path: root/tcg/optimize.c

/*
 * Optimizations for Tiny Code Generator for QEMU
 *
 * Copyright (c) 2010 Samsung Electronics.
 * Contributed by Kirill Batuzov <batuzovk@ispras.ru>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu/osdep.h"
#include "qemu-common.h"
#include "exec/cpu-common.h"
#include "tcg-op.h"

#define CASE_OP_32_64(x)                        \
        glue(glue(case INDEX_op_, x), _i32):    \
        glue(glue(case INDEX_op_, x), _i64)

#define CASE_OP_32_64_VEC(x)                    \
        glue(glue(case INDEX_op_, x), _i32):    \
        glue(glue(case INDEX_op_, x), _i64):    \
        glue(glue(case INDEX_op_, x), _vec)

struct tcg_temp_info {
    bool is_const;
    TCGTemp *prev_copy;
    TCGTemp *next_copy;
    tcg_target_ulong val;
    tcg_target_ulong mask;
};

static inline struct tcg_temp_info *ts_info(TCGTemp *ts)
{
    return ts->state_ptr;
}

static inline struct tcg_temp_info *arg_info(TCGArg arg)
{
    return ts_info(arg_temp(arg));
}

static inline bool ts_is_const(TCGTemp *ts)
{
    return ts_info(ts)->is_const;
}

static inline bool arg_is_const(TCGArg arg)
{
    return ts_is_const(arg_temp(arg));
}

static inline bool ts_is_copy(TCGTemp *ts)
{
    return ts_info(ts)->next_copy != ts;
}

/* Reset TEMP's state, possibly removing the temp for the list of copies.  */
static void reset_ts(TCGTemp *ts)
{
    struct tcg_temp_info *ti = ts_info(ts);
    struct tcg_temp_info *pi = ts_info(ti->prev_copy);
    struct tcg_temp_info *ni = ts_info(ti->next_copy);

    ni->prev_copy = ti->prev_copy;
    pi->next_copy = ti->next_copy;
    ti->next_copy = ts;
    ti->prev_copy = ts;
    ti->is_const = false;
    ti->mask = -1;
}

static void reset_temp(TCGArg arg)
{
    reset_ts(arg_temp(arg));
}

/* Initialize and activate a temporary.  */
static void init_ts_info(struct tcg_temp_info *infos,
                         TCGTempSet *temps_used, TCGTemp *ts)
{
    size_t idx = temp_idx(ts);
    if (!test_bit(idx, temps_used->l)) {
        struct tcg_temp_info *ti = &infos[idx];

        ts->state_ptr = ti;
        ti->next_copy = ts;
        ti->prev_copy = ts;
        ti->is_const = false;
        ti->mask = -1;
        set_bit(idx, temps_used->l);
    }
}

static void init_arg_info(struct tcg_temp_info *infos,
                          TCGTempSet *temps_used, TCGArg arg)
{
    init_ts_info(infos, temps_used, arg_temp(arg));
}

static TCGTemp *find_better_copy(TCGContext *s, TCGTemp *ts)
{
    TCGTemp *i;

    /* If this is already a global, we can't do better. */
    if (ts->temp_global) {
        return ts;
    }

    /* Search for a global first. */
    for (i = ts_info(ts)->next_copy; i != ts; i = ts_info(i)->next_copy) {
        if (i->temp_global) {
            return i;
        }
    }

    /* If it is a temp, search for a temp local. */
    if (!ts->temp_local) {
        for (i = ts_info(ts)->next_copy; i != ts; i = ts_info(i)->next_copy) {
            if (ts->temp_local) {
                return i;
            }
        }
    }

    /* Failure to find a better representation, return the same temp. */
    return ts;
}

static bool ts_are_copies(TCGTemp *ts1, TCGTemp *ts2)
{
    TCGTemp *i;

    if (ts1 == ts2) {
        return true;
    }

    if (!ts_is_copy(ts1) || !ts_is_copy(ts2)) {
        return false;
    }

    for (i = ts_info(ts1)->next_copy; i != ts1; i = ts_info(i)->next_copy) {
        if (i == ts2) {
            return true;
        }
    }

    return false;
}

static bool args_are_copies(TCGArg arg1, TCGArg arg2)
{
    return ts_are_copies(arg_temp(arg1), arg_temp(arg2));
}

static void tcg_opt_gen_movi(TCGContext *s, TCGOp *op, TCGArg dst, TCGArg val)
{
    const TCGOpDef *def;
    TCGOpcode new_op;
    tcg_target_ulong mask;
    struct tcg_temp_info *di = arg_info(dst);

    def = &tcg_op_defs[op->opc];
    if (def->flags & TCG_OPF_VECTOR) {
        new_op = INDEX_op_dupi_vec;
    } else if (def->flags & TCG_OPF_64BIT) {
        new_op = INDEX_op_movi_i64;
    } else {
        new_op = INDEX_op_movi_i32;
    }
    op->opc = new_op;
    /* TCGOP_VECL and TCGOP_VECE remain unchanged.  */
    op->args[0] = dst;
    op->args[1] = val;

    reset_temp(dst);
    di->is_const = true;
    di->val = val;
    mask = val;
    if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_movi_i32) {
        /* High bits of the destination are now garbage.  */
        mask |= ~0xffffffffull;
    }
    di->mask = mask;
}

static void tcg_opt_gen_mov(TCGContext *s, TCGOp *op, TCGArg dst, TCGArg src)
{
    TCGTemp *dst_ts = arg_temp(dst);
    TCGTemp *src_ts = arg_temp(src);
    const TCGOpDef *def;
    struct tcg_temp_info *di;
    struct tcg_temp_info *si;
    tcg_target_ulong mask;
    TCGOpcode new_op;

    if (ts_are_copies(dst_ts, src_ts)) {
        tcg_op_remove(s, op);
        return;
    }

