8534112221

Committed 03 Apr 2024 06:07AM UTC coverage: 92.607% (+0.02%) from 92.583%

Build # 8534112221

Build Type

push

github

Committed by

Buristan

Commit Message

Prevent down-recursion for side traces.

Thanks to Sergey Kaplun.

(cherry picked from commit cae361187)

Assume we have the root trace that uses some spill slots with the
corresponding stack adjustment. Then its side trace will restore the
stack only at its tail. It may look like the following:

| ---- TRACE 4 mcode 1247
| 55557f7df953  mov rax, [r14-0xe28]
| 55557f7df95a  mov rax, [rax+0x30]
| 55557f7df95e  sub rax, rdx
| 55557f7df961  cmp rax, +0x68
| 55557f7df965  jb 0x55557f7d004c       ->0
| 55557f7df96b  add rsp, -0x10
| ...
| 55557f6efa71  cmp dword [rdx+0x4], -0x05
| 55557f6efa75  jnz 0x55557f6e004c      ->0
| ...
| 55557f7dfe29  add rsp, +0x10
| 55557f7dfe2d  jmp 0x5555556fe573
| ---- TRACE 4 stop -> stitch
|
| ---- TRACE 5 start 4/0
| ---- TRACE 5 mcode 101
| 55557f6ef9d4  mov dword [0x40000518], 0x5
| ...
| 55557f6efa30  add rsp, +0x10
| 55557f6efa34  jmp 0x55557f6ef9d4
| ---- TRACE 5 stop -> down-recursion

Such side traces have no stack adjustment at their heads since their
stack adjustment is inherited from the parent trace. The issue occurs if
the side trace has a down-recursion, as mentioned above. Before any
exit, we can jump back to the start of the trace several times with
growing `rsp`. In that case, the `rsp` is restored incorrectly after
exiting from the trace.

This patch forbids down-recursion for non-root traces.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#9595

Run Details

5660 of 6018 branches covered (94.05%)

Branch coverage included in aggregate %.

1 of 1 new or added line in 1 file covered. (100.0%)

12 existing lines in 4 files now uncovered.

21598 of 23416 relevant lines covered (92.24%)

2926632.1 hits per line

Source File
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96.7

/src/lj_asm.c

/*
** IR assembler (SSA IR -> machine code).
** Copyright (C) 2005-2017 Mike Pall. See Copyright Notice in luajit.h
*/

#define lj_asm_c
#define LUA_CORE

#include "lj_obj.h"

#if LJ_HASJIT

#include "lj_gc.h"
#include "lj_str.h"
#include "lj_tab.h"
#include "lj_frame.h"
#if LJ_HASFFI
#include "lj_ctype.h"
#endif
#include "lj_ir.h"
#include "lj_jit.h"
#include "lj_ircall.h"
#include "lj_iropt.h"
#include "lj_mcode.h"
#include "lj_iropt.h"
#include "lj_trace.h"
#include "lj_snap.h"
#include "lj_asm.h"
#include "lj_dispatch.h"
#include "lj_vm.h"
#include "lj_target.h"

#ifdef LUA_USE_ASSERT
#include <stdio.h>
#endif

/* -- Assembler state and common macros ----------------------------------- */

/* Assembler state. */
typedef struct ASMState {
  RegCost cost[RID_MAX];  /* Reference and blended allocation cost for regs. */

  MCode *mcp;                /* Current MCode pointer (grows down). */
  MCode *mclim;                /* Lower limit for MCode memory + red zone. */
#ifdef LUA_USE_ASSERT
  MCode *mcp_prev;        /* Red zone overflow check. */
#endif

  IRIns *ir;                /* Copy of pointer to IR instructions/constants. */
  jit_State *J;                /* JIT compiler state. */

#if LJ_TARGET_X86ORX64
  x86ModRM mrm;                /* Fused x86 address operand. */
#endif

  RegSet freeset;        /* Set of free registers. */
  RegSet modset;        /* Set of registers modified inside the loop. */
  RegSet weakset;        /* Set of weakly referenced registers. */
  RegSet phiset;        /* Set of PHI registers. */

  uint32_t flags;        /* Copy of JIT compiler flags. */
  int loopinv;                /* Loop branch inversion (0:no, 1:yes, 2:yes+CC_P). */

  int32_t evenspill;        /* Next even spill slot. */
  int32_t oddspill;        /* Next odd spill slot (or 0). */

  IRRef curins;                /* Reference of current instruction. */
  IRRef stopins;        /* Stop assembly before hitting this instruction. */
  IRRef orignins;        /* Original T->nins. */

  IRRef snapref;        /* Current snapshot is active after this reference. */
  IRRef snaprename;        /* Rename highwater mark for snapshot check. */
  SnapNo snapno;        /* Current snapshot number. */
  SnapNo loopsnapno;        /* Loop snapshot number. */
  BloomFilter snapfilt1, snapfilt2;        /* Filled with snapshot refs. */
  int snapalloc;        /* Current snapshot needs allocation. */

  IRRef fuseref;        /* Fusion limit (loopref, 0 or FUSE_DISABLED). */
  IRRef sectref;        /* Section base reference (loopref or 0). */
  IRRef loopref;        /* Reference of LOOP instruction (or 0). */

  BCReg topslot;        /* Number of slots for stack check (unless 0). */
  int32_t gcsteps;        /* Accumulated number of GC steps (per section). */

  GCtrace *T;                /* Trace to assemble. */
  GCtrace *parent;        /* Parent trace (or NULL). */

  MCode *mcbot;                /* Bottom of reserved MCode. */
  MCode *mctop;                /* Top of generated MCode. */
  MCode *mctoporig;        /* Original top of generated MCode. */
  MCode *mcloop;        /* Pointer to loop MCode (or NULL). */
  MCode *invmcp;        /* Points to invertible loop branch (or NULL). */
  MCode *flagmcp;        /* Pending opportunity to merge flag setting ins. */
  MCode *realign;        /* Realign loop if not NULL. */

#ifdef RID_NUM_KREF
  intptr_t krefk[RID_NUM_KREF];
#endif
  IRRef1 phireg[RID_MAX];  /* PHI register references. */
  uint16_t parentmap[LJ_MAX_JSLOTS];  /* Parent instruction to RegSP map. */
} ASMState;

#ifdef LUA_USE_ASSERT
#define lj_assertA(c, ...)        lj_assertG_(J2G(as->J), (c), __VA_ARGS__)
#else
#define lj_assertA(c, ...)        ((void)as)
#endif

#define IR(ref)                        (&as->ir[(ref)])

#define ASMREF_TMP1                REF_TRUE        /* Temp. register. */
#define ASMREF_TMP2                REF_FALSE        /* Temp. register. */
#define ASMREF_L                REF_NIL                /* Stores register for L. */

/* Check for variant to invariant references. */
#define iscrossref(as, ref)        ((ref) < as->sectref)

/* Inhibit memory op fusion from variant to invariant references. */
#define FUSE_DISABLED                (~(IRRef)0)
#define mayfuse(as, ref)        ((ref) > as->fuseref)
#define neverfuse(as)                (as->fuseref == FUSE_DISABLED)
#define canfuse(as, ir)                (!neverfuse(as) && !irt_isphi((ir)->t))
#define opisfusableload(o) \
  ((o) == IR_ALOAD || (o) == IR_HLOAD || (o) == IR_ULOAD || \
   (o) == IR_FLOAD || (o) == IR_XLOAD || (o) == IR_SLOAD || (o) == IR_VLOAD)

/* Sparse limit checks using a red zone before the actual limit. */
#define MCLIM_REDZONE        64

static LJ_NORET LJ_NOINLINE void asm_mclimit(ASMState *as)
{
  lj_mcode_limiterr(as->J, (size_t)(as->mctop - as->mcp + 4*MCLIM_REDZONE));
}

static LJ_AINLINE void checkmclim(ASMState *as)
{
#ifdef LUA_USE_ASSERT
  if (as->mcp + MCLIM_REDZONE < as->mcp_prev) {
    IRIns *ir = IR(as->curins+1);
    lj_assertA(0, "red zone overflow: %p IR %04d  %02d %04d %04d\n", as->mcp,
      as->curins+1-REF_BIAS, ir->o, ir->op1-REF_BIAS, ir->op2-REF_BIAS);
  }
#endif
  if (LJ_UNLIKELY(as->mcp < as->mclim)) asm_mclimit(as);
#ifdef LUA_USE_ASSERT
  as->mcp_prev = as->mcp;
#endif
}

