_constraint *con;

        FOR_EACH_PTR(insn->asm_rules->inputs, con) {
                kill_use(&con->pseudo);
        } END_FOR_EACH_PTR(con);
}

///
// kill an instruction
// @insn: the instruction to be killed
// @force: if unset, the normal case, the instruction is not killed
//      if not free of possible side-effect; if set the instruction
//      is unconditionally killed.
//
// The killed instruction is removed from its BB and the usage
// of all its operands are removed. The instruction is also
// marked as killed by setting its ->bb to NULL.
int kill_insn(struct instruction *insn, int force)
{
        if (!insn || !insn->bb)
                return 0;

        switch (insn->opcode) {
        case OP_SEL:
        case OP_RANGE:
                kill_use(&insn->src3);
                /* fall through */

        case OP_BINARY ... OP_BINCMP_END:
                kill_use(&insn->src2);
                /* fall through */

        case OP_UNOP ... OP_UNOP_END:
        case OP_SLICE:
        case OP_PHISOURCE:
        case OP_SYMADDR:
        case OP_CBR:
        case OP_SWITCH:
        case OP_COMPUTEDGOTO:
                kill_use(&insn->src1);
                break;

        case OP_PHI:
                kill_use_list(insn->phi_list);
                break;

        case OP_CALL:
                if (!force) {
                        /* a "pure" function can be killed too */
                        struct symbol *fntype = first_symbol(insn->fntypes);

                        if (!(fntype->ctype.modifiers & MOD_PURE))
                                return 0;
                }
                kill_use_list(insn->arguments);
                if (insn->func->type == PSEUDO_REG)
                        kill_use(&insn->func);
                break;

        case OP_LOAD:
                if (!force && insn->is_volatile)
                        return 0;
                kill_use(&insn->src);
                break;

        case OP_STORE:
                if (!force)
                        return 0;
                kill_use(&insn->src);
                kill_use(&insn->target);
                break;

        case OP_ASM:
                if (!force)
                        return 0;
                kill_asm(insn);
                break;

        case OP_ENTRY:
                /* ignore */
                return 0;

        case OP_BR:
        case OP_LABEL:
        case OP_SETVAL:
        case OP_SETFVAL:
        default:
                break;
        }

        insn->bb = NULL;
        return repeat_phase |= REPEAT_CSE;
}

static inline bool has_target(struct instruction *insn)
{
        return opcode_table[insn->opcode].flags & OPF_TARGET;
}

void remove_dead_insns(struct entrypoint *ep)
{
        struct basic_block *bb;

        FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
                struct instruction *insn;
                FOR_EACH_PTR_REVERSE(bb->insns, insn) {
                        if (!insn->bb)
                                continue;
                        if (!has_target(insn))
                                continue;
                        if (!has_users(insn->target))
                                kill_instruction(insn);
                } END_FOR_EACH_PTR_REVERSE(insn);
        } END_FOR_EACH_PTR_REVERSE(bb);
}

static inline int constant(pseudo_t pseudo)
{
        return pseudo->type == PSEUDO_VAL;
}

///
// is this same signed value when interpreted with both size?
static inline bool is_signed_constant(long long val, unsigned osize, unsigned nsize)
{
        return bits_extend(val, osize, 1) == bits_extend(val, nsize, 1);
}

///
// is @src generated by an instruction with the given opcode and size?
static inline pseudo_t is_same_op(pseudo_t src, int op, unsigned osize)
{
        struct instruction *def;

        if (src->type != PSEUDO_REG)
                return NULL;
        def = src->def;
        if (def->opcode != op)
                return NULL;
        if (def->orig_type->bit_size != osize)
                return NULL;
        return def->src;
}

///
// replace the operand of an instruction
// @insn: the instruction
// @pp: the address of the instruction's operand
// @new: the new value for the operand
// @return: REPEAT_CSE.
static inline int replace_pseudo(struct instruction *insn, pseudo_t *pp, pseudo_t new)
{
        pseudo_t old = *pp;
        use_pseudo(insn, new, pp);
        remove_usage(old, pp);
        return REPEAT_CSE;
}

int replace_with_pseudo(struct instruction *insn, pseudo_t pseudo)
{
        convert_instruction_target(insn, pseudo);
        return kill_instruction(insn);
}

static inline int replace_with_value(struct instruction *insn, long long val)
{
        return replace_with_pseudo(insn, value_pseudo(val));
}

///
// replace a binop with an unop
// @insn: the instruction to be replaced
// @op: the instruction's new opcode
// @src: the instruction's new operand
// @return: REPEAT_CSE
static inline int replace_with_unop(struct instruction *insn, int op, pseudo_t src)
{
        insn->opcode = op;
        replace_pseudo(insn, &insn->src1, src);
        remove_usage(insn->src2, &insn->src2);
        return REPEAT_CSE;
}

///
// replace rightside's value
// @insn: the instruction to be replaced
// @op: the instruction's new opcode
// @src: the instruction's new operand
// @return: REPEAT_CSE
static inline int replace_binop_value(struct instruction *insn, int op, long long val)
{
        insn->opcode = op;
        insn->src2 = value_pseudo(val);
        return REPEAT_CSE;
}

///
// replace binop's opcode and values
// @insn: the instruction to be replaced
// @op: the instruction's new opcode
// @return: REPEAT_CSE
static inline int replace_binop(struct instruction *insn, int op, pseudo_t *pa, pseudo_t a, pseudo_t *pb, pseudo_t b)
{
        pseudo_t olda = *pa;
        pseudo_t oldb = *pb;
        insn->opcode = op;
        use_pseudo(insn, a, pa);
        use_pseudo(insn, b, pb);
        remove_usage(olda, pa);
        remove_usage(oldb, pb);
        return REPEAT_CSE;
}

///
// replace the opcode of an instruction
// @return: REPEAT_CSE
static inline int replace_opcode(struct instruction *insn, int op)
{
        insn->opcode = op;
        return REPEAT_CSE;
}

///
// create an instruction pair OUT(IN(a, b), c)
static int replace_insn_pair(struct instruction *out, int op_out, struct instruction *in, int op_in, pseudo_t a, pseudo_t b, pseudo_t c)
{
        pseudo_t old_a = in->src1;
        pseudo_t old_b = in->src2;
        pseudo_t old_1 = out->src1;
        pseudo_t old_2 = out->src2;

        use_pseudo(in, a, &in->src1);
        use_pseudo(in, b, &in->src2);
        use_pseudo(out, in->target, &out->src1);
        use_pseudo(out, c, &out->src2);

        remove_usage(old_a, &in->src1);
        remove_usage(old_b, &in->src2);
        remove_usage(old_1, &out->src1);
        remove_usage(old_2, &out->src2);

        out->opcode = op_out;
        in->opcode = op_in;
        return REPEAT_CSE;
}

///
// create an instruction pair OUT(IN(a, b), c) with swapped opcodes
static inline int swap_insn(struct instruction *out, struct instruction *in, pseudo_t a, pseudo_t b, pseudo_t c)
{
        return replace_insn_pair(out, in->opcode, in, out->opcode, a, b, c);
}

///
// create an instruction pair OUT(SELECT(a, b, c), d)
static int swap_select(struct instruction *out, struct instruction *in, pseudo_t a, pseudo_t b, pseudo_t c, pseudo_t d)
{
        use_pseudo(in, c, &in->src3);
        swap_insn(out, in, a, b, d);
        kill_use(&out->src3);
        return REPEAT_CSE;
}

static inline int def_opcode(pseudo_t p)
{
        if (p->type != PSEUDO_REG)
                return OP_BADOP;
        return p->def->opcode;
}

static unsigned int value_size(long long value)
{
        value >>= 8;
        if (!value)
                return 8;
        value >>= 8;
        if (!value)
                return 16;
        value >>= 16;
        if (!value)
                return 32;
        return 64;
}