    reset_ts(dst_ts);
    di = ts_info(dst_ts);
    si = ts_info(src_ts);
    def = &tcg_op_defs[op->opc];
    if (def->flags & TCG_OPF_VECTOR) {
        new_op = INDEX_op_mov_vec;
    } else if (def->flags & TCG_OPF_64BIT) {
        new_op = INDEX_op_mov_i64;
    } else {
        new_op = INDEX_op_mov_i32;
    }
    op->opc = new_op;
    /* TCGOP_VECL and TCGOP_VECE remain unchanged.  */
    op->args[0] = dst;
    op->args[1] = src;

    mask = si->mask;
    if (TCG_TARGET_REG_BITS > 32 && new_op == INDEX_op_mov_i32) {
        /* High bits of the destination are now garbage.  */
        mask |= ~0xffffffffull;
    }
    di->mask = mask;

    if (src_ts->type == dst_ts->type) {
        struct tcg_temp_info *ni = ts_info(si->next_copy);

        di->next_copy = si->next_copy;
        di->prev_copy = src_ts;
        ni->prev_copy = dst_ts;
        si->next_copy = dst_ts;
        di->is_const = si->is_const;
        di->val = si->val;
    }
}

static TCGArg do_constant_folding_2(TCGOpcode op, TCGArg x, TCGArg y)
{
    uint64_t l64, h64;

    switch (op) {
    CASE_OP_32_64(add):
        return x + y;

    CASE_OP_32_64(sub):
        return x - y;

    CASE_OP_32_64(mul):
        return x * y;

    CASE_OP_32_64(and):
        return x & y;

    CASE_OP_32_64(or):
        return x | y;

    CASE_OP_32_64(xor):
        return x ^ y;

    case INDEX_op_shl_i32:
        return (uint32_t)x << (y & 31);

    case INDEX_op_shl_i64:
        return (uint64_t)x << (y & 63);

    case INDEX_op_shr_i32:
        return (uint32_t)x >> (y & 31);

    case INDEX_op_shr_i64:
        return (uint64_t)x >> (y & 63);

    case INDEX_op_sar_i32:
        return (int32_t)x >> (y & 31);

    case INDEX_op_sar_i64:
        return (int64_t)x >> (y & 63);

    case INDEX_op_rotr_i32:
        return ror32(x, y & 31);

    case INDEX_op_rotr_i64:
        return ror64(x, y & 63);

    case INDEX_op_rotl_i32:
        return rol32(x, y & 31);

    case INDEX_op_rotl_i64:
        return rol64(x, y & 63);

    CASE_OP_32_64(not):
        return ~x;

    CASE_OP_32_64(neg):
        return -x;

    CASE_OP_32_64(andc):
        return x & ~y;

    CASE_OP_32_64(orc):
        return x | ~y;

    CASE_OP_32_64(eqv):
        return ~(x ^ y);

    CASE_OP_32_64(nand):
        return ~(x & y);

    CASE_OP_32_64(nor):
        return ~(x | y);

    case INDEX_op_clz_i32:
        return (uint32_t)x ? clz32(x) : y;

    case INDEX_op_clz_i64:
        return x ? clz64(x) : y;

    case INDEX_op_ctz_i32:
        return (uint32_t)x ? ctz32(x) : y;

    case INDEX_op_ctz_i64:
        return x ? ctz64(x) : y;

    case INDEX_op_ctpop_i32:
        return ctpop32(x);

    case INDEX_op_ctpop_i64:
        return ctpop64(x);

    CASE_OP_32_64(ext8s):
        return (int8_t)x;

    CASE_OP_32_64(ext16s):
        return (int16_t)x;

    CASE_OP_32_64(ext8u):
        return (uint8_t)x;

    CASE_OP_32_64(ext16u):
        return (uint16_t)x;

    case INDEX_op_ext_i32_i64:
    case INDEX_op_ext32s_i64:
        return (int32_t)x;

    case INDEX_op_extu_i32_i64:
    case INDEX_op_extrl_i64_i32:
    case INDEX_op_ext32u_i64:
        return (uint32_t)x;

    case INDEX_op_extrh_i64_i32:
        return (uint64_t)x >> 32;

    case INDEX_op_muluh_i32:
        return ((uint64_t)(uint32_t)x * (uint32_t)y) >> 32;
    case INDEX_op_mulsh_i32:
        return ((int64_t)(int32_t)x * (int32_t)y) >> 32;

    case INDEX_op_muluh_i64:
        mulu64(&l64, &h64, x, y);
        return h64;
    case INDEX_op_mulsh_i64:
        muls64(&l64, &h64, x, y);
        return h64;

    case INDEX_op_div_i32:
        /* Avoid crashing on divide by zero, otherwise undefined.  */
        return (int32_t)x / ((int32_t)y ? : 1);
    case INDEX_op_divu_i32:
        return (uint32_t)x / ((uint32_t)y ? : 1);
    case INDEX_op_div_i64:
        return (int64_t)x / ((int64_t)y ? : 1);
    case INDEX_op_divu_i64:
        return (uint64_t)x / ((uint64_t)y ? : 1);

    case INDEX_op_rem_i32:
        return (int32_t)x % ((int32_t)y ? : 1);
    case INDEX_op_remu_i32:
        return (uint32_t)x % ((uint32_t)y ? : 1);
    case INDEX_op_rem_i64:
        return (int64_t)x % ((int64_t)y ? : 1);
    case INDEX_op_remu_i64:
        return (uint64_t)x % ((uint64_t)y ? : 1);

    default:
        fprintf(stderr,
                "Unrecognized operation %d in do_constant_folding.\n", op);
        tcg_abort();
    }
}

static TCGArg do_constant_folding(TCGOpcode op, TCGArg x, TCGArg y)
{
    const TCGOpDef *def = &tcg_op_defs[op];
    TCGArg res = do_constant_folding_2(op, x, y);
    if (!(def->flags & TCG_OPF_64BIT)) {
        res = (int32_t)res;
    }
    return res;
}