#ifdef RID_NUM_KREF
#define ra_iskref(ref)                ((ref) < RID_NUM_KREF)
#define ra_krefreg(ref)                ((Reg)(RID_MIN_KREF + (Reg)(ref)))
#define ra_krefk(as, ref)        (as->krefk[(ref)])

static LJ_AINLINE void ra_setkref(ASMState *as, Reg r, intptr_t k)
{
  IRRef ref = (IRRef)(r - RID_MIN_KREF);
  as->krefk[ref] = k;
  as->cost[r] = REGCOST(ref, ref);
}

#else
#define ra_iskref(ref)                0
#define ra_krefreg(ref)                RID_MIN_GPR
#define ra_krefk(as, ref)        0
#endif

/* Arch-specific field offsets. */
static const uint8_t field_ofs[IRFL__MAX+1] = {
#define FLOFS(name, ofs)        (uint8_t)(ofs),
IRFLDEF(FLOFS)
#undef FLOFS
  0
};

/* -- Target-specific instruction emitter --------------------------------- */

#if LJ_TARGET_X86ORX64
#include "lj_emit_x86.h"
#elif LJ_TARGET_ARM
#include "lj_emit_arm.h"
#elif LJ_TARGET_ARM64
#include "lj_emit_arm64.h"
#elif LJ_TARGET_PPC
#include "lj_emit_ppc.h"
#elif LJ_TARGET_MIPS
#include "lj_emit_mips.h"
#else
#error "Missing instruction emitter for target CPU"
#endif

/* Generic load/store of register from/to stack slot. */
#define emit_spload(as, ir, r, ofs) \
  emit_loadofs(as, ir, (r), RID_SP, (ofs))
#define emit_spstore(as, ir, r, ofs) \
  emit_storeofs(as, ir, (r), RID_SP, (ofs))

/* -- Register allocator debugging ---------------------------------------- */

/* #define LUAJIT_DEBUG_RA */

#ifdef LUAJIT_DEBUG_RA

#include <stdio.h>
#include <stdarg.h>

#define RIDNAME(name)        #name,
static const char *const ra_regname[] = {
  GPRDEF(RIDNAME)
  FPRDEF(RIDNAME)
  VRIDDEF(RIDNAME)
  NULL
};
#undef RIDNAME

static char ra_dbg_buf[65536];
static char *ra_dbg_p;
static char *ra_dbg_merge;
static MCode *ra_dbg_mcp;

static void ra_dstart(void)
{
  ra_dbg_p = ra_dbg_buf;
  ra_dbg_merge = NULL;
  ra_dbg_mcp = NULL;
}

static void ra_dflush(void)
{
  fwrite(ra_dbg_buf, 1, (size_t)(ra_dbg_p-ra_dbg_buf), stdout);
  ra_dstart();
}

static void ra_dprintf(ASMState *as, const char *fmt, ...)
{
  char *p;
  va_list argp;
  va_start(argp, fmt);
  p = ra_dbg_mcp == as->mcp ? ra_dbg_merge : ra_dbg_p;
  ra_dbg_mcp = NULL;
  p += sprintf(p, "%08x  \e[36m%04d ", (uintptr_t)as->mcp, as->curins-REF_BIAS);
  for (;;) {
    const char *e = strchr(fmt, '$');
    if (e == NULL) break;
    memcpy(p, fmt, (size_t)(e-fmt));
    p += e-fmt;
    if (e[1] == 'r') {
      Reg r = va_arg(argp, Reg) & RID_MASK;
      if (r <= RID_MAX) {
        const char *q;
        for (q = ra_regname[r]; *q; q++)
          *p++ = *q >= 'A' && *q <= 'Z' ? *q + 0x20 : *q;
      } else {
        *p++ = '?';
        lj_assertA(0, "bad register %d for debug format \"%s\"", r, fmt);
      }
    } else if (e[1] == 'f' || e[1] == 'i') {
      IRRef ref;
      if (e[1] == 'f')
        ref = va_arg(argp, IRRef);
      else
        ref = va_arg(argp, IRIns *) - as->ir;
      if (ref >= REF_BIAS)
        p += sprintf(p, "%04d", ref - REF_BIAS);
      else
        p += sprintf(p, "K%03d", REF_BIAS - ref);
    } else if (e[1] == 's') {
      uint32_t slot = va_arg(argp, uint32_t);
      p += sprintf(p, "[sp+0x%x]", sps_scale(slot));
    } else if (e[1] == 'x') {
      p += sprintf(p, "%08x", va_arg(argp, int32_t));
    } else {
      lj_assertA(0, "bad debug format code");
    }
    fmt = e+2;
  }
  va_end(argp);
  while (*fmt)
    *p++ = *fmt++;
  *p++ = '\e'; *p++ = '['; *p++ = 'm'; *p++ = '\n';
  if (p > ra_dbg_buf+sizeof(ra_dbg_buf)-256) {
    fwrite(ra_dbg_buf, 1, (size_t)(p-ra_dbg_buf), stdout);
    p = ra_dbg_buf;
  }
  ra_dbg_p = p;
}

#define RA_DBG_START()        ra_dstart()
#define RA_DBG_FLUSH()        ra_dflush()
#define RA_DBG_REF() \
  do { char *_p = ra_dbg_p; ra_dprintf(as, ""); \
       ra_dbg_merge = _p; ra_dbg_mcp = as->mcp; } while (0)
#define RA_DBGX(x)        ra_dprintf x

#else
#define RA_DBG_START()        ((void)0)
#define RA_DBG_FLUSH()        ((void)0)
#define RA_DBG_REF()        ((void)0)
#define RA_DBGX(x)        ((void)0)
#endif

/* -- Register allocator -------------------------------------------------- */

#define ra_free(as, r)                rset_set(as->freeset, (r))
#define ra_modified(as, r)        rset_set(as->modset, (r))
#define ra_weak(as, r)                rset_set(as->weakset, (r))
#define ra_noweak(as, r)        rset_clear(as->weakset, (r))

#define ra_used(ir)                (ra_hasreg((ir)->r) || ra_hasspill((ir)->s))

/* Setup register allocator. */
static void ra_setup(ASMState *as)
{
  Reg r;
  /* Initially all regs (except the stack pointer) are free for use. */
  as->freeset = RSET_INIT;
  as->modset = RSET_EMPTY;
  as->weakset = RSET_EMPTY;
  as->phiset = RSET_EMPTY;
  memset(as->phireg, 0, sizeof(as->phireg));
  for (r = RID_MIN_GPR; r < RID_MAX; r++)
    as->cost[r] = REGCOST(~0u, 0u);
}

/* Rematerialize constants. */
static Reg ra_rematk(ASMState *as, IRRef ref)
{
  IRIns *ir;
  Reg r;
  if (ra_iskref(ref)) {
    r = ra_krefreg(ref);
    lj_assertA(!rset_test(as->freeset, r), "rematk of free reg %d", r);
    ra_free(as, r);
    ra_modified(as, r);
#if LJ_64
    emit_loadu64(as, r, ra_krefk(as, ref));
#else
    emit_loadi(as, r, ra_krefk(as, ref));
#endif
    return r;
  }
  ir = IR(ref);
  r = ir->r;
  lj_assertA(ra_hasreg(r), "rematk of K%03d has no reg", REF_BIAS - ref);
  lj_assertA(!ra_hasspill(ir->s),
             "rematk of K%03d has spill slot [%x]", REF_BIAS - ref, ir->s);
  ra_free(as, r);
  ra_modified(as, r);
  ir->r = RID_INIT;  /* Do not keep any hint. */
  RA_DBGX((as, "remat     $i $r", ir, r));
#if !LJ_SOFTFP32
  if (ir->o == IR_KNUM) {
    emit_loadk64(as, r, ir);
  } else
#endif
  if (emit_canremat(REF_BASE) && ir->o == IR_BASE) {
    ra_sethint(ir->r, RID_BASE);  /* Restore BASE register hint. */
    emit_getgl(as, r, jit_base);
  } else if (emit_canremat(ASMREF_L) && ir->o == IR_KPRI) {
    /* REF_NIL stores ASMREF_L register. */
    lj_assertA(irt_isnil(ir->t), "rematk of bad ASMREF_L");
    emit_getgl(as, r, cur_L);
#if LJ_64
  } else if (ir->o == IR_KINT64) {
    emit_loadu64(as, r, ir_kint64(ir)->u64);
#if LJ_GC64
  } else if (ir->o == IR_KGC) {
    emit_loadu64(as, r, (uintptr_t)ir_kgc(ir));
  } else if (ir->o == IR_KPTR || ir->o == IR_KKPTR) {
    emit_loadu64(as, r, (uintptr_t)ir_kptr(ir));
#endif
#endif
  } else {
    lj_assertA(ir->o == IR_KINT || ir->o == IR_KGC ||
               ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL,
               "rematk of bad IR op %d", ir->o);
    emit_loadi(as, r, ir->i);
  }
  return r;
}