///
// try to determine the maximum size of bits in a pseudo
//
// Right now this only follow casts and constant values, but we
// could look at things like AND instructions, etc.
static unsigned int operand_size(struct instruction *insn, pseudo_t pseudo)
{
        unsigned int size = insn->size;

        if (pseudo->type == PSEUDO_REG) {
                struct instruction *src = pseudo->def;
                if (src && src->opcode == OP_ZEXT && src->orig_type) {
                        unsigned int orig_size = src->orig_type->bit_size;
                        if (orig_size < size)
                                size = orig_size;
                }
        }
        if (pseudo->type == PSEUDO_VAL) {
                unsigned int orig_size = value_size(pseudo->value);
                if (orig_size < size)
                        size = orig_size;
        }
        return size;
}

static pseudo_t eval_op(int op, unsigned size, pseudo_t src1, pseudo_t src2)
{
        /* FIXME! Verify signs and sizes!! */
        long long left = src1->value;
        long long right = src2->value;
        unsigned long long ul, ur;
        long long res, mask, bits;

        mask = 1ULL << (size-1);
        bits = mask | (mask-1);

        if (left & mask)
                left |= ~bits;
        if (right & mask)
                right |= ~bits;
        ul = left & bits;
        ur = right & bits;

        switch (op) {
        case OP_NEG:
                res = -left;
                break;
        case OP_NOT:
                res = ~ul;
                break;

        case OP_ADD:
                res = left + right;
                break;
        case OP_SUB:
                res = left - right;
                break;
        case OP_MUL:
                res = ul * ur;
                break;
        case OP_DIVU:
                if (!ur)
                        goto undef;
                res = ul / ur;
                break;
        case OP_DIVS:
                if (!right)
                        goto undef;
                if (left == mask && right == -1)
                        goto undef;
                res = left / right;
                break;
        case OP_MODU:
                if (!ur)
                        goto undef;
                res = ul % ur;
                break;
        case OP_MODS:
                if (!right)
                        goto undef;
                if (left == mask && right == -1)
                        goto undef;
                res = left % right;
                break;
        case OP_SHL:
                if (ur >= size)
                        goto undef;
                res = left << right;
                break;
        case OP_LSR:
                if (ur >= size)
                        goto undef;
                res = ul >> ur;
                break;
        case OP_ASR:
                if (ur >= size)
                        goto undef;
                res = left >> right;
                break;
       /* Logical */
        case OP_AND:
                res = left & right;
                break;
        case OP_OR:
                res = left | right;
                break;
        case OP_XOR:
                res = left ^ right;
                break;

        /* Binary comparison */
        case OP_SET_EQ:
                res = left == right;
                break;
        case OP_SET_NE:
                res = left != right;
                break;
        case OP_SET_LE:
                res = left <= right;
                break;
        case OP_SET_GE:
                res = left >= right;
                break;
        case OP_SET_LT:
                res = left < right;
                break;
        case OP_SET_GT:
                res = left > right;
                break;
        case OP_SET_B:
                res = ul < ur;
                break;
        case OP_SET_A:
                res = ul > ur;
                break;
        case OP_SET_BE:
                res = ul <= ur;
                break;
        case OP_SET_AE:
                res = ul >= ur;
                break;
        default:
                return NULL;
        }

        // Warning: this should be done with the output size which may
        // be different than the input size used here. But it differs
        // only for compares which are not concerned since only returning
        // 0 or 1 and for casts which are not handled here.
        res &= bits;

        return value_pseudo(res);

undef:
        return NULL;
}

static inline pseudo_t eval_unop(int op, unsigned size, pseudo_t src)
{
        return eval_op(op, size, src, VOID);
}

///
// Simplifications
// ^^^^^^^^^^^^^^^

///
// try to simplify MASK(OR(AND(x, M'), b), M)
// @insn: the masking instruction
// @mask: the associated mask (M)
// @ora: one of the OR's operands, guaranteed to be PSEUDO_REG
// @orb: the other OR's operand
// @return: 0 if no changes have been made, one or more REPEAT_* flags otherwise.
static int simplify_mask_or_and(struct instruction *insn, unsigned long long mask,
        pseudo_t ora, pseudo_t orb)
{
        unsigned long long omask, nmask;
        struct instruction *and = ora->def;
        pseudo_t src2 = and->src2;

        if (and->opcode != OP_AND)
                return 0;
        if (!constant(src2))
                return 0;
        omask = src2->value;
        nmask = omask & mask;
        if (nmask == 0) {
                // if (M' & M) == 0: ((a & M') | b) -> b
                return replace_pseudo(insn, &insn->src1, orb);
        }
        if (!one_use(insn->src1))
                return 0;       // can't modify anything inside the OR
        if (nmask == mask) {
                struct instruction *or = insn->src1->def;
                pseudo_t *arg = (ora == or->src1) ? &or->src1 : &or->src2;
                // if (M' & M) == M: ((a & M') | b) -> (a | b)
                return replace_pseudo(or, arg, and->src1);
        }
        if (nmask != omask && one_use(ora)) {
                // if (M' & M) != M': AND(a, M') -> AND(a, (M' & M))
                and->src2 = value_pseudo(nmask);
                return REPEAT_CSE;
        }
        return 0;
}

///
// try to simplify MASK(OR(a, b), M)
// @insn: the masking instruction
// @mask: the associated mask (M)
// @or: the OR instruction
// @return: 0 if no changes have been made, one or more REPEAT_* flags otherwise.
static int simplify_mask_or(struct instruction *insn, unsigned long long mask, struct instruction *or)
{
        pseudo_t src1 = or->src1;
        pseudo_t src2 = or->src2;
        int rc;

        if (src1->type == PSEUDO_REG) {
                if ((rc = simplify_mask_or_and(insn, mask, src1, src2)))
                        return rc;
        }
        if (src2->type == PSEUDO_REG) {
                if ((rc = simplify_mask_or_and(insn, mask, src2, src1)))
                        return rc;
        } else if (src2->type == PSEUDO_VAL) {
                unsigned long long oval = src2->value;
                unsigned long long nval = oval & mask;
                // Try to simplify:
                //      MASK(OR(x, C), M)
                if (nval == 0) {
                        // if (C & M) == 0: OR(x, C) -> x
                        return replace_pseudo(insn, &insn->src1, src1);
                }
                if (nval == mask) {
                        // if (C & M) == M: OR(x, C) -> M
                        return replace_pseudo(insn, &insn->src1, value_pseudo(mask));
                }
                if (nval != oval && one_use(or->target)) {
                        // if (C & M) != C: OR(x, C) -> OR(x, (C & M))
                        return replace_pseudo(or, &or->src2, value_pseudo(nval));
                }
        }
        return 0;
}

///
// try to simplify MASK(SHIFT(OR(a, b), S), M)
// @sh: the shift instruction
// @or: the OR instruction
// @mask: the mask associated to MASK (M):
// @return: 0 if no changes have been made, one or more REPEAT_* flags otherwise.
static int simplify_mask_shift_or(struct instruction *sh, struct instruction *or, unsigned long long mask)
{
        unsigned long long smask = bits_mask(sh->size);
        int shift = sh->src2->value;

        if (sh->opcode == OP_LSR)
                mask <<= shift;
        else
                mask >>= shift;
        return simplify_mask_or(sh, smask & mask, or);
}

static int simplify_mask_shift(struct instruction *sh, unsigned long long mask)
{
        struct instruction *inner;

        if (!constant(sh->src2) || sh->tainted)
                return 0;
        switch (DEF_OPCODE(inner, sh->src1)) {
        case OP_OR:
                if (one_use(sh->target))
                        return simplify_mask_shift_or(sh, inner, mask);
                break;
        }
        return 0;
}

static pseudo_t eval_insn(struct instruction *insn)
{
        unsigned size = insn->size;

        if (opcode_table[insn->opcode].flags & OPF_COMPARE)
                size = insn->itype->bit_size;
        return eval_op(insn->opcode, size, insn->src1, insn->src2);
}

static long long check_shift_count(struct instruction *insn, unsigned long long uval)
{
        unsigned int size = insn->size;
        long long sval = uval;

        if (insn->tainted)
                return -1;

        if (uval < size)
                return uval;

        insn->tainted = 1;
        sval = sign_extend_safe(sval, size);
        sval = sign_extend_safe(sval, bits_in_int);
        if (sval < 0)
                insn->src2 = value_pseudo(sval);
        return -1;
}

static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long value)
{
        struct instruction *def;
        unsigned long long mask, omask, nmask;
        unsigned long long nval;
        unsigned int size;
        pseudo_t src2;

        if (!value)
                return replace_with_pseudo(insn, pseudo);
        value = check_shift_count(insn, value);
        if (value < 0)
                return 0;

        size = insn->size;
        switch (insn->opcode) {
        case OP_ASR:
                if (value >= size)
                        return 0;
                if (pseudo->type != PSEUDO_REG)
                        break;
                def = pseudo->def;
                switch (def->opcode) {
                case OP_LSR:
                case OP_ASR:
                        if (def == insn)        // cyclic DAG!
                                break;
                        src2 = def->src2;
                        if (src2->type != PSEUDO_VAL)
                                break;
                        nval = src2->value;
                        if (nval > insn->size || nval == 0)
                                break;
                        value += nval;
                        if (def->opcode == OP_LSR)
                                insn->opcode = OP_LSR;
                        else if (value >= size)
                                value = size - 1;
                        goto new_value;