static bool do_constant_folding_cond_32(uint32_t x, uint32_t y, TCGCond c)
{
    switch (c) {
    case TCG_COND_EQ:
        return x == y;
    case TCG_COND_NE:
        return x != y;
    case TCG_COND_LT:
        return (int32_t)x < (int32_t)y;
    case TCG_COND_GE:
        return (int32_t)x >= (int32_t)y;
    case TCG_COND_LE:
        return (int32_t)x <= (int32_t)y;
    case TCG_COND_GT:
        return (int32_t)x > (int32_t)y;
    case TCG_COND_LTU:
        return x < y;
    case TCG_COND_GEU:
        return x >= y;
    case TCG_COND_LEU:
        return x <= y;
    case TCG_COND_GTU:
        return x > y;
    default:
        tcg_abort();
    }
}

static bool do_constant_folding_cond_64(uint64_t x, uint64_t y, TCGCond c)
{
    switch (c) {
    case TCG_COND_EQ:
        return x == y;
    case TCG_COND_NE:
        return x != y;
    case TCG_COND_LT:
        return (int64_t)x < (int64_t)y;
    case TCG_COND_GE:
        return (int64_t)x >= (int64_t)y;
    case TCG_COND_LE:
        return (int64_t)x <= (int64_t)y;
    case TCG_COND_GT:
        return (int64_t)x > (int64_t)y;
    case TCG_COND_LTU:
        return x < y;
    case TCG_COND_GEU:
        return x >= y;
    case TCG_COND_LEU:
        return x <= y;
    case TCG_COND_GTU:
        return x > y;
    default:
        tcg_abort();
    }
}

static bool do_constant_folding_cond_eq(TCGCond c)
{
    switch (c) {
    case TCG_COND_GT:
    case TCG_COND_LTU:
    case TCG_COND_LT:
    case TCG_COND_GTU:
    case TCG_COND_NE:
        return 0;
    case TCG_COND_GE:
    case TCG_COND_GEU:
    case TCG_COND_LE:
    case TCG_COND_LEU:
    case TCG_COND_EQ:
        return 1;
    default:
        tcg_abort();
    }
}

/* Return 2 if the condition can't be simplified, and the result
   of the condition (0 or 1) if it can */
static TCGArg do_constant_folding_cond(TCGOpcode op, TCGArg x,
                                       TCGArg y, TCGCond c)
{
    tcg_target_ulong xv = arg_info(x)->val;
    tcg_target_ulong yv = arg_info(y)->val;
    if (arg_is_const(x) && arg_is_const(y)) {
        const TCGOpDef *def = &tcg_op_defs[op];
        tcg_debug_assert(!(def->flags & TCG_OPF_VECTOR));
        if (def->flags & TCG_OPF_64BIT) {
            return do_constant_folding_cond_64(xv, yv, c);
        } else {
            return do_constant_folding_cond_32(xv, yv, c);
        }
    } else if (args_are_copies(x, y)) {
        return do_constant_folding_cond_eq(c);
    } else if (arg_is_const(y) && yv == 0) {
        switch (c) {
        case TCG_COND_LTU:
            return 0;
        case TCG_COND_GEU:
            return 1;
        default:
            return 2;
        }
    }
    return 2;
}

/* Return 2 if the condition can't be simplified, and the result
   of the condition (0 or 1) if it can */
static TCGArg do_constant_folding_cond2(TCGArg *p1, TCGArg *p2, TCGCond c)
{
    TCGArg al = p1[0], ah = p1[1];
    TCGArg bl = p2[0], bh = p2[1];

    if (arg_is_const(bl) && arg_is_const(bh)) {
        tcg_target_ulong blv = arg_info(bl)->val;
        tcg_target_ulong bhv = arg_info(bh)->val;
        uint64_t b = deposit64(blv, 32, 32, bhv);

        if (arg_is_const(al) && arg_is_const(ah)) {
            tcg_target_ulong alv = arg_info(al)->val;
            tcg_target_ulong ahv = arg_info(ah)->val;
            uint64_t a = deposit64(alv, 32, 32, ahv);
            return do_constant_folding_cond_64(a, b, c);
        }
        if (b == 0) {
            switch (c) {
            case TCG_COND_LTU:
                return 0;
            case TCG_COND_GEU:
                return 1;
            default:
                break;
            }
        }
    }
    if (args_are_copies(al, bl) && args_are_copies(ah, bh)) {
        return do_constant_folding_cond_eq(c);
    }
    return 2;
}

static bool swap_commutative(TCGArg dest, TCGArg *p1, TCGArg *p2)
{
    TCGArg a1 = *p1, a2 = *p2;
    int sum = 0;
    sum += arg_is_const(a1);
    sum -= arg_is_const(a2);

    /* Prefer the constant in second argument, and then the form
       op a, a, b, which is better handled on non-RISC hosts. */
    if (sum > 0 || (sum == 0 && dest == a2)) {
        *p1 = a2;
        *p2 = a1;
        return true;
    }
    return false;
}

static bool swap_commutative2(TCGArg *p1, TCGArg *p2)
{
    int sum = 0;
    sum += arg_is_const(p1[0]);
    sum += arg_is_const(p1[1]);
    sum -= arg_is_const(p2[0]);
    sum -= arg_is_const(p2[1]);
    if (sum > 0) {
        TCGArg t;
        t = p1[0], p1[0] = p2[0], p2[0] = t;
        t = p1[1], p1[1] = p2[1], p2[1] = t;
        return true;
    }
    return false;
}

/* Propagate constants and copies, fold constant expressions. */
void tcg_optimize(TCGContext *s)
{
    int nb_temps, nb_globals;
    TCGOp *op, *op_next, *prev_mb = NULL;
    struct tcg_temp_info *infos;
    TCGTempSet temps_used;

    /* Array VALS has an element for each temp.
       If this temp holds a constant then its value is kept in VALS' element.
       If this temp is a copy of other ones then the other copies are
       available through the doubly linked circular list. */

    nb_temps = s->nb_temps;
    nb_globals = s->nb_globals;
    bitmap_zero(temps_used.l, nb_temps);
    infos = tcg_malloc(sizeof(struct tcg_temp_info) * nb_temps);

    QTAILQ_FOREACH_SAFE(op, &s->ops, link, op_next) {
        tcg_target_ulong mask, partmask, affected;
        int nb_oargs, nb_iargs, i;
        TCGArg tmp;
        TCGOpcode opc = op->opc;
        const TCGOpDef *def = &tcg_op_defs[opc];