/* Force a spill. Allocate a new spill slot if needed. */
static int32_t ra_spill(ASMState *as, IRIns *ir)
{
  int32_t slot = ir->s;
  lj_assertA(ir >= as->ir + REF_TRUE,
             "spill of K%03d", REF_BIAS - (int)(ir - as->ir));
  if (!ra_hasspill(slot)) {
    if (irt_is64(ir->t)) {
      slot = as->evenspill;
      as->evenspill += 2;
    } else if (as->oddspill) {
      slot = as->oddspill;
      as->oddspill = 0;
    } else {
      slot = as->evenspill;
      as->oddspill = slot+1;
      as->evenspill += 2;
    }
    if (as->evenspill > 256)
      lj_trace_err(as->J, LJ_TRERR_SPILLOV);
    ir->s = (uint8_t)slot;
  }
  return sps_scale(slot);
}

/* Release the temporarily allocated register in ASMREF_TMP1/ASMREF_TMP2. */
static Reg ra_releasetmp(ASMState *as, IRRef ref)
{
  IRIns *ir = IR(ref);
  Reg r = ir->r;
  lj_assertA(ra_hasreg(r), "release of TMP%d has no reg", ref-ASMREF_TMP1+1);
  lj_assertA(!ra_hasspill(ir->s),
             "release of TMP%d has spill slot [%x]", ref-ASMREF_TMP1+1, ir->s);
  ra_free(as, r);
  ra_modified(as, r);
  ir->r = RID_INIT;
  return r;
}

/* Restore a register (marked as free). Rematerialize or force a spill. */
static Reg ra_restore(ASMState *as, IRRef ref)
{
  if (emit_canremat(ref)) {
    return ra_rematk(as, ref);
  } else {
    IRIns *ir = IR(ref);
    int32_t ofs = ra_spill(as, ir);  /* Force a spill slot. */
    Reg r = ir->r;
    lj_assertA(ra_hasreg(r), "restore of IR %04d has no reg", ref - REF_BIAS);
    ra_sethint(ir->r, r);  /* Keep hint. */
    ra_free(as, r);
    if (!rset_test(as->weakset, r)) {  /* Only restore non-weak references. */
      ra_modified(as, r);
      RA_DBGX((as, "restore   $i $r", ir, r));
      emit_spload(as, ir, r, ofs);
    }
    return r;
  }
}

/* Save a register to a spill slot. */
static void ra_save(ASMState *as, IRIns *ir, Reg r)
{
  RA_DBGX((as, "save      $i $r", ir, r));
  emit_spstore(as, ir, r, sps_scale(ir->s));
}

#define MINCOST(name) \
  if (rset_test(RSET_ALL, RID_##name) && \
      LJ_LIKELY(allow&RID2RSET(RID_##name)) && as->cost[RID_##name] < cost) \
    cost = as->cost[RID_##name];

/* Evict the register with the lowest cost, forcing a restore. */
static Reg ra_evict(ASMState *as, RegSet allow)
{
  IRRef ref;
  RegCost cost = ~(RegCost)0;
  lj_assertA(allow != RSET_EMPTY, "evict from empty set");
  if (RID_NUM_FPR == 0 || allow < RID2RSET(RID_MAX_GPR)) {
    GPRDEF(MINCOST)
  } else {
    FPRDEF(MINCOST)
  }
  ref = regcost_ref(cost);
  lj_assertA(ra_iskref(ref) || (ref >= as->T->nk && ref < as->T->nins),
             "evict of out-of-range IR %04d", ref - REF_BIAS);
  /* Preferably pick any weak ref instead of a non-weak, non-const ref. */
  if (!irref_isk(ref) && (as->weakset & allow)) {
    IRIns *ir = IR(ref);
    if (!rset_test(as->weakset, ir->r))
      ref = regcost_ref(as->cost[rset_pickbot((as->weakset & allow))]);
  }
  return ra_restore(as, ref);
}

/* Pick any register (marked as free). Evict on-demand. */
static Reg ra_pick(ASMState *as, RegSet allow)
{
  RegSet pick = as->freeset & allow;
  if (!pick)
    return ra_evict(as, allow);
  else
    return rset_picktop(pick);
}

/* Get a scratch register (marked as free). */
static Reg ra_scratch(ASMState *as, RegSet allow)
{
  Reg r = ra_pick(as, allow);
  ra_modified(as, r);
  RA_DBGX((as, "scratch        $r", r));
  return r;
}

/* Evict all registers from a set (if not free). */
static void ra_evictset(ASMState *as, RegSet drop)
{
  RegSet work;
  as->modset |= drop;
#if !LJ_SOFTFP
  work = (drop & ~as->freeset) & RSET_FPR;
  while (work) {
    Reg r = rset_pickbot(work);
    ra_restore(as, regcost_ref(as->cost[r]));
    rset_clear(work, r);
    checkmclim(as);
  }
#endif
  work = (drop & ~as->freeset);
  while (work) {
    Reg r = rset_pickbot(work);
    ra_restore(as, regcost_ref(as->cost[r]));
    rset_clear(work, r);
    checkmclim(as);
  }
}

/* Evict (rematerialize) all registers allocated to constants. */
static void ra_evictk(ASMState *as)
{
  RegSet work;
#if !LJ_SOFTFP
  work = ~as->freeset & RSET_FPR;
  while (work) {
    Reg r = rset_pickbot(work);
    IRRef ref = regcost_ref(as->cost[r]);
    if (emit_canremat(ref) && irref_isk(ref)) {
      ra_rematk(as, ref);
      checkmclim(as);
    }
    rset_clear(work, r);
  }
#endif
  work = ~as->freeset & RSET_GPR;
  while (work) {
    Reg r = rset_pickbot(work);
    IRRef ref = regcost_ref(as->cost[r]);
    if (emit_canremat(ref) && irref_isk(ref)) {
      ra_rematk(as, ref);
      checkmclim(as);
    }
    rset_clear(work, r);
  }
}

#ifdef RID_NUM_KREF
/* Allocate a register for a constant. */
static Reg ra_allock(ASMState *as, intptr_t k, RegSet allow)
{
  /* First try to find a register which already holds the same constant. */
  RegSet pick, work = ~as->freeset & RSET_GPR;
  Reg r;
  while (work) {
    IRRef ref;
    r = rset_pickbot(work);
    ref = regcost_ref(as->cost[r]);
#if LJ_64
    if (ref < ASMREF_L) {
      if (ra_iskref(ref)) {
        if (k == ra_krefk(as, ref))
          return r;
      } else {
        IRIns *ir = IR(ref);
        if ((ir->o == IR_KINT64 && k == (int64_t)ir_kint64(ir)->u64) ||
#if LJ_GC64
            (ir->o == IR_KINT && k == ir->i) ||
            (ir->o == IR_KGC && k == (intptr_t)ir_kgc(ir)) ||
            ((ir->o == IR_KPTR || ir->o == IR_KKPTR) &&
             k == (intptr_t)ir_kptr(ir))
#else
            (ir->o != IR_KINT64 && k == ir->i)
#endif
           )
          return r;
      }
    }
#else
    if (ref < ASMREF_L &&
        k == (ra_iskref(ref) ? ra_krefk(as, ref) : IR(ref)->i))
      return r;
#endif
    rset_clear(work, r);
  }
  pick = as->freeset & allow;
  if (pick) {
    /* Constants should preferably get unmodified registers. */
    if ((pick & ~as->modset))
      pick &= ~as->modset;
    r = rset_pickbot(pick);  /* Reduce conflicts with inverse allocation. */
  } else {
    r = ra_evict(as, allow);
  }
  RA_DBGX((as, "allock    $x $r", k, r));
  ra_setkref(as, r, k);
  rset_clear(as->freeset, r);
  ra_noweak(as, r);
  return r;
}