                case OP_ZEXT:
                        // transform:
                        //      zext.N  %t <- (O) %a
                        //      asr.N   %r <- %t, C
                        // into
                        //      zext.N  %t <- (O) %a
                        //      lsr.N   %r <- %t, C
                        insn->opcode = OP_LSR;
                        return REPEAT_CSE;
                }
                break;
        case OP_LSR:
                size = operand_size(insn, pseudo);
                if (value >= size)
                        goto zero;
                switch(DEF_OPCODE(def, pseudo)) {
                case OP_AND:
                        // replace (A & M) >> S
                        // by      (A >> S) & (M >> S)
                        if (!constant(def->src2))
                                break;
                        mask = bits_mask(insn->size - value) << value;
                        omask = def->src2->value;
                        nmask = omask & mask;
                        if (nmask == 0)
                                return replace_with_value(insn, 0);
                        if (nmask == mask)
                                return replace_pseudo(insn, &insn->src1, def->src1);
                        if (!one_use(pseudo))
                                break;
                        def->opcode = OP_LSR;
                        def->src2 = insn->src2;
                        insn->opcode = OP_AND;
                        insn->src2 = value_pseudo(omask >> value);
                        return REPEAT_CSE;
                case OP_LSR:
                        goto case_shift_shift;
                case OP_OR:
                        mask = bits_mask(size);
                        return simplify_mask_shift_or(insn, def, mask);
                case OP_SHL:
                        // replace ((x << S) >> S)
                        // by      (x & (-1 >> S))
                        if (def->src2 != insn->src2)
                                break;
                        mask = bits_mask(insn->size - value);
                        goto replace_mask;
                }
                break;
        case OP_SHL:
                if (value >= size)
                        goto zero;
                switch(DEF_OPCODE(def, pseudo)) {
                case OP_AND:
                        // simplify (A & M) << S
                        if (!constant(def->src2))
                                break;
                        mask = bits_mask(insn->size) >> value;
                        omask = def->src2->value;
                        nmask = omask & mask;
                        if (nmask == 0)
                                return replace_with_value(insn, 0);
                        if (nmask == mask)
                                return replace_pseudo(insn, &insn->src1, def->src1);
                        // do not simplify into ((A << S) & (M << S))
                        break;
                case OP_LSR:
                        // replace ((x >> S) << S)
                        // by      (x & (-1 << S))
                        if (def->src2 != insn->src2)
                                break;
                        mask = bits_mask(insn->size - value) << value;
                        goto replace_mask;
                case OP_OR:
                        mask = bits_mask(size);
                        return simplify_mask_shift_or(insn, def, mask);
                case OP_SHL:
                case_shift_shift:               // also for LSR - LSR
                        if (def == insn)        // cyclic DAG!
                                break;
                        src2 = def->src2;
                        if (src2->type != PSEUDO_VAL)
                                break;
                        nval = src2->value;
                        if (nval > insn->size)
                                break;
                        value += nval;
                        goto new_value;
                }
                break;
        }
        return 0;

new_value:
        if (value < size) {
                insn->src2 = value_pseudo(value);
                return replace_pseudo(insn, &insn->src1, pseudo->def->src1);
        }
zero:
        return replace_with_value(insn, 0);
replace_mask:
        insn->opcode = OP_AND;
        insn->src2 = value_pseudo(mask);
        return replace_pseudo(insn, &insn->src1, def->src1);
}

static int simplify_mul_div(struct instruction *insn, long long value)
{
        unsigned long long sbit = 1ULL << (insn->size - 1);
        unsigned long long bits = sbit | (sbit - 1);

        if (value == 1)
                return replace_with_pseudo(insn, insn->src1);

        switch (insn->opcode) {
        case OP_MUL:
                if (value == 0)
                        return replace_with_pseudo(insn, insn->src2);
        /* Fall through */
        case OP_DIVS:
                if (!(value & sbit))    // positive
                        break;

                value |= ~bits;
                if (value == -1) {
                        insn->opcode = OP_NEG;
                        return REPEAT_CSE;
                }
        }

        return 0;
}

static int simplify_seteq_setne(struct instruction *insn, long long value)
{
        pseudo_t old = insn->src1;
        struct instruction *def;
        unsigned osize;
        int inverse;
        int opcode;

        if (value != 0 && value != 1)
                return 0;

        if (old->type != PSEUDO_REG)
                return 0;
        def = old->def;
        if (!def)
                return 0;

        inverse = (insn->opcode == OP_SET_NE) == value;
        if (!inverse && def->size == 1 && insn->size == 1) {
                // Replace:
                //      setne   %r <- %s, $0
                // or:
                //      seteq   %r <- %s, $1
                // by %s when boolean
                return replace_with_pseudo(insn, old);
        }
        opcode = def->opcode;
        switch (opcode) {
        case OP_AND:
                if (inverse)
                        break;
                if (def->size != insn->size)
                        break;
                if (def->src2->type != PSEUDO_VAL)
                        break;
                if (def->src2->value != 1)
                        break;
                return replace_with_pseudo(insn, old);
        case OP_FPCMP ... OP_BINCMP_END:
                // Convert:
                //      setcc.n %t <- %a, %b
                //      setne.m %r <- %t, $0
                // into:
                //      setcc.n %t <- %a, %b
                //      setcc.m %r <- %a, $b
                // and similar for setne/eq ... 0/1
                insn->opcode = inverse ? opcode_table[opcode].negate : opcode;
                insn->itype = def->itype;
                use_pseudo(insn, def->src1, &insn->src1);
                use_pseudo(insn, def->src2, &insn->src2);
                remove_usage(old, &insn->src1);
                return REPEAT_CSE;

        case OP_SEXT:
                if (value && (def->orig_type->bit_size == 1))
                        break;
                /* Fall through */
        case OP_ZEXT:
                // Convert:
                //      *ext.m  %s <- (1) %a
                //      setne.1 %r <- %s, $0
                // into:
                //      setne.1 %s <- %a, $0
                // and same for setne/eq ... 0/1
                insn->itype = def->orig_type;
                return replace_pseudo(insn, &insn->src1, def->src);
        case OP_TRUNC:
                if (!one_use(old))
                        break;
                // convert
                //      trunc.n %s <- (o) %a
                //      setne.m %r <- %s, $0
                // into:
                //      and.o   %s <- %a, $((1 << o) - 1)
                //      setne.m %r <- %s, $0
                // and same for setne/eq ... 0/1
                osize = def->size;
                def->opcode = OP_AND;
                def->type = def->orig_type;
                def->size = def->type->bit_size;
                def->src2 = value_pseudo(bits_mask(osize));
                return REPEAT_CSE;
        }
        return 0;
}

static int simplify_compare_constant(struct instruction *insn, long long value)
{
        unsigned long long bits = bits_mask(insn->itype->bit_size);
        struct instruction *def;
        pseudo_t src1, src2;
        unsigned int osize;
        int changed = 0;

        switch (insn->opcode) {
        case OP_SET_B:
                if (!value)                     // (x < 0) --> 0
                        return replace_with_pseudo(insn, value_pseudo(0));
                if (value == 1)                 // (x < 1) --> (x == 0)
                        return replace_binop_value(insn, OP_SET_EQ, 0);
                else if (value == bits)         // (x < ~0) --> (x != ~0)
                        return replace_binop_value(insn, OP_SET_NE, value);
                else                            // (x < y) --> (x <= (y-1))
                        changed |= replace_binop_value(insn, OP_SET_BE, value - 1);
                break;
        case OP_SET_AE:
                if (!value)                     // (x >= 0) --> 1
                        return replace_with_pseudo(insn, value_pseudo(1));
                if (value == 1)                 // (x >= 1) --> (x != 0)
                        return replace_binop_value(insn, OP_SET_NE, 0);
                else if (value == bits)         // (x >= ~0) --> (x == ~0)
                        return replace_binop_value(insn, OP_SET_EQ, value);
                else                            // (x >= y) --> (x > (y-1)
                        changed |= replace_binop_value(insn, OP_SET_A, value - 1);
                break;
        case OP_SET_BE:
                if (!value)                     // (x <= 0) --> (x == 0)
                        return replace_opcode(insn, OP_SET_EQ);
                if (value == bits)              // (x <= ~0) --> 1
                        return replace_with_pseudo(insn, value_pseudo(1));
                if (value == (bits - 1))        // (x <= ~1) --> (x != ~0)
                        return replace_binop_value(insn, OP_SET_NE, bits);
                if (value == (bits >> 1))       // (x u<= SMAX) --> (x s>= 0)
                        changed |= replace_binop_value(insn, OP_SET_GE, 0);
                break;
        case OP_SET_A:
                if (!value)                     // (x > 0) --> (x != 0)
                        return replace_opcode(insn, OP_SET_NE);
                if (value == bits)              // (x > ~0) --> 0
                        return replace_with_pseudo(insn, value_pseudo(0));
                if (value == (bits - 1))        // (x > ~1) --> (x == ~0)
                        return replace_binop_value(insn, OP_SET_EQ, bits);
                if (value == (bits >> 1))       // (x u> SMAX) --> (x s< 0)
                        changed |= replace_binop_value(insn, OP_SET_LT, 0);
                break;
        }