        /* Count the arguments, and initialize the temps that are
           going to be used */
        if (opc == INDEX_op_call) {
            nb_oargs = TCGOP_CALLO(op);
            nb_iargs = TCGOP_CALLI(op);
            for (i = 0; i < nb_oargs + nb_iargs; i++) {
                TCGTemp *ts = arg_temp(op->args[i]);
                if (ts) {
                    init_ts_info(infos, &temps_used, ts);
                }
            }
        } else {
            nb_oargs = def->nb_oargs;
            nb_iargs = def->nb_iargs;
            for (i = 0; i < nb_oargs + nb_iargs; i++) {
                init_arg_info(infos, &temps_used, op->args[i]);
            }
        }

        /* Do copy propagation */
        for (i = nb_oargs; i < nb_oargs + nb_iargs; i++) {
            TCGTemp *ts = arg_temp(op->args[i]);
            if (ts && ts_is_copy(ts)) {
                op->args[i] = temp_arg(find_better_copy(s, ts));
            }
        }

        /* For commutative operations make constant second argument */
        switch (opc) {
        CASE_OP_32_64_VEC(add):
        CASE_OP_32_64_VEC(mul):
        CASE_OP_32_64_VEC(and):
        CASE_OP_32_64_VEC(or):
        CASE_OP_32_64_VEC(xor):
        CASE_OP_32_64(eqv):
        CASE_OP_32_64(nand):
        CASE_OP_32_64(nor):
        CASE_OP_32_64(muluh):
        CASE_OP_32_64(mulsh):
            swap_commutative(op->args[0], &op->args[1], &op->args[2]);
            break;
        CASE_OP_32_64(brcond):
            if (swap_commutative(-1, &op->args[0], &op->args[1])) {
                op->args[2] = tcg_swap_cond(op->args[2]);
            }
            break;
        CASE_OP_32_64(setcond):
            if (swap_commutative(op->args[0], &op->args[1], &op->args[2])) {
                op->args[3] = tcg_swap_cond(op->args[3]);
            }
            break;
        CASE_OP_32_64(movcond):
            if (swap_commutative(-1, &op->args[1], &op->args[2])) {
                op->args[5] = tcg_swap_cond(op->args[5]);
            }
            /* For movcond, we canonicalize the "false" input reg to match
               the destination reg so that the tcg backend can implement
               a "move if true" operation.  */
            if (swap_commutative(op->args[0], &op->args[4], &op->args[3])) {
                op->args[5] = tcg_invert_cond(op->args[5]);
            }
            break;
        CASE_OP_32_64(add2):
            swap_commutative(op->args[0], &op->args[2], &op->args[4]);
            swap_commutative(op->args[1], &op->args[3], &op->args[5]);
            break;
        CASE_OP_32_64(mulu2):
        CASE_OP_32_64(muls2):
            swap_commutative(op->args[0], &op->args[2], &op->args[3]);
            break;
        case INDEX_op_brcond2_i32:
            if (swap_commutative2(&op->args[0], &op->args[2])) {
                op->args[4] = tcg_swap_cond(op->args[4]);
            }
            break;
        case INDEX_op_setcond2_i32:
            if (swap_commutative2(&op->args[1], &op->args[3])) {
                op->args[5] = tcg_swap_cond(op->args[5]);
            }
            break;
        default:
            break;
        }

        /* Simplify expressions for "shift/rot r, 0, a => movi r, 0",
           and "sub r, 0, a => neg r, a" case.  */
        switch (opc) {
        CASE_OP_32_64(shl):
        CASE_OP_32_64(shr):
        CASE_OP_32_64(sar):
        CASE_OP_32_64(rotl):
        CASE_OP_32_64(rotr):
            if (arg_is_const(op->args[1])
                && arg_info(op->args[1])->val == 0) {
                tcg_opt_gen_movi(s, op, op->args[0], 0);
                continue;
            }
            break;
        CASE_OP_32_64_VEC(sub):
            {
                TCGOpcode neg_op;
                bool have_neg;

                if (arg_is_const(op->args[2])) {
                    /* Proceed with possible constant folding. */
                    break;
                }
                if (opc == INDEX_op_sub_i32) {
                    neg_op = INDEX_op_neg_i32;
                    have_neg = TCG_TARGET_HAS_neg_i32;
                } else if (opc == INDEX_op_sub_i64) {
                    neg_op = INDEX_op_neg_i64;
                    have_neg = TCG_TARGET_HAS_neg_i64;
                } else {
                    neg_op = INDEX_op_neg_vec;
                    have_neg = TCG_TARGET_HAS_neg_vec;
                }
                if (!have_neg) {
                    break;
                }
                if (arg_is_const(op->args[1])
                    && arg_info(op->args[1])->val == 0) {
                    op->opc = neg_op;
                    reset_temp(op->args[0]);
                    op->args[1] = op->args[2];
                    continue;
                }
            }
            break;
        CASE_OP_32_64_VEC(xor):
        CASE_OP_32_64(nand):
            if (!arg_is_const(op->args[1])
                && arg_is_const(op->args[2])
                && arg_info(op->args[2])->val == -1) {
                i = 1;
                goto try_not;
            }
            break;
        CASE_OP_32_64(nor):
            if (!arg_is_const(op->args[1])
                && arg_is_const(op->args[2])
                && arg_info(op->args[2])->val == 0) {
                i = 1;
                goto try_not;
            }
            break;
        CASE_OP_32_64_VEC(andc):
            if (!arg_is_const(op->args[2])
                && arg_is_const(op->args[1])
                && arg_info(op->args[1])->val == -1) {
                i = 2;
                goto try_not;
            }
            break;
        CASE_OP_32_64_VEC(orc):
        CASE_OP_32_64(eqv):
            if (!arg_is_const(op->args[2])
                && arg_is_const(op->args[1])
                && arg_info(op->args[1])->val == 0) {
                i = 2;
                goto try_not;
            }
            break;
        try_not:
            {
                TCGOpcode not_op;
                bool have_not;

                if (def->flags & TCG_OPF_VECTOR) {
                    not_op = INDEX_op_not_vec;
                    have_not = TCG_TARGET_HAS_not_vec;
                } else if (def->flags & TCG_OPF_64BIT) {
                    not_op = INDEX_op_not_i64;
                    have_not = TCG_TARGET_HAS_not_i64;
                } else {
                    not_op = INDEX_op_not_i32;
                    have_not = TCG_TARGET_HAS_not_i32;
                }
                if (!have_not) {
                    break;
                }
                op->opc = not_op;
                reset_temp(op->args[0]);
                op->args[1] = op->args[i];
                continue;
            }
        default:
            break;
        }