/* Allocate a specific register for a constant. */
static void ra_allockreg(ASMState *as, intptr_t k, Reg r)
{
  Reg kr = ra_allock(as, k, RID2RSET(r));
  if (kr != r) {
    IRIns irdummy;
    irdummy.t.irt = IRT_INT;
    ra_scratch(as, RID2RSET(r));
    emit_movrr(as, &irdummy, r, kr);
  }
}
#else
#define ra_allockreg(as, k, r)                emit_loadi(as, (r), (k))
#endif

/* Allocate a register for ref from the allowed set of registers.
** Note: this function assumes the ref does NOT have a register yet!
** Picks an optimal register, sets the cost and marks the register as non-free.
*/
static Reg ra_allocref(ASMState *as, IRRef ref, RegSet allow)
{
  IRIns *ir = IR(ref);
  RegSet pick = as->freeset & allow;
  Reg r;
  lj_assertA(ra_noreg(ir->r),
             "IR %04d already has reg %d", ref - REF_BIAS, ir->r);
  if (pick) {
    /* First check register hint from propagation or PHI. */
    if (ra_hashint(ir->r)) {
      r = ra_gethint(ir->r);
      if (rset_test(pick, r))  /* Use hint register if possible. */
        goto found;
      /* Rematerialization is cheaper than missing a hint. */
      if (rset_test(allow, r) && emit_canremat(regcost_ref(as->cost[r]))) {
        ra_rematk(as, regcost_ref(as->cost[r]));
        goto found;
      }
      RA_DBGX((as, "hintmiss  $f $r", ref, r));
    }
    /* Invariants should preferably get unmodified registers. */
    if (ref < as->loopref && !irt_isphi(ir->t)) {
      if ((pick & ~as->modset))
        pick &= ~as->modset;
      r = rset_pickbot(pick);  /* Reduce conflicts with inverse allocation. */
    } else {
      /* We've got plenty of regs, so get callee-save regs if possible. */
      if (RID_NUM_GPR > 8 && (pick & ~RSET_SCRATCH))
        pick &= ~RSET_SCRATCH;
      r = rset_picktop(pick);
    }
  } else {
    r = ra_evict(as, allow);
  }
found:
  RA_DBGX((as, "alloc     $f $r", ref, r));
  ir->r = (uint8_t)r;
  rset_clear(as->freeset, r);
  ra_noweak(as, r);
  as->cost[r] = REGCOST_REF_T(ref, irt_t(ir->t));
  return r;
}

/* Allocate a register on-demand. */
static Reg ra_alloc1(ASMState *as, IRRef ref, RegSet allow)
{
  Reg r = IR(ref)->r;
  /* Note: allow is ignored if the register is already allocated. */
  if (ra_noreg(r)) r = ra_allocref(as, ref, allow);
  ra_noweak(as, r);
  return r;
}

/* Add a register rename to the IR. */
static void ra_addrename(ASMState *as, Reg down, IRRef ref, SnapNo snapno)
{
  IRRef ren;
  lj_ir_set(as->J, IRT(IR_RENAME, IRT_NIL), ref, snapno);
  ren = tref_ref(lj_ir_emit(as->J));
  as->J->cur.ir[ren].r = (uint8_t)down;
  as->J->cur.ir[ren].s = SPS_NONE;
}

/* Rename register allocation and emit move. */
static void ra_rename(ASMState *as, Reg down, Reg up)
{
  IRRef ref = regcost_ref(as->cost[up] = as->cost[down]);
  IRIns *ir = IR(ref);
  ir->r = (uint8_t)up;
  as->cost[down] = 0;
  lj_assertA((down < RID_MAX_GPR) == (up < RID_MAX_GPR),
             "rename between GPR/FPR %d and %d", down, up);
  lj_assertA(!rset_test(as->freeset, down), "rename from free reg %d", down);
  lj_assertA(rset_test(as->freeset, up), "rename to non-free reg %d", up);
  ra_free(as, down);  /* 'down' is free ... */
  ra_modified(as, down);
  rset_clear(as->freeset, up);  /* ... and 'up' is now allocated. */
  ra_noweak(as, up);
  RA_DBGX((as, "rename    $f $r $r", regcost_ref(as->cost[up]), down, up));
  emit_movrr(as, ir, down, up);  /* Backwards codegen needs inverse move. */
  if (!ra_hasspill(IR(ref)->s)) {  /* Add the rename to the IR. */
    /*
    ** The rename is effective at the subsequent (already emitted) exit
    ** branch. This is for the current snapshot (as->snapno). Except if we
    ** haven't yet allocated any refs for the snapshot (as->snapalloc == 1),
    ** then it belongs to the next snapshot.
    ** See also the discussion at asm_snap_checkrename().
    */
    ra_addrename(as, down, ref, as->snapno + as->snapalloc);
  }
}

/* Pick a destination register (marked as free).
** Caveat: allow is ignored if there's already a destination register.
** Use ra_destreg() to get a specific register.
*/
static Reg ra_dest(ASMState *as, IRIns *ir, RegSet allow)
{
  Reg dest = ir->r;
  if (ra_hasreg(dest)) {
    ra_free(as, dest);
    ra_modified(as, dest);
  } else {
    if (ra_hashint(dest) && rset_test((as->freeset&allow), ra_gethint(dest))) {
      dest = ra_gethint(dest);
      ra_modified(as, dest);
      RA_DBGX((as, "dest           $r", dest));
    } else {
      dest = ra_scratch(as, allow);
    }
    ir->r = dest;
  }
  if (LJ_UNLIKELY(ra_hasspill(ir->s))) ra_save(as, ir, dest);
  return dest;
}

/* Force a specific destination register (marked as free). */
static void ra_destreg(ASMState *as, IRIns *ir, Reg r)
{
  Reg dest = ra_dest(as, ir, RID2RSET(r));
  if (dest != r) {
    lj_assertA(rset_test(as->freeset, r), "dest reg %d is not free", r);
    ra_modified(as, r);
    emit_movrr(as, ir, dest, r);
  }
}

#if LJ_TARGET_X86ORX64
/* Propagate dest register to left reference. Emit moves as needed.
** This is a required fixup step for all 2-operand machine instructions.
*/
static void ra_left(ASMState *as, Reg dest, IRRef lref)
{
  IRIns *ir = IR(lref);
  Reg left = ir->r;
  if (ra_noreg(left)) {
    if (irref_isk(lref)) {
      if (ir->o == IR_KNUM) {
        /* FP remat needs a load except for +0. Still better than eviction. */
        if (tvispzero(ir_knum(ir)) || !(as->freeset & RSET_FPR)) {
          emit_loadk64(as, dest, ir);
          return;
        }
#if LJ_64
      } else if (ir->o == IR_KINT64) {
        emit_loadk64(as, dest, ir);
        return;
#if LJ_GC64
      } else if (ir->o == IR_KGC || ir->o == IR_KPTR || ir->o == IR_KKPTR) {
        emit_loadk64(as, dest, ir);
        return;
#endif
#endif
      } else if (ir->o != IR_KPRI) {
        lj_assertA(ir->o == IR_KINT || ir->o == IR_KGC ||
                   ir->o == IR_KPTR || ir->o == IR_KKPTR || ir->o == IR_KNULL,
                   "K%03d has bad IR op %d", REF_BIAS - lref, ir->o);
        emit_loadi(as, dest, ir->i);
        return;
      }
    }
    if (!ra_hashint(left) && !iscrossref(as, lref))
      ra_sethint(ir->r, dest);  /* Propagate register hint. */
    left = ra_allocref(as, lref, dest < RID_MAX_GPR ? RSET_GPR : RSET_FPR);
  }
  ra_noweak(as, left);
  /* Move needed for true 3-operand instruction: y=a+b ==> y=a; y+=b. */
  if (dest != left) {
    /* Use register renaming if dest is the PHI reg. */
    if (irt_isphi(ir->t) && as->phireg[dest] == lref) {
      ra_modified(as, left);
      ra_rename(as, left, dest);
    } else {
      emit_movrr(as, ir, dest, left);
    }
  }
}
#else
/* Similar to ra_left, except we override any hints. */
static void ra_leftov(ASMState *as, Reg dest, IRRef lref)
{
  IRIns *ir = IR(lref);
  Reg left = ir->r;
  if (ra_noreg(left)) {
    ra_sethint(ir->r, dest);  /* Propagate register hint. */
    left = ra_allocref(as, lref,
                       (LJ_SOFTFP || dest < RID_MAX_GPR) ? RSET_GPR : RSET_FPR);
  }
  ra_noweak(as, left);
  if (dest != left) {
    /* Use register renaming if dest is the PHI reg. */
    if (irt_isphi(ir->t) && as->phireg[dest] == lref) {
      ra_modified(as, left);
      ra_rename(as, left, dest);
    } else {
      emit_movrr(as, ir, dest, left);
    }
  }
}
#endif