        src1 = insn->src1;
        src2 = insn->src2;
        value = src2->value;
        switch (DEF_OPCODE(def, src1)) {
        case OP_SEXT:                           // sext(x) cmp C --> x cmp trunc(C)
                osize = def->orig_type->bit_size;
                if (is_signed_constant(value, osize, def->size)) {
                        insn->itype = def->orig_type;
                        insn->src2 = value_pseudo(zero_extend(value, osize));
                        return replace_pseudo(insn, &insn->src1, def->src);
                }
                switch (insn->opcode) {
                case OP_SET_BE:
                        if (value >= sign_bit(osize)) {
                                replace_binop_value(insn, OP_SET_GE, 0);
                                return replace_pseudo(insn, &insn->src1, def->src);
                        }
                        break;
                case OP_SET_A:
                        if (value >= sign_bit(osize)) {
                                replace_binop_value(insn, OP_SET_LT, 0);
                                return replace_pseudo(insn, &insn->src1, def->src);
                        }
                        break;
                case OP_SET_LT: case OP_SET_LE:
                        if (value >= sign_bit(osize))
                                return replace_with_value(insn, 1);
                        else
                                return replace_with_value(insn, 0);
                        break;
                case OP_SET_GE: case OP_SET_GT:
                        if (value >= sign_bit(osize))
                                return replace_with_value(insn, 0);
                        else
                                return replace_with_value(insn, 1);
                        break;
                }
                break;
        case OP_ZEXT:
                osize = def->orig_type->bit_size;
                bits = bits_mask(osize);
                if (value <= bits) {
                        const struct opcode_table *op = &opcode_table[insn->opcode];
                        if (op->flags & OPF_SIGNED)
                                insn->opcode = op->sign;
                        insn->itype = def->orig_type;
                        return replace_pseudo(insn, &insn->src1, def->src);
                }
                switch (insn->opcode) {
                case OP_SET_LT: case OP_SET_LE:
                        if (sign_extend(value, def->size) > (long long)bits)
                                return replace_with_value(insn, 1);
                        else
                                return replace_with_value(insn, 0);
                        break;
                case OP_SET_GE: case OP_SET_GT:
                        if (sign_extend(value, def->size) > (long long)bits)
                                return replace_with_value(insn, 0);
                        else
                                return replace_with_value(insn, 1);
                        break;
                case OP_SET_B: case OP_SET_BE:
                        return replace_with_value(insn, 1);
                case OP_SET_AE: case OP_SET_A:
                        return replace_with_value(insn, 0);
                }
                break;
        }
        return changed;
}

static int simplify_constant_mask(struct instruction *insn, unsigned long long mask)
{
        pseudo_t old = insn->src1;
        unsigned long long omask;
        unsigned long long nmask;
        struct instruction *def;
        int osize;

        switch (DEF_OPCODE(def, old)) {
        case OP_FPCMP ... OP_BINCMP_END:
                osize = 1;
                goto oldsize;
        case OP_OR:
                return simplify_mask_or(insn, mask, def);
        case OP_LSR:
        case OP_SHL:
                return simplify_mask_shift(def, mask);
        case OP_ZEXT:
                osize = def->orig_type->bit_size;
                /* fall through */
        oldsize:
                omask = (1ULL << osize) - 1;
                nmask = mask & omask;
                if (nmask == omask)
                        // the AND mask is redundant
                        return replace_with_pseudo(insn, old);
                if (nmask != mask) {
                        // can use a smaller mask
                        insn->src2 = value_pseudo(nmask);
                        return REPEAT_CSE;
                }
                break;
        }
        return 0;
}

static int simplify_const_rightadd(struct instruction *def, struct instruction *insn)
{
        unsigned size = insn->size;
        pseudo_t src2 = insn->src2;

        switch (def->opcode) {
        case OP_SUB:
                if (constant(def->src1)) { // (C - y) + D --> eval(C+D) - y
                        pseudo_t val = eval_op(OP_ADD, size, def->src1, src2);
                        insn->opcode = OP_SUB;
                        use_pseudo(insn, def->src2, &insn->src2);
                        return replace_pseudo(insn, &insn->src1, val);
                }
                break;
        }
        return 0;
}

static int simplify_constant_rightside(struct instruction *insn)
{
        long long value = insn->src2->value;
        long long sbit = 1ULL << (insn->size - 1);
        long long bits = sbit | (sbit - 1);
        int changed = 0;

        switch (insn->opcode) {
        case OP_OR:
                if ((value & bits) == bits)
                        return replace_with_pseudo(insn, insn->src2);
                goto case_neutral_zero;

        case OP_XOR:
                if ((value & bits) == bits) {
                        insn->opcode = OP_NOT;
                        return REPEAT_CSE;
                }
                /* fallthrough */
        case_neutral_zero:
                if (!value)
                        return replace_with_pseudo(insn, insn->src1);
                return 0;

        case OP_SUB:
                insn->opcode = OP_ADD;
                insn->src2 = eval_unop(OP_NEG, insn->size, insn->src2);
                changed = REPEAT_CSE;
                /* fallthrough */
        case OP_ADD:
                if (!value)
                        return replace_with_pseudo(insn, insn->src1);
                if (insn->src1->type == PSEUDO_REG)     // (x # y) + z
                        changed |= simplify_const_rightadd(insn->src1->def, insn);
                return changed;
        case OP_ASR:
        case OP_SHL:
        case OP_LSR:
                return simplify_shift(insn, insn->src1, value);

        case OP_MODU: case OP_MODS:
                if (value == 1)
                        return replace_with_value(insn, 0);
                return 0;

        case OP_DIVU: case OP_DIVS:
        case OP_MUL:
                return simplify_mul_div(insn, value);

        case OP_AND:
                if (!value)
                        return replace_with_pseudo(insn, insn->src2);
                if ((value & bits) == bits)
                        return replace_with_pseudo(insn, insn->src1);
                return simplify_constant_mask(insn, value);

        case OP_SET_NE:
        case OP_SET_EQ:
                if ((changed = simplify_seteq_setne(insn, value)))
                        return changed;
                /* fallthrough */
        case OP_SET_LT: case OP_SET_LE: case OP_SET_GE: case OP_SET_GT:
        case OP_SET_B:  case OP_SET_BE: case OP_SET_AE: case OP_SET_A:
                return simplify_compare_constant(insn, value);
        }
        return 0;
}

static int simplify_const_leftsub(struct instruction *insn, struct instruction *def)
{
        unsigned size = insn->size;
        pseudo_t src1 = insn->src1;

        switch (def->opcode) {
        case OP_ADD:
                if (constant(def->src2)) { // C - (y + D) --> eval(C-D) - y
                        insn->src1 = eval_op(OP_SUB, size, src1, def->src2);
                        return replace_pseudo(insn, &insn->src2, def->src1);
                }
                break;
        case OP_SUB:
                if (constant(def->src1)) { // C - (D - z) --> z + eval(C-D)
                        pseudo_t val = eval_op(OP_SUB, size, src1, def->src1);
                        insn->opcode = OP_ADD;
                        use_pseudo(insn, def->src2, &insn->src1);
                        return replace_pseudo(insn, &insn->src2, val);
                }
                break;
        }
        return 0;
}

static int simplify_constant_leftside(struct instruction *insn)
{
        long long value = insn->src1->value;

        switch (insn->opcode) {
        case OP_ADD: case OP_OR: case OP_XOR:
                if (!value)
                        return replace_with_pseudo(insn, insn->src2);
                return 0;

        case OP_SHL:
        case OP_LSR: case OP_ASR:
        case OP_AND:
        case OP_MUL:
                if (!value)
                        return replace_with_pseudo(insn, insn->src1);
                return 0;
        case OP_SUB:
                if (!value)                     // (0 - x) --> -x
                        return replace_with_unop(insn, OP_NEG, insn->src2);
                if (insn->src2->type == PSEUDO_REG)
                        return simplify_const_leftsub(insn, insn->src2->def);
                break;
        }
        return 0;
}

static int simplify_constant_binop(struct instruction *insn)
{
        pseudo_t res = eval_insn(insn);

        if (!res)
                return 0;

        return replace_with_pseudo(insn, res);
}

static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg)
{
        switch (insn->opcode) {
        case OP_SET_NE:
        case OP_SET_LT: case OP_SET_GT:
        case OP_SET_B:  case OP_SET_A:
                if (Wtautological_compare)
                        warning(insn->pos, "self-comparison always evaluates to false");
        case OP_SUB:
        case OP_XOR:
                return replace_with_value(insn, 0);

        case OP_SET_EQ:
        case OP_SET_LE: case OP_SET_GE:
        case OP_SET_BE: case OP_SET_AE:
                if (Wtautological_compare)
                        warning(insn->pos, "self-comparison always evaluates to true");
                return replace_with_value(insn, 1);

        case OP_AND:
        case OP_OR:
                return replace_with_pseudo(insn, arg);

        default:
                break;
        }

        return 0;
}

static int simplify_binop(struct instruction *insn)
{
        if (constant(insn->src1)) {
                if (constant(insn->src2))
                        return simplify_constant_binop(insn);
                return simplify_constant_leftside(insn);
        }
        if (constant(insn->src2))
                return simplify_constant_rightside(insn);
        if (insn->src1 == insn->src2)
                return simplify_binop_same_args(insn, insn->src1);
        return 0;
}

static int switch_pseudo(struct instruction *insn1, pseudo_t *pp1, struct instruction *insn2, pseudo_t *pp2)
{
        pseudo_t p1 = *pp1, p2 = *pp2;

        use_pseudo(insn1, p2, pp1);
        use_pseudo(insn2, p1, pp2);
        remove_usage(p1, pp1);
        remove_usage(p2, pp2);
        return REPEAT_CSE;
}