        /* Simplify expression for "op r, a, const => mov r, a" cases */
        switch (opc) {
        CASE_OP_32_64_VEC(add):
        CASE_OP_32_64_VEC(sub):
        CASE_OP_32_64_VEC(or):
        CASE_OP_32_64_VEC(xor):
        CASE_OP_32_64_VEC(andc):
        CASE_OP_32_64(shl):
        CASE_OP_32_64(shr):
        CASE_OP_32_64(sar):
        CASE_OP_32_64(rotl):
        CASE_OP_32_64(rotr):
            if (!arg_is_const(op->args[1])
                && arg_is_const(op->args[2])
                && arg_info(op->args[2])->val == 0) {
                tcg_opt_gen_mov(s, op, op->args[0], op->args[1]);
                continue;
            }
            break;
        CASE_OP_32_64_VEC(and):
        CASE_OP_32_64_VEC(orc):
        CASE_OP_32_64(eqv):
            if (!arg_is_const(op->args[1])
                && arg_is_const(op->args[2])
                && arg_info(op->args[2])->val == -1) {
                tcg_opt_gen_mov(s, op, op->args[0], op->args[1]);
                continue;
            }
            break;
        default:
            break;
        }

        /* Simplify using known-zero bits. Currently only ops with a single
           output argument is supported. */
        mask = -1;
        affected = -1;
        switch (opc) {
        CASE_OP_32_64(ext8s):
            if ((arg_info(op->args[1])->mask & 0x80) != 0) {
                break;
            }
        CASE_OP_32_64(ext8u):
            mask = 0xff;
            goto and_const;
        CASE_OP_32_64(ext16s):
            if ((arg_info(op->args[1])->mask & 0x8000) != 0) {
                break;
            }
        CASE_OP_32_64(ext16u):
            mask = 0xffff;
            goto and_const;
        case INDEX_op_ext32s_i64:
            if ((arg_info(op->args[1])->mask & 0x80000000) != 0) {
                break;
            }
        case INDEX_op_ext32u_i64:
            mask = 0xffffffffU;
            goto and_const;

        CASE_OP_32_64(and):
            mask = arg_info(op->args[2])->mask;
            if (arg_is_const(op->args[2])) {
        and_const:
                affected = arg_info(op->args[1])->mask & ~mask;
            }
            mask = arg_info(op->args[1])->mask & mask;
            break;

        case INDEX_op_ext_i32_i64:
            if ((arg_info(op->args[1])->mask & 0x80000000) != 0) {
                break;
            }
        case INDEX_op_extu_i32_i64:
            /* We do not compute affected as it is a size changing op.  */
            mask = (uint32_t)arg_info(op->args[1])->mask;
            break;

        CASE_OP_32_64(andc):
            /* Known-zeros does not imply known-ones.  Therefore unless
               op->args[2] is constant, we can't infer anything from it.  */
            if (arg_is_const(op->args[2])) {
                mask = ~arg_info(op->args[2])->mask;
                goto and_const;
            }
            /* But we certainly know nothing outside args[1] may be set. */
            mask = arg_info(op->args[1])->mask;
            break;

        case INDEX_op_sar_i32:
            if (arg_is_const(op->args[2])) {
                tmp = arg_info(op->args[2])->val & 31;
                mask = (int32_t)arg_info(op->args[1])->mask >> tmp;
            }
            break;
        case INDEX_op_sar_i64:
            if (arg_is_const(op->args[2])) {
                tmp = arg_info(op->args[2])->val & 63;
                mask = (int64_t)arg_info(op->args[1])->mask >> tmp;
            }
            break;

        case INDEX_op_shr_i32:
            if (arg_is_const(op->args[2])) {
                tmp = arg_info(op->args[2])->val & 31;
                mask = (uint32_t)arg_info(op->args[1])->mask >> tmp;
            }
            break;
        case INDEX_op_shr_i64:
            if (arg_is_const(op->args[2])) {
                tmp = arg_info(op->args[2])->val & 63;
                mask = (uint64_t)arg_info(op->args[1])->mask >> tmp;
            }
            break;

        case INDEX_op_extrl_i64_i32:
            mask = (uint32_t)arg_info(op->args[1])->mask;
            break;
        case INDEX_op_extrh_i64_i32:
            mask = (uint64_t)arg_info(op->args[1])->mask >> 32;
            break;

        CASE_OP_32_64(shl):
            if (arg_is_const(op->args[2])) {
                tmp = arg_info(op->args[2])->val & (TCG_TARGET_REG_BITS - 1);
                mask = arg_info(op->args[1])->mask << tmp;
            }
            break;

        CASE_OP_32_64(neg):
            /* Set to 1 all bits to the left of the rightmost.  */
            mask = -(arg_info(op->args[1])->mask
                     & -arg_info(op->args[1])->mask);
            break;

        CASE_OP_32_64(deposit):
            mask = deposit64(arg_info(op->args[1])->mask,
                             op->args[3], op->args[4],
                             arg_info(op->args[2])->mask);
            break;

        CASE_OP_32_64(extract):
            mask = extract64(arg_info(op->args[1])->mask,
                             op->args[2], op->args[3]);
            if (op->args[2] == 0) {
                affected = arg_info(op->args[1])->mask & ~mask;
            }
            break;
        CASE_OP_32_64(sextract):
            mask = sextract64(arg_info(op->args[1])->mask,
                              op->args[2], op->args[3]);
            if (op->args[2] == 0 && (tcg_target_long)mask >= 0) {
                affected = arg_info(op->args[1])->mask & ~mask;
            }
            break;