#if !LJ_64
/* Force a RID_RETLO/RID_RETHI destination register pair (marked as free). */
static void ra_destpair(ASMState *as, IRIns *ir)
{
  Reg destlo = ir->r, desthi = (ir+1)->r;
  /* First spill unrelated refs blocking the destination registers. */
  if (!rset_test(as->freeset, RID_RETLO) &&
      destlo != RID_RETLO && desthi != RID_RETLO)
    ra_restore(as, regcost_ref(as->cost[RID_RETLO]));
  if (!rset_test(as->freeset, RID_RETHI) &&
      destlo != RID_RETHI && desthi != RID_RETHI)
    ra_restore(as, regcost_ref(as->cost[RID_RETHI]));
  /* Next free the destination registers (if any). */
  if (ra_hasreg(destlo)) {
    ra_free(as, destlo);
    ra_modified(as, destlo);
  } else {
    destlo = RID_RETLO;
  }
  if (ra_hasreg(desthi)) {
    ra_free(as, desthi);
    ra_modified(as, desthi);
  } else {
    desthi = RID_RETHI;
  }
  /* Check for conflicts and shuffle the registers as needed. */
  if (destlo == RID_RETHI) {
    if (desthi == RID_RETLO) {
#if LJ_TARGET_X86
      *--as->mcp = XI_XCHGa + RID_RETHI;
#else
      emit_movrr(as, ir, RID_RETHI, RID_TMP);
      emit_movrr(as, ir, RID_RETLO, RID_RETHI);
      emit_movrr(as, ir, RID_TMP, RID_RETLO);
#endif
    } else {
      emit_movrr(as, ir, RID_RETHI, RID_RETLO);
      if (desthi != RID_RETHI) emit_movrr(as, ir, desthi, RID_RETHI);
    }
  } else if (desthi == RID_RETLO) {
    emit_movrr(as, ir, RID_RETLO, RID_RETHI);
    if (destlo != RID_RETLO) emit_movrr(as, ir, destlo, RID_RETLO);
  } else {
    if (desthi != RID_RETHI) emit_movrr(as, ir, desthi, RID_RETHI);
    if (destlo != RID_RETLO) emit_movrr(as, ir, destlo, RID_RETLO);
  }
  /* Restore spill slots (if any). */
  if (ra_hasspill((ir+1)->s)) ra_save(as, ir+1, RID_RETHI);
  if (ra_hasspill(ir->s)) ra_save(as, ir, RID_RETLO);
}
#endif

/* -- Snapshot handling --------- ----------------------------------------- */

/* Can we rematerialize a KNUM instead of forcing a spill? */
static int asm_snap_canremat(ASMState *as)
{
  Reg r;
  for (r = RID_MIN_FPR; r < RID_MAX_FPR; r++)
    if (irref_isk(regcost_ref(as->cost[r])))
      return 1;
  return 0;
}

/* Check whether a sunk store corresponds to an allocation. */
static int asm_sunk_store(ASMState *as, IRIns *ira, IRIns *irs)
{
  if (irs->s == 255) {
    if (irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
        irs->o == IR_FSTORE || irs->o == IR_XSTORE) {
      IRIns *irk = IR(irs->op1);
      if (irk->o == IR_AREF || irk->o == IR_HREFK)
        irk = IR(irk->op1);
      return (IR(irk->op1) == ira);
    }
    return 0;
  } else {
    return (ira + irs->s == irs);  /* Quick check. */
  }
}

/* Allocate register or spill slot for a ref that escapes to a snapshot. */
static void asm_snap_alloc1(ASMState *as, IRRef ref)
{
  IRIns *ir = IR(ref);
  if (!irref_isk(ref) && ir->r != RID_SUNK) {
    bloomset(as->snapfilt1, ref);
    bloomset(as->snapfilt2, hashrot(ref, ref + HASH_BIAS));
    if (ra_used(ir)) return;
    if (ir->r == RID_SINK) {
      ir->r = RID_SUNK;
#if LJ_HASFFI
      if (ir->o == IR_CNEWI) {  /* Allocate CNEWI value. */
        asm_snap_alloc1(as, ir->op2);
        if (LJ_32 && (ir+1)->o == IR_HIOP)
          asm_snap_alloc1(as, (ir+1)->op2);
      } else
#endif
      {  /* Allocate stored values for TNEW, TDUP and CNEW. */
        IRIns *irs;
        lj_assertA(ir->o == IR_TNEW || ir->o == IR_TDUP || ir->o == IR_CNEW,
                   "sink of IR %04d has bad op %d", ref - REF_BIAS, ir->o);
        for (irs = IR(as->snapref-1); irs > ir; irs--)
          if (irs->r == RID_SINK && asm_sunk_store(as, ir, irs)) {
            lj_assertA(irs->o == IR_ASTORE || irs->o == IR_HSTORE ||
                       irs->o == IR_FSTORE || irs->o == IR_XSTORE,
                       "sunk store IR %04d has bad op %d",
                       (int)(irs - as->ir) - REF_BIAS, irs->o);
            asm_snap_alloc1(as, irs->op2);
            if (LJ_32 && (irs+1)->o == IR_HIOP)
              asm_snap_alloc1(as, (irs+1)->op2);
          }
      }
    } else {
      RegSet allow;
      if (ir->o == IR_CONV && ir->op2 == IRCONV_NUM_INT) {
        IRIns *irc;
        for (irc = IR(as->curins); irc > ir; irc--)
          if ((irc->op1 == ref || irc->op2 == ref) &&
              !(irc->r == RID_SINK || irc->r == RID_SUNK))
            goto nosink;  /* Don't sink conversion if result is used. */
        asm_snap_alloc1(as, ir->op1);
        return;
      }
    nosink:
      allow = (!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR;
      if ((as->freeset & allow) ||
               (allow == RSET_FPR && asm_snap_canremat(as))) {
        /* Get a weak register if we have a free one or can rematerialize. */
        Reg r = ra_allocref(as, ref, allow);  /* Allocate a register. */
        if (!irt_isphi(ir->t))
          ra_weak(as, r);  /* But mark it as weakly referenced. */
        checkmclim(as);
        RA_DBGX((as, "snapreg   $f $r", ref, ir->r));
      } else {
        ra_spill(as, ir);  /* Otherwise force a spill slot. */
        RA_DBGX((as, "snapspill $f $s", ref, ir->s));
      }
    }
  }
}

/* Allocate refs escaping to a snapshot. */
static void asm_snap_alloc(ASMState *as, int snapno)
{
  SnapShot *snap = &as->T->snap[snapno];
  SnapEntry *map = &as->T->snapmap[snap->mapofs];
  MSize n, nent = snap->nent;
  as->snapfilt1 = as->snapfilt2 = 0;
  for (n = 0; n < nent; n++) {
    SnapEntry sn = map[n];
    IRRef ref = snap_ref(sn);
    if (!irref_isk(ref)) {
      asm_snap_alloc1(as, ref);
      if (LJ_SOFTFP && (sn & SNAP_SOFTFPNUM)) {
        lj_assertA(irt_type(IR(ref+1)->t) == IRT_SOFTFP,
                   "snap %d[%d] points to bad SOFTFP IR %04d",
                   snapno, n, ref - REF_BIAS);
        asm_snap_alloc1(as, ref+1);
      }
    }
  }
}

/* All guards for a snapshot use the same exitno. This is currently the
** same as the snapshot number. Since the exact origin of the exit cannot
** be determined, all guards for the same snapshot must exit with the same
** RegSP mapping.
** A renamed ref which has been used in a prior guard for the same snapshot
** would cause an inconsistency. The easy way out is to force a spill slot.
*/
static int asm_snap_checkrename(ASMState *as, IRRef ren)
{
  if (bloomtest(as->snapfilt1, ren) &&
      bloomtest(as->snapfilt2, hashrot(ren, ren + HASH_BIAS))) {
    IRIns *ir = IR(ren);
    ra_spill(as, ir);  /* Register renamed, so force a spill slot. */
    RA_DBGX((as, "snaprensp $f $s", ren, ir->s));
    return 1;  /* Found. */
  }
  return 0;  /* Not found. */
}