///
// check if the given pseudos are in canonical order
//
// The canonical order is VOID < UNDEF < PHI < REG < ARG < SYM < VAL
// The rationale is:
//      * VALs at right (they don't need a definition)
//      * REGs at left (they need a defining instruction)
//      * SYMs & ARGs between REGs & VALs
//      * REGs & ARGs are ordered between themselves by their internal number
//      * SYMs are ordered between themselves by address
//      * VOID, UNDEF and PHI are uninteresting (but VOID should have type 0)
static int canonical_order(pseudo_t p1, pseudo_t p2)
{
        int t1 = p1->type;
        int t2 = p2->type;

        /* symbol/constants on the right */
        if (t1 < t2)
                return 1;
        if (t1 > t2)
                return 0;
        switch (t1) {
        case PSEUDO_SYM:
                return p1->sym <= p2->sym;
        case PSEUDO_REG:
        case PSEUDO_ARG:
                return p1->nr <= p2->nr;
        default:
                return 1;
        }
}

static int canonicalize_commutative(struct instruction *insn)
{
        if (canonical_order(insn->src1, insn->src2))
                return 0;

        switch_pseudo(insn, &insn->src1, insn, &insn->src2);
        return repeat_phase |= REPEAT_CSE;
}

static int canonicalize_compare(struct instruction *insn)
{
        if (canonical_order(insn->src1, insn->src2))
                return 0;

        switch_pseudo(insn, &insn->src1, insn, &insn->src2);
        insn->opcode = opcode_table[insn->opcode].swap;
        return repeat_phase |= REPEAT_CSE;
}

static inline int simple_pseudo(pseudo_t pseudo)
{
        return pseudo->type == PSEUDO_VAL || pseudo->type == PSEUDO_SYM;
}

///
// test if, in the given BB, the ordering of 2 instructions
static bool insn_before(struct basic_block *bb, struct instruction *x, struct instruction *y)
{
        struct instruction *insn;

        FOR_EACH_PTR(bb->insns, insn) {
                if (insn == x)
                        return true;
                if (insn == y)
                        return false;
        } END_FOR_EACH_PTR(insn);
        return false;
}

///
// check if it safe for a pseudo to be used by an instruction
static inline bool can_move_to(pseudo_t src, struct instruction *dst)
{
        struct basic_block *bbs, *bbd;
        struct instruction *def;

        if (!one_use(dst->target))
                return false;
        if (src->type != PSEUDO_REG)
                return true;

        def = src->def;
        bbs = def->bb;
        bbd = dst->bb;
        if (bbs == bbd)
                return insn_before(bbs, def, dst);
        else
                return domtree_dominates(bbs, bbd);
}

static int simplify_associative_binop(struct instruction *insn)
{
        struct instruction *def;
        pseudo_t pseudo = insn->src1;

        if (!simple_pseudo(insn->src2))
                return 0;
        if (pseudo->type != PSEUDO_REG)
                return 0;
        def = pseudo->def;
        if (def == insn)
                return 0;
        if (def->opcode != insn->opcode)
                return 0;
        if (!simple_pseudo(def->src2))
                return 0;
        if (constant(def->src2) && constant(insn->src2)) {
                // (x # C) # K --> x # eval(C # K)
                insn->src2 = eval_op(insn->opcode, insn->size, insn->src2, def->src2);
                return replace_pseudo(insn, &insn->src1, def->src1);
        }
        if (!one_use(def->target))
                return 0;
        switch_pseudo(def, &def->src1, insn, &insn->src2);
        return REPEAT_CSE;
}

static int simplify_add_one_side(struct instruction *insn, pseudo_t *p1, pseudo_t *p2)
{
        struct instruction *defr = NULL;
        struct instruction *def;
        pseudo_t src1 = *p1;
        pseudo_t src2 = *p2;

        switch (DEF_OPCODE(def, src1)) {
        case OP_MUL:
                if (DEF_OPCODE(defr, *p2) == OP_MUL) {
                        if (defr->src2 == def->src2 && can_move_to(def->src2, defr)) {
                                // ((x * z) + (y * z)) into ((x + y) * z)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src1 && can_move_to(def->src1, defr)) {
                                // ((z * x) + (z * y)) into ((x + y) * z)
                                swap_insn(insn, defr, def->src2, defr->src2, def->src1);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src2 && can_move_to(def->src1, defr)) {
                                // ((x * z) + (z * y)) into ((x + y) * z)
                                swap_insn(insn, defr, def->src1, defr->src2, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;

        case OP_NEG:                            // (-x + y) --> (y - x)
                return replace_binop(insn, OP_SUB, &insn->src1, src2, &insn->src2, def->src);

        case OP_SUB:
                if (def->src2 == src2)          // (x - y) + y --> x
                        return replace_with_pseudo(insn, def->src1);
                break;
        }
        return 0;
}

static int simplify_add(struct instruction *insn)
{
        return simplify_add_one_side(insn, &insn->src1, &insn->src2) ||
               simplify_add_one_side(insn, &insn->src2, &insn->src1);
}

static int simplify_sub(struct instruction *insn)
{
        pseudo_t src1 = insn->src1;
        pseudo_t src2 = insn->src2;
        struct instruction *def;

        switch (DEF_OPCODE(def, src1)) {
        case OP_ADD:
                if (def->src1 == src2)          // (x + y) - x --> y
                        return replace_with_pseudo(insn, def->src2);
                if (def->src2 == src2)          // (x + y) - y --> x
                        return replace_with_pseudo(insn, def->src1);
                break;
        }

        switch (DEF_OPCODE(def, src2)) {
        case OP_ADD:
                if (src1 == def->src1)          // x - (x + z) --> -z
                        return replace_with_unop(insn, OP_NEG, def->src2);
                if (src1 == def->src2)          // x - (y + x) --> -y
                        return replace_with_unop(insn, OP_NEG, def->src1);
                break;
        case OP_NEG:                            // (x - -y) --> (x + y)
                insn->opcode = OP_ADD;
                return replace_pseudo(insn, &insn->src2, def->src);
        }

        return 0;
}

static int simplify_compare(struct instruction *insn)
{
        pseudo_t src1 = insn->src1;
        pseudo_t src2 = insn->src2;
        struct instruction *def = NULL;
        unsigned int osize;
        pseudo_t src;

        switch (DEF_OPCODE(def, src1)) {
        case OP_SEXT: case OP_ZEXT:
                osize = def->orig_type->bit_size;
                if ((src = is_same_op(src2, def->opcode, osize))) {
                        const struct opcode_table *op = &opcode_table[insn->opcode];
                        if ((def->opcode == OP_ZEXT) && (op->flags & OPF_SIGNED))
                                insn->opcode = op->sign;
                        insn->itype = def->orig_type;
                        replace_pseudo(insn, &insn->src1, def->src);
                        return replace_pseudo(insn, &insn->src2, src);
                }
                break;
        }
        return 0;
}

static int simplify_and_one_side(struct instruction *insn, pseudo_t *p1, pseudo_t *p2)
{
        struct instruction *def, *defr = NULL;
        pseudo_t src1 = *p1;

        switch (DEF_OPCODE(def, src1)) {
        case OP_NOT:
                if (def->src == *p2)
                        return replace_with_value(insn, 0);
                break;
        case OP_BINCMP ... OP_BINCMP_END:
                if (DEF_OPCODE(defr, *p2) == opcode_negate(def->opcode)) {
                        if (def->src1 == defr->src1 && def->src2 == defr->src2)
                                return replace_with_value(insn, 0);
                }
                break;
        case OP_OR:
                if (DEF_OPCODE(defr, *p2) == OP_OR) {
                        if (defr->src2 == def->src2 && can_move_to(def->src2, defr)) {
                                // ((x | z) & (y | z)) into ((x & y) | z)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src1 && can_move_to(def->src1, defr)) {
                                // ((z | x) & (z | y)) into ((x & y) | z)
                                swap_insn(insn, defr, def->src2, defr->src2, def->src1);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src2 && can_move_to(def->src1, defr)) {
                                // ((x | z) & (z | y)) into ((x & y) | z)
                                swap_insn(insn, defr, def->src1, defr->src2, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        case OP_SHL: case OP_LSR: case OP_ASR:
                if (DEF_OPCODE(defr, *p2) == def->opcode && defr->src2 == def->src2) {
                        if (can_move_to(def->src1, defr)) {
                                // SHIFT(x, s) & SHIFT(y, s) --> SHIFT((x & y), s)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        }
        return 0;
}

static int simplify_and(struct instruction *insn)
{
        return simplify_and_one_side(insn, &insn->src1, &insn->src2) ||
               simplify_and_one_side(insn, &insn->src2, &insn->src1);
}