        CASE_OP_32_64(or):
        CASE_OP_32_64(xor):
            mask = arg_info(op->args[1])->mask | arg_info(op->args[2])->mask;
            break;

        case INDEX_op_clz_i32:
        case INDEX_op_ctz_i32:
            mask = arg_info(op->args[2])->mask | 31;
            break;

        case INDEX_op_clz_i64:
        case INDEX_op_ctz_i64:
            mask = arg_info(op->args[2])->mask | 63;
            break;

        case INDEX_op_ctpop_i32:
            mask = 32 | 31;
            break;
        case INDEX_op_ctpop_i64:
            mask = 64 | 63;
            break;

        CASE_OP_32_64(setcond):
        case INDEX_op_setcond2_i32:
            mask = 1;
            break;

        CASE_OP_32_64(movcond):
            mask = arg_info(op->args[3])->mask | arg_info(op->args[4])->mask;
            break;

        CASE_OP_32_64(ld8u):
            mask = 0xff;
            break;
        CASE_OP_32_64(ld16u):
            mask = 0xffff;
            break;
        case INDEX_op_ld32u_i64:
            mask = 0xffffffffu;
            break;

        CASE_OP_32_64(qemu_ld):
            {
                TCGMemOpIdx oi = op->args[nb_oargs + nb_iargs];
                TCGMemOp mop = get_memop(oi);
                if (!(mop & MO_SIGN)) {
                    mask = (2ULL << ((8 << (mop & MO_SIZE)) - 1)) - 1;
                }
            }
            break;

        default:
            break;
        }

        /* 32-bit ops generate 32-bit results.  For the result is zero test
           below, we can ignore high bits, but for further optimizations we
           need to record that the high bits contain garbage.  */
        partmask = mask;
        if (!(def->flags & TCG_OPF_64BIT)) {
            mask |= ~(tcg_target_ulong)0xffffffffu;
            partmask &= 0xffffffffu;
            affected &= 0xffffffffu;
        }

        if (partmask == 0) {
            tcg_debug_assert(nb_oargs == 1);
            tcg_opt_gen_movi(s, op, op->args[0], 0);
            continue;
        }
        if (affected == 0) {
            tcg_debug_assert(nb_oargs == 1);
            tcg_opt_gen_mov(s, op, op->args[0], op->args[1]);
            continue;
        }

        /* Simplify expression for "op r, a, 0 => movi r, 0" cases */
        switch (opc) {
        CASE_OP_32_64_VEC(and):
        CASE_OP_32_64_VEC(mul):
        CASE_OP_32_64(muluh):
        CASE_OP_32_64(mulsh):
            if (arg_is_const(op->args[2])
                && arg_info(op->args[2])->val == 0) {
                tcg_opt_gen_movi(s, op, op->args[0], 0);
                continue;
            }
            break;
        default:
            break;
        }

        /* Simplify expression for "op r, a, a => mov r, a" cases */
        switch (opc) {
        CASE_OP_32_64_VEC(or):
        CASE_OP_32_64_VEC(and):
            if (args_are_copies(op->args[1], op->args[2])) {
                tcg_opt_gen_mov(s, op, op->args[0], op->args[1]);
                continue;
            }
            break;
        default:
            break;
        }

        /* Simplify expression for "op r, a, a => movi r, 0" cases */
        switch (opc) {
        CASE_OP_32_64_VEC(andc):
        CASE_OP_32_64_VEC(sub):
        CASE_OP_32_64_VEC(xor):
            if (args_are_copies(op->args[1], op->args[2])) {
                tcg_opt_gen_movi(s, op, op->args[0], 0);
                continue;
            }
            break;
        default:
            break;
        }

        /* Propagate constants through copy operations and do constant
           folding.  Constants will be substituted to arguments by register
           allocator where needed and possible.  Also detect copies. */
        switch (opc) {
        CASE_OP_32_64_VEC(mov):
            tcg_opt_gen_mov(s, op, op->args[0], op->args[1]);
            break;
        CASE_OP_32_64(movi):
        case INDEX_op_dupi_vec:
            tcg_opt_gen_movi(s, op, op->args[0], op->args[1]);
            break;

        case INDEX_op_dup_vec:
            if (arg_is_const(op->args[1])) {
                tmp = arg_info(op->args[1])->val;
                tmp = dup_const(TCGOP_VECE(op), tmp);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                continue;
            }
            break;

        CASE_OP_32_64(not):
        CASE_OP_32_64(neg):
        CASE_OP_32_64(ext8s):
        CASE_OP_32_64(ext8u):
        CASE_OP_32_64(ext16s):
        CASE_OP_32_64(ext16u):
        CASE_OP_32_64(ctpop):
        case INDEX_op_ext32s_i64:
        case INDEX_op_ext32u_i64:
        case INDEX_op_ext_i32_i64:
        case INDEX_op_extu_i32_i64:
        case INDEX_op_extrl_i64_i32:
        case INDEX_op_extrh_i64_i32:
            if (arg_is_const(op->args[1])) {
                tmp = do_constant_folding(opc, arg_info(op->args[1])->val, 0);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(add):
        CASE_OP_32_64(sub):
        CASE_OP_32_64(mul):
        CASE_OP_32_64(or):
        CASE_OP_32_64(and):
        CASE_OP_32_64(xor):
        CASE_OP_32_64(shl):
        CASE_OP_32_64(shr):
        CASE_OP_32_64(sar):
        CASE_OP_32_64(rotl):
        CASE_OP_32_64(rotr):
        CASE_OP_32_64(andc):
        CASE_OP_32_64(orc):
        CASE_OP_32_64(eqv):
        CASE_OP_32_64(nand):
        CASE_OP_32_64(nor):
        CASE_OP_32_64(muluh):
        CASE_OP_32_64(mulsh):
        CASE_OP_32_64(div):
        CASE_OP_32_64(divu):
        CASE_OP_32_64(rem):
        CASE_OP_32_64(remu):
            if (arg_is_const(op->args[1]) && arg_is_const(op->args[2])) {
                tmp = do_constant_folding(opc, arg_info(op->args[1])->val,
                                          arg_info(op->args[2])->val);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(clz):
        CASE_OP_32_64(ctz):
            if (arg_is_const(op->args[1])) {
                TCGArg v = arg_info(op->args[1])->val;
                if (v != 0) {
                    tmp = do_constant_folding(opc, v, 0);
                    tcg_opt_gen_movi(s, op, op->args[0], tmp);
                } else {
                    tcg_opt_gen_mov(s, op, op->args[0], op->args[2]);
                }
                break;
            }
            goto do_default;