/* Prepare snapshot for next guard or throwing instruction. */
static void asm_snap_prep(ASMState *as)
{
  if (as->snapalloc) {
    /* Alloc on first invocation for each snapshot. */
    as->snapalloc = 0;
    asm_snap_alloc(as, as->snapno);
    as->snaprename = as->T->nins;
  } else {
    /* Check any renames above the highwater mark. */
    for (; as->snaprename < as->T->nins; as->snaprename++) {
      IRIns *ir = &as->T->ir[as->snaprename];
      if (asm_snap_checkrename(as, ir->op1))
        ir->op2 = REF_BIAS-1;  /* Kill rename. */
    }
  }
}

/* Move to previous snapshot when we cross the current snapshot ref. */
static void asm_snap_prev(ASMState *as)
{
  if (as->curins < as->snapref) {
    ptrdiff_t ofs = as->mctoporig - as->mcp;
    if (ofs >= 0x10000) lj_trace_err(as->J, LJ_TRERR_MCODEOV);
    do {
      if (as->snapno == 0) return;
      as->snapno--;
      as->snapref = as->T->snap[as->snapno].ref;
      as->T->snap[as->snapno].mcofs = ofs;  /* Remember mcode offset. */
    } while (as->curins < as->snapref);  /* May have no ins inbetween. */
    as->snapalloc = 1;
  }
}

/* Fixup snapshot mcode offsetst. */
static void asm_snap_fixup_mcofs(ASMState *as)
{
  uint32_t sz = (uint32_t)(as->mctoporig - as->mcp);
  SnapShot *snap = as->T->snap;
  SnapNo i;
  for (i = as->T->nsnap-1; i > 0; i--) {
    /* Compute offset from mcode start and store in correct snapshot. */
    snap[i].mcofs = (uint16_t)(sz - snap[i-1].mcofs);
  }
  snap[0].mcofs = 0;
}

/* -- Miscellaneous helpers ----------------------------------------------- */

/* Calculate stack adjustment. */
static int32_t asm_stack_adjust(ASMState *as)
{
  if (as->evenspill <= SPS_FIXED)
    return 0;
  return sps_scale(sps_align(as->evenspill));
}

/* Must match with hash*() in lj_tab.c. */
static uint32_t ir_khash(ASMState *as, IRIns *ir)
{
  uint32_t lo, hi;
  UNUSED(as);
  if (irt_isstr(ir->t)) {
    return ir_kstr(ir)->hash;
  } else if (irt_isnum(ir->t)) {
    lo = ir_knum(ir)->u32.lo;
    hi = ir_knum(ir)->u32.hi << 1;
  } else if (irt_ispri(ir->t)) {
    lj_assertA(!irt_isnil(ir->t), "hash of nil key");
    return irt_type(ir->t)-IRT_FALSE;
  } else {
    lj_assertA(irt_isgcv(ir->t), "hash of bad IR type %d", irt_type(ir->t));
    lo = u32ptr(ir_kgc(ir));
#if LJ_GC64
    hi = (uint32_t)(u64ptr(ir_kgc(ir)) >> 32) | (irt_toitype(ir->t) << 15);
#else
    hi = lo + HASH_BIAS;
#endif
  }
  return hashrot(lo, hi);
}

/* -- Allocations --------------------------------------------------------- */

static void asm_gencall(ASMState *as, const CCallInfo *ci, IRRef *args);
static void asm_setupresult(ASMState *as, IRIns *ir, const CCallInfo *ci);

static void asm_snew(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_str_new];
  IRRef args[3];
  asm_snap_prep(as);
  args[0] = ASMREF_L;  /* lua_State *L    */
  args[1] = ir->op1;   /* const char *str */
  args[2] = ir->op2;   /* size_t len      */
  as->gcsteps++;
  asm_setupresult(as, ir, ci);  /* GCstr * */
  asm_gencall(as, ci, args);
}

static void asm_tnew(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_tab_new1];
  IRRef args[2];
  asm_snap_prep(as);
  args[0] = ASMREF_L;     /* lua_State *L    */
  args[1] = ASMREF_TMP1;  /* uint32_t ahsize */
  as->gcsteps++;
  asm_setupresult(as, ir, ci);  /* GCtab * */
  asm_gencall(as, ci, args);
  ra_allockreg(as, ir->op1 | (ir->op2 << 24), ra_releasetmp(as, ASMREF_TMP1));
}

static void asm_tdup(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_tab_dup];
  IRRef args[2];
  asm_snap_prep(as);
  args[0] = ASMREF_L;  /* lua_State *L    */
  args[1] = ir->op1;   /* const GCtab *kt */
  as->gcsteps++;
  asm_setupresult(as, ir, ci);  /* GCtab * */
  asm_gencall(as, ci, args);
}

static void asm_gc_check(ASMState *as);

/* Explicit GC step. */
static void asm_gcstep(ASMState *as, IRIns *ir)
{
  IRIns *ira;
  for (ira = IR(as->stopins+1); ira < ir; ira++)
    if ((ira->o == IR_TNEW || ira->o == IR_TDUP ||
         (LJ_HASFFI && (ira->o == IR_CNEW || ira->o == IR_CNEWI))) &&
        ra_used(ira))
      as->gcsteps++;
  if (as->gcsteps)
    asm_gc_check(as);
  as->gcsteps = 0x80000000;  /* Prevent implicit GC check further up. */
}

/* -- Buffer operations --------------------------------------------------- */

static void asm_tvptr(ASMState *as, Reg dest, IRRef ref);

static void asm_bufhdr(ASMState *as, IRIns *ir)
{
  Reg sb = ra_dest(as, ir, RSET_GPR);
  if ((ir->op2 & IRBUFHDR_APPEND)) {
    /* Rematerialize const buffer pointer instead of likely spill. */
    IRIns *irp = IR(ir->op1);
    if (!(ra_hasreg(irp->r) || irp == ir-1 ||
          (irp == ir-2 && !ra_used(ir-1)))) {
      while (!(irp->o == IR_BUFHDR && !(irp->op2 & IRBUFHDR_APPEND)))
        irp = IR(irp->op1);
      if (irref_isk(irp->op1)) {
        ra_weak(as, ra_allocref(as, ir->op1, RSET_GPR));
        ir = irp;
      }
    }
  } else {
    Reg tmp = ra_scratch(as, rset_exclude(RSET_GPR, sb));
    /* Passing ir isn't strictly correct, but it's an IRT_PGC, too. */
    emit_storeofs(as, ir, tmp, sb, offsetof(SBuf, p));
    emit_loadofs(as, ir, tmp, sb, offsetof(SBuf, b));
  }
#if LJ_TARGET_X86ORX64
  ra_left(as, sb, ir->op1);
#else
  ra_leftov(as, sb, ir->op1);
#endif
}

static void asm_bufput(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_buf_putstr];
  IRRef args[3];
  IRIns *irs;
  int kchar = -129;
  args[0] = ir->op1;  /* SBuf * */
  args[1] = ir->op2;  /* GCstr * */
  irs = IR(ir->op2);
  lj_assertA(irt_isstr(irs->t),
             "BUFPUT of non-string IR %04d", ir->op2 - REF_BIAS);
  if (irs->o == IR_KGC) {
    GCstr *s = ir_kstr(irs);
    if (s->len == 1) {  /* Optimize put of single-char string constant. */
      kchar = (int8_t)strdata(s)[0];  /* Signed! */
      args[1] = ASMREF_TMP1;  /* int, truncated to char */
      ci = &lj_ir_callinfo[IRCALL_lj_buf_putchar];
    }
  } else if (mayfuse(as, ir->op2) && ra_noreg(irs->r)) {
    if (irs->o == IR_TOSTR) {  /* Fuse number to string conversions. */
      if (irs->op2 == IRTOSTR_NUM) {
        args[1] = ASMREF_TMP1;  /* TValue * */
        ci = &lj_ir_callinfo[IRCALL_lj_strfmt_putnum];
      } else {
        lj_assertA(irt_isinteger(IR(irs->op1)->t),
                   "TOSTR of non-numeric IR %04d", irs->op1);
        args[1] = irs->op1;  /* int */
        if (irs->op2 == IRTOSTR_INT)
          ci = &lj_ir_callinfo[IRCALL_lj_strfmt_putint];
        else
          ci = &lj_ir_callinfo[IRCALL_lj_buf_putchar];
      }
    } else if (irs->o == IR_SNEW) {  /* Fuse string allocation. */
      args[1] = irs->op1;  /* const void * */
      args[2] = irs->op2;  /* MSize */
      ci = &lj_ir_callinfo[IRCALL_lj_buf_putmem];
    }
  }
  asm_setupresult(as, ir, ci);  /* SBuf * */
  asm_gencall(as, ci, args);
  if (args[1] == ASMREF_TMP1) {
    Reg tmp = ra_releasetmp(as, ASMREF_TMP1);
    if (kchar == -129)
      asm_tvptr(as, tmp, irs->op1);
    else
      ra_allockreg(as, kchar, tmp);
  }
}

static void asm_bufstr(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_buf_tostr];
  IRRef args[1];
  args[0] = ir->op1;  /* SBuf *sb */
  as->gcsteps++;
  asm_setupresult(as, ir, ci);  /* GCstr * */
  asm_gencall(as, ci, args);
}