static int simplify_ior_one_side(struct instruction *insn, pseudo_t *p1, pseudo_t *p2)
{
        struct instruction *def, *defr = NULL;
        pseudo_t src1 = *p1;

        switch (DEF_OPCODE(def, src1)) {
        case OP_AND:
                if (DEF_OPCODE(defr, *p2) == OP_AND) {
                        if (defr->src2 == def->src2 && can_move_to(def->src2, defr)) {
                                // ((x & z) | (y & z)) into ((x | y) & z)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src1 && can_move_to(def->src1, defr)) {
                                // ((z & x) | (z & y)) into ((x | y) & z)
                                swap_insn(insn, defr, def->src2, defr->src2, def->src1);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src2 && can_move_to(def->src1, defr)) {
                                // ((x & z) | (z & y)) into ((x | y) & z)
                                swap_insn(insn, defr, def->src1, defr->src2, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        case OP_NOT:
                if (def->src == *p2)
                        return replace_with_value(insn, bits_mask(insn->size));
                break;
        case OP_BINCMP ... OP_BINCMP_END:
                if (DEF_OPCODE(defr, *p2) == opcode_negate(def->opcode)) {
                        if (def->src1 == defr->src1 && def->src2 == defr->src2)
                                return replace_with_value(insn, 1);
                }
                break;
        case OP_SHL: case OP_LSR: case OP_ASR:
                if (DEF_OPCODE(defr, *p2) == def->opcode && defr->src2 == def->src2) {
                        if (can_move_to(def->src1, defr)) {
                                // SHIFT(x, s) | SHIFT(y, s) --> SHIFT((x | y), s)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        }
        return 0;
}

static int simplify_ior(struct instruction *insn)
{
        return simplify_ior_one_side(insn, &insn->src1, &insn->src2) ||
               simplify_ior_one_side(insn, &insn->src2, &insn->src1);
}

static int simplify_xor_one_side(struct instruction *insn, pseudo_t *p1, pseudo_t *p2)
{
        struct instruction *def, *defr = NULL;
        pseudo_t src1 = *p1;

        switch (DEF_OPCODE(def, src1)) {
        case OP_AND:
                if (DEF_OPCODE(defr, *p2) == OP_AND) {
                        if (defr->src2 == def->src2 && can_move_to(def->src2, defr)) {
                                // ((x & z) ^ (y & z)) into ((x ^ y) & z)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src1 && can_move_to(def->src1, defr)) {
                                // ((z & x) ^ (z & y)) into ((x ^ y) & z)
                                swap_insn(insn, defr, def->src2, defr->src2, def->src1);
                                return REPEAT_CSE;
                        }
                        if (defr->src1 == def->src2 && can_move_to(def->src1, defr)) {
                                // ((x & z) ^ (z & y)) into ((x ^ y) & z)
                                swap_insn(insn, defr, def->src1, defr->src2, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        case OP_NOT:
                if (def->src == *p2)
                        return replace_with_value(insn, bits_mask(insn->size));
                break;
        case OP_BINCMP ... OP_BINCMP_END:
                if (DEF_OPCODE(defr, *p2) == opcode_negate(def->opcode)) {
                        if (def->src1 == defr->src1 && def->src2 == defr->src2)
                                return replace_with_value(insn, 1);
                }
                break;
        case OP_SHL: case OP_LSR: case OP_ASR:
                if (DEF_OPCODE(defr, *p2) == def->opcode && defr->src2 == def->src2) {
                        if (can_move_to(def->src1, defr)) {
                                // SHIFT(x, s) ^ SHIFT(y, s) --> SHIFT((x ^ y), s)
                                swap_insn(insn, defr, def->src1, defr->src1, def->src2);
                                return REPEAT_CSE;
                        }
                }
                break;
        }
        return 0;
}

static int simplify_xor(struct instruction *insn)
{
        return simplify_xor_one_side(insn, &insn->src1, &insn->src2) ||
               simplify_xor_one_side(insn, &insn->src2, &insn->src1);
}

static int simplify_constant_unop(struct instruction *insn)
{
        long long val = insn->src1->value;
        long long res, mask;

        switch (insn->opcode) {
        case OP_NOT:
                res = ~val;
                break;
        case OP_NEG:
                res = -val;
                break;
        case OP_SEXT:
                mask = 1ULL << (insn->orig_type->bit_size-1);
                if (val & mask)
                        val |= ~(mask | (mask-1));
                /* fall through */
        case OP_ZEXT:
        case OP_TRUNC:
                res = val;
                break;
        default:
                return 0;
        }
        mask = 1ULL << (insn->size-1);
        res &= mask | (mask-1);
        
        return replace_with_value(insn, res);
}

static int simplify_unop(struct instruction *insn)
{
        struct instruction *def;
        pseudo_t src = insn->src;

        if (constant(src))
                return simplify_constant_unop(insn);

        switch (insn->opcode) {
        case OP_NOT:
                switch (DEF_OPCODE(def, src)) {
                case OP_ADD:
                        if (!constant(def->src2))
                                break;
                        insn->opcode = OP_SUB;  // ~(x + C) --> ~C - x
                        src = eval_unop(OP_NOT, insn->size, def->src2);
                        use_pseudo(insn, def->src1, &insn->src2);
                        return replace_pseudo(insn, &insn->src1, src);
                case OP_NEG:
                        insn->opcode = OP_SUB;  // ~(-x) --> x - 1
                        insn->src2 = value_pseudo(1);
                        return replace_pseudo(insn, &insn->src1, def->src);
                case OP_NOT:                    // ~(~x) --> x
                        return replace_with_pseudo(insn, def->src);
                case OP_SUB:
                        if (!constant(def->src1))
                                break;
                        insn->opcode = OP_ADD;  // ~(C - x) --> x + ~C
                        insn->src2 = eval_unop(OP_NOT, insn->size, def->src1);
                        return replace_pseudo(insn, &insn->src1, def->src2);
                case OP_XOR:
                        if (!constant(def->src2))
                                break;
                        insn->opcode = OP_XOR;  // ~(x ^ C) --> x ^ ~C
                        insn->src2 = eval_unop(OP_NOT, insn->size, def->src2);
                        return replace_pseudo(insn, &insn->src1, def->src1);
                }
                break;
        case OP_NEG:
                switch (DEF_OPCODE(def, src)) {
                case OP_ADD:
                        if (!constant(def->src2))
                                break;
                        insn->opcode = OP_SUB;  // -(x + C) --> (-C - x)
                        src = eval_unop(OP_NEG, insn->size, def->src2);
                        use_pseudo(insn, def->src1, &insn->src2);
                        return replace_pseudo(insn, &insn->src1, src);
                case OP_NEG:                    // -(-x) --> x
                        return replace_with_pseudo(insn, def->src);
                case OP_NOT:
                        insn->opcode = OP_ADD;  // -(~x) --> x + 1
                        insn->src2 = value_pseudo(1);
                        return replace_pseudo(insn, &insn->src1, def->src);
                case OP_SUB:
                        insn->opcode = OP_SUB;          // -(x - y) --> y - x
                        use_pseudo(insn, def->src1, &insn->src2);
                        return replace_pseudo(insn, &insn->src1, def->src2);
                }
                break;
        default:
                return 0;
        }
        return 0;
}

static int simplify_one_memop(struct instruction *insn, pseudo_t orig)
{
        pseudo_t addr = insn->src;
        pseudo_t new, off;

        if (addr->type == PSEUDO_REG) {
                struct instruction *def = addr->def;
                if (def->opcode == OP_SYMADDR && def->src) {
                        kill_use(&insn->src);
                        use_pseudo(insn, def->src, &insn->src);
                        return REPEAT_CSE;
                }
                if (def->opcode == OP_ADD) {
                        new = def->src1;
                        off = def->src2;
                        if (constant(off))
                                goto offset;
                        new = off;
                        off = def->src1;
                        if (constant(off))
                                goto offset;
                        return 0;
                }
        }
        return 0;

offset:
        /* Invalid code */
        if (new == orig || new == addr) {
                if (new == VOID)
                        return 0;
                /*
                 * If some BB have been removed it is possible that this
                 * memop is in fact part of a dead BB. In this case
                 * we must not warn since nothing is wrong.
                 * If not part of a dead BB this will be redone after
                 * the BBs have been cleaned up.
                 */
                if (repeat_phase & REPEAT_CFG_CLEANUP)
                        return 0;
                warning(insn->pos, "crazy programmer");
                replace_pseudo(insn, &insn->src, VOID);
                return 0;
        }
        insn->offset += off->value;
        replace_pseudo(insn, &insn->src, new);
        return REPEAT_CSE;
}

///
// simplify memops instructions
//
// :note: We walk the whole chain of adds/subs backwards.
//      That's not only more efficient, but it allows us to find loops.
static int simplify_memop(struct instruction *insn)
{
        int one, ret = 0;
        pseudo_t orig = insn->src;

        do {
                one = simplify_one_memop(insn, orig);
                ret |= one;
        } while (one);
        return ret;
}

static int simplify_cast(struct instruction *insn)
{
        unsigned long long mask;
        struct instruction *def;
        pseudo_t src = insn->src;
        pseudo_t val;
        int osize;
        int size;