        CASE_OP_32_64(deposit):
            if (arg_is_const(op->args[1]) && arg_is_const(op->args[2])) {
                tmp = deposit64(arg_info(op->args[1])->val,
                                op->args[3], op->args[4],
                                arg_info(op->args[2])->val);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(extract):
            if (arg_is_const(op->args[1])) {
                tmp = extract64(arg_info(op->args[1])->val,
                                op->args[2], op->args[3]);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(sextract):
            if (arg_is_const(op->args[1])) {
                tmp = sextract64(arg_info(op->args[1])->val,
                                 op->args[2], op->args[3]);
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(setcond):
            tmp = do_constant_folding_cond(opc, op->args[1],
                                           op->args[2], op->args[3]);
            if (tmp != 2) {
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
                break;
            }
            goto do_default;

        CASE_OP_32_64(brcond):
            tmp = do_constant_folding_cond(opc, op->args[0],
                                           op->args[1], op->args[2]);
            if (tmp != 2) {
                if (tmp) {
                    bitmap_zero(temps_used.l, nb_temps);
                    op->opc = INDEX_op_br;
                    op->args[0] = op->args[3];
                } else {
                    tcg_op_remove(s, op);
                }
                break;
            }
            goto do_default;

        CASE_OP_32_64(movcond):
            tmp = do_constant_folding_cond(opc, op->args[1],
                                           op->args[2], op->args[5]);
            if (tmp != 2) {
                tcg_opt_gen_mov(s, op, op->args[0], op->args[4-tmp]);
                break;
            }
            if (arg_is_const(op->args[3]) && arg_is_const(op->args[4])) {
                tcg_target_ulong tv = arg_info(op->args[3])->val;
                tcg_target_ulong fv = arg_info(op->args[4])->val;
                TCGCond cond = op->args[5];
                if (fv == 1 && tv == 0) {
                    cond = tcg_invert_cond(cond);
                } else if (!(tv == 1 && fv == 0)) {
                    goto do_default;
                }
                op->args[3] = cond;
                op->opc = opc = (opc == INDEX_op_movcond_i32
                                 ? INDEX_op_setcond_i32
                                 : INDEX_op_setcond_i64);
                nb_iargs = 2;
            }
            goto do_default;

        case INDEX_op_add2_i32:
        case INDEX_op_sub2_i32:
            if (arg_is_const(op->args[2]) && arg_is_const(op->args[3])
                && arg_is_const(op->args[4]) && arg_is_const(op->args[5])) {
                uint32_t al = arg_info(op->args[2])->val;
                uint32_t ah = arg_info(op->args[3])->val;
                uint32_t bl = arg_info(op->args[4])->val;
                uint32_t bh = arg_info(op->args[5])->val;
                uint64_t a = ((uint64_t)ah << 32) | al;
                uint64_t b = ((uint64_t)bh << 32) | bl;
                TCGArg rl, rh;
                TCGOp *op2 = tcg_op_insert_before(s, op, INDEX_op_movi_i32, 2);

                if (opc == INDEX_op_add2_i32) {
                    a += b;
                } else {
                    a -= b;
                }

                rl = op->args[0];
                rh = op->args[1];
                tcg_opt_gen_movi(s, op, rl, (int32_t)a);
                tcg_opt_gen_movi(s, op2, rh, (int32_t)(a >> 32));
                break;
            }
            goto do_default;

        case INDEX_op_mulu2_i32:
            if (arg_is_const(op->args[2]) && arg_is_const(op->args[3])) {
                uint32_t a = arg_info(op->args[2])->val;
                uint32_t b = arg_info(op->args[3])->val;
                uint64_t r = (uint64_t)a * b;
                TCGArg rl, rh;
                TCGOp *op2 = tcg_op_insert_before(s, op, INDEX_op_movi_i32, 2);

                rl = op->args[0];
                rh = op->args[1];
                tcg_opt_gen_movi(s, op, rl, (int32_t)r);
                tcg_opt_gen_movi(s, op2, rh, (int32_t)(r >> 32));
                break;
            }
            goto do_default;

        case INDEX_op_brcond2_i32:
            tmp = do_constant_folding_cond2(&op->args[0], &op->args[2],
                                            op->args[4]);
            if (tmp != 2) {
                if (tmp) {
            do_brcond_true:
                    bitmap_zero(temps_used.l, nb_temps);
                    op->opc = INDEX_op_br;
                    op->args[0] = op->args[5];
                } else {
            do_brcond_false:
                    tcg_op_remove(s, op);
                }
            } else if ((op->args[4] == TCG_COND_LT
                        || op->args[4] == TCG_COND_GE)
                       && arg_is_const(op->args[2])
                       && arg_info(op->args[2])->val == 0
                       && arg_is_const(op->args[3])
                       && arg_info(op->args[3])->val == 0) {
                /* Simplify LT/GE comparisons vs zero to a single compare
                   vs the high word of the input.  */
            do_brcond_high:
                bitmap_zero(temps_used.l, nb_temps);
                op->opc = INDEX_op_brcond_i32;
                op->args[0] = op->args[1];
                op->args[1] = op->args[3];
                op->args[2] = op->args[4];
                op->args[3] = op->args[5];
            } else if (op->args[4] == TCG_COND_EQ) {
                /* Simplify EQ comparisons where one of the pairs
                   can be simplified.  */
                tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
                                               op->args[0], op->args[2],
                                               TCG_COND_EQ);
                if (tmp == 0) {
                    goto do_brcond_false;
                } else if (tmp == 1) {
                    goto do_brcond_high;
                }
                tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
                                               op->args[1], op->args[3],
                                               TCG_COND_EQ);
                if (tmp == 0) {
                    goto do_brcond_false;
                } else if (tmp != 1) {
                    goto do_default;
                }
            do_brcond_low:
                bitmap_zero(temps_used.l, nb_temps);
                op->opc = INDEX_op_brcond_i32;
                op->args[1] = op->args[2];
                op->args[2] = op->args[4];
                op->args[3] = op->args[5];
            } else if (op->args[4] == TCG_COND_NE) {
                /* Simplify NE comparisons where one of the pairs
                   can be simplified.  */
                tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
                                               op->args[0], op->args[2],
                                               TCG_COND_NE);
                if (tmp == 0) {
                    goto do_brcond_high;
                } else if (tmp == 1) {
                    goto do_brcond_true;
                }
                tmp = do_constant_folding_cond(INDEX_op_brcond_i32,
                                               op->args[1], op->args[3],
                                               TCG_COND_NE);
                if (tmp == 0) {
                    goto do_brcond_low;
                } else if (tmp == 1) {
                    goto do_brcond_true;
                }
                goto do_default;
            } else {
                goto do_default;
            }
            break;