/* -- Type conversions ---------------------------------------------------- */

static void asm_tostr(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci;
  IRRef args[2];
  asm_snap_prep(as);
  args[0] = ASMREF_L;
  as->gcsteps++;
  if (ir->op2 == IRTOSTR_NUM) {
    args[1] = ASMREF_TMP1;  /* cTValue * */
    ci = &lj_ir_callinfo[IRCALL_lj_strfmt_num];
  } else {
    args[1] = ir->op1;  /* int32_t k */
    if (ir->op2 == IRTOSTR_INT)
      ci = &lj_ir_callinfo[IRCALL_lj_strfmt_int];
    else
      ci = &lj_ir_callinfo[IRCALL_lj_strfmt_char];
  }
  asm_setupresult(as, ir, ci);  /* GCstr * */
  asm_gencall(as, ci, args);
  if (ir->op2 == IRTOSTR_NUM)
    asm_tvptr(as, ra_releasetmp(as, ASMREF_TMP1), ir->op1);
}

#if LJ_32 && LJ_HASFFI && !LJ_SOFTFP && !LJ_TARGET_X86
static void asm_conv64(ASMState *as, IRIns *ir)
{
  IRType st = (IRType)((ir-1)->op2 & IRCONV_SRCMASK);
  IRType dt = (((ir-1)->op2 & IRCONV_DSTMASK) >> IRCONV_DSH);
  IRCallID id;
  IRRef args[2];
  lj_assertA((ir-1)->o == IR_CONV && ir->o == IR_HIOP,
             "not a CONV/HIOP pair at IR %04d", (int)(ir - as->ir) - REF_BIAS);
  args[LJ_BE] = (ir-1)->op1;
  args[LJ_LE] = ir->op1;
  if (st == IRT_NUM || st == IRT_FLOAT) {
    id = IRCALL_fp64_d2l + ((st == IRT_FLOAT) ? 2 : 0) + (dt - IRT_I64);
    ir--;
  } else {
    id = IRCALL_fp64_l2d + ((dt == IRT_FLOAT) ? 2 : 0) + (st - IRT_I64);
  }
  {
#if LJ_TARGET_ARM && !LJ_ABI_SOFTFP
    CCallInfo cim = lj_ir_callinfo[id], *ci = &cim;
    cim.flags |= CCI_VARARG;  /* These calls don't use the hard-float ABI! */
#else
    const CCallInfo *ci = &lj_ir_callinfo[id];
#endif
    asm_setupresult(as, ir, ci);
    asm_gencall(as, ci, args);
  }
}
#endif

/* -- Memory references --------------------------------------------------- */

static void asm_newref(ASMState *as, IRIns *ir)
{
  const CCallInfo *ci = &lj_ir_callinfo[IRCALL_lj_tab_newkey];
  IRRef args[3];
  if (ir->r == RID_SINK)
    return;
  asm_snap_prep(as);
  args[0] = ASMREF_L;     /* lua_State *L */
  args[1] = ir->op1;      /* GCtab *t     */
  args[2] = ASMREF_TMP1;  /* cTValue *key */
  asm_setupresult(as, ir, ci);  /* TValue * */
  asm_gencall(as, ci, args);
  asm_tvptr(as, ra_releasetmp(as, ASMREF_TMP1), ir->op2);
}

static void asm_lref(ASMState *as, IRIns *ir)
{
  Reg r = ra_dest(as, ir, RSET_GPR);
#if LJ_TARGET_X86ORX64
  ra_left(as, r, ASMREF_L);
#else
  ra_leftov(as, r, ASMREF_L);
#endif
}

/* -- Calls --------------------------------------------------------------- */

/* Collect arguments from CALL* and CARG instructions. */
static void asm_collectargs(ASMState *as, IRIns *ir,
                            const CCallInfo *ci, IRRef *args)
{
  uint32_t n = CCI_XNARGS(ci);
  /* Account for split args. */
  lj_assertA(n <= CCI_NARGS_MAX*2, "too many args %d to collect", n);
  if ((ci->flags & CCI_L)) { *args++ = ASMREF_L; n--; }
  while (n-- > 1) {
    ir = IR(ir->op1);
    lj_assertA(ir->o == IR_CARG, "malformed CALL arg tree");
    args[n] = ir->op2 == REF_NIL ? 0 : ir->op2;
  }
  args[0] = ir->op1 == REF_NIL ? 0 : ir->op1;
  lj_assertA(IR(ir->op1)->o != IR_CARG, "malformed CALL arg tree");
}

/* Reconstruct CCallInfo flags for CALLX*. */
static uint32_t asm_callx_flags(ASMState *as, IRIns *ir)
{
  uint32_t nargs = 0;
  if (ir->op1 != REF_NIL) {  /* Count number of arguments first. */
    IRIns *ira = IR(ir->op1);
    nargs++;
    while (ira->o == IR_CARG) { nargs++; ira = IR(ira->op1); }
  }
#if LJ_HASFFI
  if (IR(ir->op2)->o == IR_CARG) {  /* Copy calling convention info. */
    CTypeID id = (CTypeID)IR(IR(ir->op2)->op2)->i;
    CType *ct = ctype_get(ctype_ctsG(J2G(as->J)), id);
    nargs |= ((ct->info & CTF_VARARG) ? CCI_VARARG : 0);
#if LJ_TARGET_X86
    nargs |= (ctype_cconv(ct->info) << CCI_CC_SHIFT);
#endif
  }
#endif
  return (nargs | (ir->t.irt << CCI_OTSHIFT));
}

static void asm_callid(ASMState *as, IRIns *ir, IRCallID id)
{
  const CCallInfo *ci = &lj_ir_callinfo[id];
  IRRef args[2];
  args[0] = ir->op1;
  args[1] = ir->op2;
  asm_setupresult(as, ir, ci);
  asm_gencall(as, ci, args);
}

static void asm_call(ASMState *as, IRIns *ir)
{
  IRRef args[CCI_NARGS_MAX];
  const CCallInfo *ci = &lj_ir_callinfo[ir->op2];
  asm_collectargs(as, ir, ci, args);
  asm_setupresult(as, ir, ci);
  asm_gencall(as, ci, args);
}

/* -- PHI and loop handling ----------------------------------------------- */

/* Break a PHI cycle by renaming to a free register (evict if needed). */
static void asm_phi_break(ASMState *as, RegSet blocked, RegSet blockedby,
                          RegSet allow)
{
  RegSet candidates = blocked & allow;
  if (candidates) {  /* If this register file has candidates. */
    /* Note: the set for ra_pick cannot be empty, since each register file
    ** has some registers never allocated to PHIs.
    */
    Reg down, up = ra_pick(as, ~blocked & allow);  /* Get a free register. */
    if (candidates & ~blockedby)  /* Optimize shifts, else it's a cycle. */
      candidates = candidates & ~blockedby;
    down = rset_picktop(candidates);  /* Pick candidate PHI register. */
    ra_rename(as, down, up);  /* And rename it to the free register. */
  }
}

/* PHI register shuffling.
**
** The allocator tries hard to preserve PHI register assignments across
** the loop body. Most of the time this loop does nothing, since there
** are no register mismatches.
**
** If a register mismatch is detected and ...
** - the register is currently free: rename it.
** - the register is blocked by an invariant: restore/remat and rename it.
** - Otherwise the register is used by another PHI, so mark it as blocked.
**
** The renames are order-sensitive, so just retry the loop if a register
** is marked as blocked, but has been freed in the meantime. A cycle is
** detected if all of the blocked registers are allocated. To break the
** cycle rename one of them to a free register and retry.
**
** Note that PHI spill slots are kept in sync and don't need to be shuffled.
*/
static void asm_phi_shuffle(ASMState *as)
{
  RegSet work;