        /* A cast of a constant? */
        if (constant(src))
                return simplify_constant_unop(insn);

        // can merge with the previous instruction?
        size = insn->size;
        def = src->def;
        switch (def_opcode(src)) {
        case OP_AND:
                val = def->src2;
                if (val->type != PSEUDO_VAL)
                        break;
                /* A cast of a AND might be a no-op.. */
                switch (insn->opcode) {
                case OP_TRUNC:
                        if (!one_use(src))
                                break;
                        def->opcode = OP_TRUNC;
                        def->orig_type = def->type;
                        def->type = insn->type;
                        def->size = size;

                        insn->opcode = OP_AND;
                        mask = val->value;
                        mask &= (1ULL << size) - 1;
                        insn->src2 = value_pseudo(mask);
                        return REPEAT_CSE;

                case OP_SEXT:
                        if (val->value & (1 << (def->size - 1)))
                                break;
                        // OK, sign bit is 0
                case OP_ZEXT:
                        if (!one_use(src))
                                break;
                        // transform:
                        //      and.n   %b <- %a, M
                        //      *ext.m  %c <- (n) %b
                        // into:
                        //      zext.m  %b <- %a
                        //      and.m   %c <- %b, M
                        // For ZEXT, the mask will always be small
                        // enough. For SEXT, it can only be done if
                        // the mask force the sign bit to 0.
                        def->opcode = OP_ZEXT;
                        def->orig_type = insn->orig_type;
                        def->type = insn->type;
                        def->size = insn->size;
                        insn->opcode = OP_AND;
                        insn->src2 = val;
                        return REPEAT_CSE;
                }
                break;
        case OP_FPCMP ... OP_BINCMP_END:
                switch (insn->opcode) {
                case OP_SEXT:
                        if (insn->size == 1)
                                break;
                        /* fall through */
                case OP_ZEXT:
                case OP_TRUNC:
                        // simplify:
                        //      setcc.n %t <- %a, %b
                        //      zext.m  %r <- (n) %t
                        // into:
                        //      setcc.m %r <- %a, %b
                        // and same for s/zext/trunc/
                        insn->opcode = def->opcode;
                        insn->itype = def->itype;
                        use_pseudo(insn, def->src2, &insn->src2);
                        return replace_pseudo(insn, &insn->src1, def->src1);
                }
                break;
        case OP_OR:
                switch (insn->opcode) {
                case OP_TRUNC:
                        mask = bits_mask(insn->size);
                        return simplify_mask_or(insn, mask, def);
                }
                break;
        case OP_LSR:
        case OP_SHL:
                if (insn->opcode != OP_TRUNC)
                        break;
                mask = bits_mask(insn->size);
                return simplify_mask_shift(def, mask);
        case OP_TRUNC:
                switch (insn->opcode) {
                case OP_TRUNC:
                        insn->orig_type = def->orig_type;
                        return replace_pseudo(insn, &insn->src1, def->src);
                case OP_ZEXT:
                        if (size != def->orig_type->bit_size)
                                break;
                        insn->opcode = OP_AND;
                        insn->src2 = value_pseudo((1ULL << def->size) - 1);
                        return replace_pseudo(insn, &insn->src1, def->src);
                }
                break;
        case OP_ZEXT:
                switch (insn->opcode) {
                case OP_SEXT:
                        insn->opcode = OP_ZEXT;
                        /* fall through */
                case OP_ZEXT:
                        insn->orig_type = def->orig_type;
                        return replace_pseudo(insn, &insn->src, def->src);
                }
                /* fall through */
        case OP_SEXT:
                switch (insn->opcode) {
                case OP_TRUNC:
                        osize = def->orig_type->bit_size;
                        if (size == osize)
                                return replace_with_pseudo(insn, def->src);
                        if (size > osize)
                                insn->opcode = def->opcode;
                        insn->orig_type = def->orig_type;
                        return replace_pseudo(insn, &insn->src, def->src);
                }
                switch (insn->opcode) {
                case OP_SEXT:
                        insn->orig_type = def->orig_type;
                        return replace_pseudo(insn, &insn->src, def->src);
                }
                break;
        }

        return 0;
}

static int simplify_select(struct instruction *insn)
{
        pseudo_t cond, src1, src2;
        struct instruction *def;

        cond = insn->src1;
        src1 = insn->src2;
        src2 = insn->src3;

        if (constant(cond))
                return replace_with_pseudo(insn, cond->value ? src1 : src2);
        if (src1 == src2)
                return replace_with_pseudo(insn, src1);

        if (constant(src1) && constant(src2)) {
                long long val1 = src1->value;
                long long val2 = src2->value;

                /* The pair 0/1 is special - replace with SETNE/SETEQ */
                if ((val1 | val2) == 1) {
                        int opcode = OP_SET_EQ;
                        if (val1) {
                                src1 = src2;
                                opcode = OP_SET_NE;
                        }
                        insn->opcode = opcode;
                        /* insn->src1 is already cond */
                        insn->src2 = src1; /* Zero */
                        return REPEAT_CSE;
                }
        }
        if (cond == src2 && is_zero(src1))                      // SEL(x, 0, x) --> 0
                return replace_with_pseudo(insn, src1);
        if (cond == src1 && is_zero(src2))                      // SEL(x, x, 0) --> x
                return replace_with_pseudo(insn, cond);

        switch (DEF_OPCODE(def, cond)) {
        case OP_SET_EQ:
                if (src1 == def->src1 && src2 == def->src2)
                        return replace_with_pseudo(insn, src2); // SEL(x==y,x,y) --> y
                if (src2 == def->src1 && src1 == def->src2)
                        return replace_with_pseudo(insn, src2); // SEL(y==x,x,y) --> y
                break;
        case OP_SET_NE:
                if (src1 == def->src1 && src2 == def->src2)
                        return replace_with_pseudo(insn, src1); // SEL(x!=y,x,y) --> x
                if (src2 == def->src1 && src1 == def->src2)
                        return replace_with_pseudo(insn, src1); // SEL(y!=x,x,y) --> x
                break;
        case OP_SEL:
                if (constant(def->src2) && constant(def->src3)) {
                        // Is the def of the conditional another select?
                        // And if that one results in a "zero or not", use the
                        // original conditional instead.
                        //      SEL(SEL(x, C, 0), y, z) --> SEL(x, y, z)
                        //      SEL(SEL(x, C, 0), C, 0) --> SEL(x, C, 0) == cond
                        //      SEL(SEL(x, 0, C), y, z) --> SEL(x, z, y)
                        //      SEL(SEL(x, C1, C2), y, z) --> y
                        if (!def->src3->value) {
                                if ((src1 == def->src2) && (src2 == def->src3))
                                        return replace_with_pseudo(insn, cond);
                                return replace_pseudo(insn, &insn->cond, def->cond);
                        }
                        if (!def->src2->value) {
                                switch_pseudo(insn, &insn->src2, insn, &insn->src3);
                                return replace_pseudo(insn, &insn->cond, def->cond);
                        }
                        // both values must be non-zero
                        return replace_with_pseudo(insn, src1);
                }
        case OP_AND:
                if (is_pow2(def->src2) && is_pow2(src1) && is_zero(src2) && insn->size == def->size && one_use(cond)) {
                        unsigned s1 = log2_exact(def->src2->value);
                        unsigned s2 = log2_exact(insn->src2->value);
                        unsigned shift;

                        if (s1 == s2)
                                return replace_with_pseudo(insn, cond);

                        // SEL(x & A, B, 0) --> SHIFT(x & A, S)
                        insn->opcode = (s1 < s2) ? OP_SHL : OP_LSR;
                        shift = (s1 < s2) ? (s2 - s1) : (s1 - s2);
                        insn->src2 = value_pseudo(shift);
                        return REPEAT_CSE;
                }
                break;
        }

        switch (DEF_OPCODE(def, src1)) {
        case OP_ADD: case OP_OR: case OP_XOR:
                if ((def->src1 == src2) && can_move_to(cond, def)) {
                        // SEL(x, OP(y,z), y) --> OP(SEL(x, z, 0), y)
                        swap_select(insn, def, cond, def->src2, value_pseudo(0), src2);
                        return REPEAT_CSE;
                }
                if ((def->src2 == src2) && can_move_to(cond, def)) {
                        // SEL(x, OP(z,y), y) --> OP(SEL(x, z, 0), y)
                        swap_select(insn, def, cond, def->src1, value_pseudo(0), src2);
                        return REPEAT_CSE;
                }
                break;
        }

        switch (DEF_OPCODE(def, src2)) {
        case OP_ADD: case OP_OR: case OP_XOR:
                if ((def->src1 == src1) && can_move_to(cond, def)) {
                        // SEL(x, y, OP(y,z)) --> OP(SEL(x, 0, z), y)
                        swap_select(insn, def, cond, value_pseudo(0), def->src2, src1);
                        return REPEAT_CSE;
                }
                if ((def->src2 == src1) && can_move_to(cond, def)) {
                        // SEL(x, y, OP(z,y)) --> OP(SEL(x, 0, z), y)
                        swap_select(insn, def, cond, value_pseudo(0), def->src1, src1);
                        return REPEAT_CSE;
                }
                break;
        }
        return 0;
}

static int is_in_range(pseudo_t src, long long low, long long high)
{
        long long value;

        switch (src->type) {
        case PSEUDO_VAL:
                value = src->value;
                return value >= low && value <= high;
        default:
                return 0;
        }
}

static int simplify_range(struct instruction *insn)
{
        pseudo_t src1, src2, src3;

        src1 = insn->src1;
        src2 = insn->src2;
        src3 = insn->src3;
        if (src2->type != PSEUDO_VAL || src3->type != PSEUDO_VAL)
                return 0;
        if (is_in_range(src1, src2->value, src3->value)) {
                kill_instruction(insn);
                return REPEAT_CSE;
        }
        return 0;
}