        case INDEX_op_setcond2_i32:
            tmp = do_constant_folding_cond2(&op->args[1], &op->args[3],
                                            op->args[5]);
            if (tmp != 2) {
            do_setcond_const:
                tcg_opt_gen_movi(s, op, op->args[0], tmp);
            } else if ((op->args[5] == TCG_COND_LT
                        || op->args[5] == TCG_COND_GE)
                       && arg_is_const(op->args[3])
                       && arg_info(op->args[3])->val == 0
                       && arg_is_const(op->args[4])
                       && arg_info(op->args[4])->val == 0) {
                /* Simplify LT/GE comparisons vs zero to a single compare
                   vs the high word of the input.  */
            do_setcond_high:
                reset_temp(op->args[0]);
                arg_info(op->args[0])->mask = 1;
                op->opc = INDEX_op_setcond_i32;
                op->args[1] = op->args[2];
                op->args[2] = op->args[4];
                op->args[3] = op->args[5];
            } else if (op->args[5] == TCG_COND_EQ) {
                /* Simplify EQ comparisons where one of the pairs
                   can be simplified.  */
                tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
                                               op->args[1], op->args[3],
                                               TCG_COND_EQ);
                if (tmp == 0) {
                    goto do_setcond_const;
                } else if (tmp == 1) {
                    goto do_setcond_high;
                }
                tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
                                               op->args[2], op->args[4],
                                               TCG_COND_EQ);
                if (tmp == 0) {
                    goto do_setcond_high;
                } else if (tmp != 1) {
                    goto do_default;
                }
            do_setcond_low:
                reset_temp(op->args[0]);
                arg_info(op->args[0])->mask = 1;
                op->opc = INDEX_op_setcond_i32;
                op->args[2] = op->args[3];
                op->args[3] = op->args[5];
            } else if (op->args[5] == TCG_COND_NE) {
                /* Simplify NE comparisons where one of the pairs
                   can be simplified.  */
                tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
                                               op->args[1], op->args[3],
                                               TCG_COND_NE);
                if (tmp == 0) {
                    goto do_setcond_high;
                } else if (tmp == 1) {
                    goto do_setcond_const;
                }
                tmp = do_constant_folding_cond(INDEX_op_setcond_i32,
                                               op->args[2], op->args[4],
                                               TCG_COND_NE);
                if (tmp == 0) {
                    goto do_setcond_low;
                } else if (tmp == 1) {
                    goto do_setcond_const;
                }
                goto do_default;
            } else {
                goto do_default;
            }
            break;

        case INDEX_op_call:
            if (!(op->args[nb_oargs + nb_iargs + 1]
                  & (TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_WRITE_GLOBALS))) {
                for (i = 0; i < nb_globals; i++) {
                    if (test_bit(i, temps_used.l)) {
                        reset_ts(&s->temps[i]);
                    }
                }
            }
            goto do_reset_output;

        default:
        do_default:
            /* Default case: we know nothing about operation (or were unable
               to compute the operation result) so no propagation is done.
               We trash everything if the operation is the end of a basic
               block, otherwise we only trash the output args.  "mask" is
               the non-zero bits mask for the first output arg.  */
            if (def->flags & TCG_OPF_BB_END) {
                bitmap_zero(temps_used.l, nb_temps);
            } else {
        do_reset_output:
                for (i = 0; i < nb_oargs; i++) {
                    reset_temp(op->args[i]);
                    /* Save the corresponding known-zero bits mask for the
                       first output argument (only one supported so far). */
                    if (i == 0) {
                        arg_info(op->args[i])->mask = mask;
                    }
                }
            }
            break;
        }

        /* Eliminate duplicate and redundant fence instructions.  */
        if (prev_mb) {
            switch (opc) {
            case INDEX_op_mb:
                /* Merge two barriers of the same type into one,
                 * or a weaker barrier into a stronger one,
                 * or two weaker barriers into a stronger one.
                 *   mb X; mb Y => mb X|Y
                 *   mb; strl => mb; st
                 *   ldaq; mb => ld; mb
                 *   ldaq; strl => ld; mb; st
                 * Other combinations are also merged into a strong
                 * barrier.  This is stricter than specified but for
                 * the purposes of TCG is better than not optimizing.
                 */
                prev_mb->args[0] |= op->args[0];
                tcg_op_remove(s, op);
                break;

            default:
                /* Opcodes that end the block stop the optimization.  */
                if ((def->flags & TCG_OPF_BB_END) == 0) {
                    break;
                }
                /* fallthru */
            case INDEX_op_qemu_ld_i32:
            case INDEX_op_qemu_ld_i64:
            case INDEX_op_qemu_st_i32:
            case INDEX_op_qemu_st_i64:
            case INDEX_op_call:
                /* Opcodes that touch guest memory stop the optimization.  */
                prev_mb = NULL;
                break;
            }
        } else if (opc == INDEX_op_mb) {
            prev_mb = op;
        }
    }
}