///
// simplify SET_NE/EQ $0 + BR
static int simplify_cond_branch(struct instruction *br, struct instruction *def, pseudo_t newcond)
{
        replace_pseudo(br, &br->cond, newcond);
        if (def->opcode == OP_SET_EQ) {
                struct basic_block *tmp = br->bb_true;
                br->bb_true = br->bb_false;
                br->bb_false = tmp;
        }
        return REPEAT_CSE;
}

static int simplify_branch(struct instruction *insn)
{
        pseudo_t cond = insn->cond;

        /* Constant conditional */
        if (constant(cond)) {
                insert_branch(insn->bb, insn, cond->value ? insn->bb_true : insn->bb_false);
                return REPEAT_CSE;
        }

        /* Same target? */
        if (insn->bb_true == insn->bb_false) {
                struct basic_block *bb = insn->bb;
                struct basic_block *target = insn->bb_false;
                remove_bb_from_list(&target->parents, bb, 1);
                remove_bb_from_list(&bb->children, target, 1);
                insn->bb_false = NULL;
                kill_use(&insn->cond);
                insn->cond = NULL;
                insn->opcode = OP_BR;
                return REPEAT_CSE|REPEAT_CFG_CLEANUP;
        }

        /* Conditional on a SETNE $0 or SETEQ $0 */
        if (cond->type == PSEUDO_REG) {
                struct instruction *def = cond->def;

                if (def->opcode == OP_SET_NE || def->opcode == OP_SET_EQ) {
                        if (constant(def->src1) && !def->src1->value)
                                return simplify_cond_branch(insn, def, def->src2);
                        if (constant(def->src2) && !def->src2->value)
                                return simplify_cond_branch(insn, def, def->src1);
                }
                if (def->opcode == OP_SEL) {
                        if (constant(def->src2) && constant(def->src3)) {
                                long long val1 = def->src2->value;
                                long long val2 = def->src3->value;
                                if (!val1 && !val2) {
                                        insert_branch(insn->bb, insn, insn->bb_false);
                                        return REPEAT_CSE;
                                }
                                if (val1 && val2) {
                                        insert_branch(insn->bb, insn, insn->bb_true);
                                        return REPEAT_CSE;
                                }
                                if (val2) {
                                        struct basic_block *tmp = insn->bb_true;
                                        insn->bb_true = insn->bb_false;
                                        insn->bb_false = tmp;
                                }
                                return replace_pseudo(insn, &insn->cond, def->src1);
                        }
                }
                if (def->opcode == OP_SEXT || def->opcode == OP_ZEXT)
                        return replace_pseudo(insn, &insn->cond, def->src);
        }
        return 0;
}

static int simplify_switch(struct instruction *insn)
{
        pseudo_t cond = insn->cond;
        long long val;
        struct multijmp *jmp;

        if (!constant(cond))
                return 0;
        val = insn->cond->value;

        FOR_EACH_PTR(insn->multijmp_list, jmp) {
                /* Default case */
                if (jmp->begin > jmp->end)
                        goto found;
                if (val >= jmp->begin && val <= jmp->end)
                        goto found;
        } END_FOR_EACH_PTR(jmp);
        warning(insn->pos, "Impossible case statement");
        return 0;

found:
        insert_branch(insn->bb, insn, jmp->target);
        return REPEAT_CSE;
}

static struct basic_block *is_label(pseudo_t pseudo)
{
        struct instruction *def;

        if (DEF_OPCODE(def, pseudo) != OP_LABEL)
                return NULL;
        return def->bb_true;
}

static int simplify_cgoto(struct instruction *insn)
{
        struct basic_block *target, *bb = insn->bb;
        struct basic_block *bbt, *bbf;
        struct instruction *def;
        struct multijmp *jmp;

        switch (DEF_OPCODE(def, insn->src)) {
        case OP_SEL:    // CGOTO(SEL(x, L1, L2)) --> CBR x, L1, L2
                if ((bbt = is_label(def->src2)) && (bbf = is_label(def->src3))) {
                        insn->opcode = OP_CBR;
                        insn->bb_true = bbt;
                        insn->bb_false = bbf;
                        return replace_pseudo(insn, &insn->src1, def->cond);
                }
                break;
        case OP_LABEL:
                target = def->bb_true;
                if (!target->ep)
                        return 0;
                FOR_EACH_PTR(insn->multijmp_list, jmp) {
                        if (jmp->target == target)
                                continue;
                        remove_bb_from_list(&jmp->target->parents, bb, 1);
                        remove_bb_from_list(&bb->children, jmp->target, 1);
                        MARK_CURRENT_DELETED(jmp);
                } END_FOR_EACH_PTR(jmp);
                kill_use(&insn->src);
                insn->opcode = OP_BR;
                insn->bb_true = target;
                return REPEAT_CSE|REPEAT_CFG_CLEANUP;
        }
        return 0;
}

static int simplify_setval(struct instruction *insn)
{
        struct expression *val = insn->val;

        switch (val->type) {
        case EXPR_LABEL:
                insn->opcode = OP_LABEL;
                insn->bb_true = val->symbol->bb_target;
                return REPEAT_CSE;
        default:
                break;
        }
        return 0;
}

int simplify_instruction(struct instruction *insn)
{
        unsigned flags;
        int changed = 0;

        flags = opcode_table[insn->opcode].flags;
        if (flags & OPF_TARGET) {
                if (!has_users(insn->target))
                        return kill_instruction(insn);
        }
        if (flags & OPF_COMMU)
                canonicalize_commutative(insn) ;
        if (flags & OPF_COMPARE)
                canonicalize_compare(insn) ;
        if (flags & OPF_BINOP) {
                if ((changed = simplify_binop(insn)))
                        return changed;
        }
        if (flags & OPF_ASSOC) {
                if ((changed = simplify_associative_binop(insn)))
                        return changed;
        }
        if (flags & OPF_UNOP) {
                if ((changed = simplify_unop(insn)))
                        return changed;
        }

        switch (insn->opcode) {
        case OP_ADD: return simplify_add(insn);
        case OP_SUB: return simplify_sub(insn);
        case OP_AND: return simplify_and(insn);
        case OP_OR:  return simplify_ior(insn);
        case OP_XOR: return simplify_xor(insn);
        case OP_MUL:
        case OP_SHL:
        case OP_LSR:
        case OP_ASR:
        case OP_NOT:
        case OP_NEG:
        case OP_DIVU:
        case OP_DIVS:
        case OP_MODU:
        case OP_MODS:
                break;
        case OP_BINCMP ... OP_BINCMP_END:
                return simplify_compare(insn);
        case OP_LOAD:
        case OP_STORE:
                return simplify_memop(insn);
        case OP_SYMADDR:
                return replace_with_pseudo(insn, insn->src);
        case OP_SEXT: case OP_ZEXT:
        case OP_TRUNC:
                return simplify_cast(insn);
        case OP_FNEG:
        case OP_FCVTU: case OP_FCVTS:
        case OP_UCVTF: case OP_SCVTF:
        case OP_FCVTF:
        case OP_PTRCAST:
                break;
        case OP_UTPTR:
        case OP_PTRTU:
                return replace_with_pseudo(insn, insn->src);
        case OP_SLICE:
                break;
        case OP_SETVAL:
                return simplify_setval(insn);
        case OP_LABEL:
        case OP_SETFVAL:
                break;
        case OP_PHI:
                return clean_up_phi(insn);
        case OP_PHISOURCE:
                break;
        case OP_SEL:
                return simplify_select(insn);
        case OP_CBR:
                return simplify_branch(insn);
        case OP_SWITCH:
                return simplify_switch(insn);
        case OP_COMPUTEDGOTO:
                return simplify_cgoto(insn);
        case OP_RANGE:
                return simplify_range(insn);
        case OP_FADD:
        case OP_FSUB:
        case OP_FMUL:
        case OP_FDIV:
                break;
        }
        return 0;
}