  /* Find and resolve PHI register mismatches. */
  for (;;) {
    RegSet blocked = RSET_EMPTY;
    RegSet blockedby = RSET_EMPTY;
    RegSet phiset = as->phiset;
    while (phiset) {  /* Check all left PHI operand registers. */
      Reg r = rset_pickbot(phiset);
      IRIns *irl = IR(as->phireg[r]);
      Reg left = irl->r;
      if (r != left) {  /* Mismatch? */
        if (!rset_test(as->freeset, r)) {  /* PHI register blocked? */
          IRRef ref = regcost_ref(as->cost[r]);
          /* Blocked by other PHI (w/reg)? */
          if (!ra_iskref(ref) && irt_ismarked(IR(ref)->t)) {
            rset_set(blocked, r);
            if (ra_hasreg(left))
              rset_set(blockedby, left);
            left = RID_NONE;
          } else {  /* Otherwise grab register from invariant. */
            ra_restore(as, ref);
            checkmclim(as);
          }
        }
        if (ra_hasreg(left)) {
          ra_rename(as, left, r);
          checkmclim(as);
        }
      }
      rset_clear(phiset, r);
    }
    if (!blocked) break;  /* Finished. */
    if (!(as->freeset & blocked)) {  /* Break cycles if none are free. */
      asm_phi_break(as, blocked, blockedby, RSET_GPR);
      if (!LJ_SOFTFP) asm_phi_break(as, blocked, blockedby, RSET_FPR);
      checkmclim(as);
    }  /* Else retry some more renames. */
  }

  /* Restore/remat invariants whose registers are modified inside the loop. */
#if !LJ_SOFTFP
  work = as->modset & ~(as->freeset | as->phiset) & RSET_FPR;
  while (work) {
    Reg r = rset_pickbot(work);
    ra_restore(as, regcost_ref(as->cost[r]));
    rset_clear(work, r);
    checkmclim(as);
  }
#endif
  work = as->modset & ~(as->freeset | as->phiset);
  while (work) {
    Reg r = rset_pickbot(work);
    ra_restore(as, regcost_ref(as->cost[r]));
    rset_clear(work, r);
    checkmclim(as);
  }

  /* Allocate and save all unsaved PHI regs and clear marks. */
  work = as->phiset;
  while (work) {
    Reg r = rset_picktop(work);
    IRRef lref = as->phireg[r];
    IRIns *ir = IR(lref);
    if (ra_hasspill(ir->s)) {  /* Left PHI gained a spill slot? */
      irt_clearmark(ir->t);  /* Handled here, so clear marker now. */
      ra_alloc1(as, lref, RID2RSET(r));
      ra_save(as, ir, r);  /* Save to spill slot inside the loop. */
      checkmclim(as);
    }
    rset_clear(work, r);
  }
}

/* Copy unsynced left/right PHI spill slots. Rarely needed. */
static void asm_phi_copyspill(ASMState *as)
{
  int need = 0;
  IRIns *ir;
  for (ir = IR(as->orignins-1); ir->o == IR_PHI; ir--)
    if (ra_hasspill(ir->s) && ra_hasspill(IR(ir->op1)->s))
      need |= irt_isfp(ir->t) ? 2 : 1;  /* Unsynced spill slot? */
  if ((need & 1)) {  /* Copy integer spill slots. */
#if !LJ_TARGET_X86ORX64
    Reg r = RID_TMP;
#else
    Reg r = RID_RET;
    if ((as->freeset & RSET_GPR))
      r = rset_pickbot((as->freeset & RSET_GPR));
    else
      emit_spload(as, IR(regcost_ref(as->cost[r])), r, SPOFS_TMP);
#endif
    for (ir = IR(as->orignins-1); ir->o == IR_PHI; ir--) {
      if (ra_hasspill(ir->s)) {
        IRIns *irl = IR(ir->op1);
        if (ra_hasspill(irl->s) && !irt_isfp(ir->t)) {
          emit_spstore(as, irl, r, sps_scale(irl->s));
          emit_spload(as, ir, r, sps_scale(ir->s));
          checkmclim(as);
        }
      }
    }
#if LJ_TARGET_X86ORX64
    if (!rset_test(as->freeset, r))
      emit_spstore(as, IR(regcost_ref(as->cost[r])), r, SPOFS_TMP);
#endif
  }
#if !LJ_SOFTFP
  if ((need & 2)) {  /* Copy FP spill slots. */
#if LJ_TARGET_X86
    Reg r = RID_XMM0;
#else
    Reg r = RID_FPRET;
#endif
    if ((as->freeset & RSET_FPR))
      r = rset_pickbot((as->freeset & RSET_FPR));
    if (!rset_test(as->freeset, r))
      emit_spload(as, IR(regcost_ref(as->cost[r])), r, SPOFS_TMP);
    for (ir = IR(as->orignins-1); ir->o == IR_PHI; ir--) {
      if (ra_hasspill(ir->s)) {
        IRIns *irl = IR(ir->op1);
        if (ra_hasspill(irl->s) && irt_isfp(ir->t)) {
          emit_spstore(as, irl, r, sps_scale(irl->s));
          emit_spload(as, ir, r, sps_scale(ir->s));
          checkmclim(as);
        }
      }
    }
    if (!rset_test(as->freeset, r))
      emit_spstore(as, IR(regcost_ref(as->cost[r])), r, SPOFS_TMP);
  }
#endif
}

/* Emit renames for left PHIs which are only spilled outside the loop. */
static void asm_phi_fixup(ASMState *as)
{
  RegSet work = as->phiset;
  while (work) {
    Reg r = rset_picktop(work);
    IRRef lref = as->phireg[r];
    IRIns *ir = IR(lref);
    if (irt_ismarked(ir->t)) {
      irt_clearmark(ir->t);
      /* Left PHI gained a spill slot before the loop? */
      if (ra_hasspill(ir->s)) {
        ra_addrename(as, r, lref, as->loopsnapno);
      }
    }
    rset_clear(work, r);
  }
}

/* Setup right PHI reference. */
static void asm_phi(ASMState *as, IRIns *ir)
{
  RegSet allow = ((!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR) &
                 ~as->phiset;
  RegSet afree = (as->freeset & allow);
  IRIns *irl = IR(ir->op1);
  IRIns *irr = IR(ir->op2);
  if (ir->r == RID_SINK)  /* Sink PHI. */
    return;
  /* Spill slot shuffling is not implemented yet (but rarely needed). */
  if (ra_hasspill(irl->s) || ra_hasspill(irr->s))
    lj_trace_err(as->J, LJ_TRERR_NYIPHI);
  /* Leave at least one register free for non-PHIs (and PHI cycle breaking). */
  if ((afree & (afree-1))) {  /* Two or more free registers? */
    Reg r;
    if (ra_noreg(irr->r)) {  /* Get a register for the right PHI. */
      r = ra_allocref(as, ir->op2, allow);
    } else {  /* Duplicate right PHI, need a copy (rare). */
      r = ra_scratch(as, allow);
      emit_movrr(as, irr, r, irr->r);
    }
    ir->r = (uint8_t)r;
    rset_set(as->phiset, r);
    as->phireg[r] = (IRRef1)ir->op1;
    irt_setmark(irl->t);  /* Marks left PHIs _with_ register. */
    if (ra_noreg(irl->r))
      ra_sethint(irl->r, r); /* Set register hint for left PHI. */
  } else {  /* Otherwise allocate a spill slot. */
    /* This is overly restrictive, but it triggers only on synthetic code. */
    if (ra_hasreg(irl->r) || ra_hasreg(irr->r))
      lj_trace_err(as->J, LJ_TRERR_NYIPHI);
    ra_spill(as, ir);
    irr->s = ir->s;  /* Set right PHI spill slot. Sync left slot later. */
  }
}

static void asm_loop_fixup(ASMState *as);

/* Middle part of a loop. */
static void asm_loop(ASMState *as)
{
  MCode *mcspill;
  /* LOOP is a guard, so the snapno is up to date. */
  as->loopsnapno = as->snapno;
  if (as->gcsteps)
    asm_gc_check(as);
  /* LOOP marks the transition from the variant to the invariant part. */
  as->flagmcp = as->invmcp = NULL;
  as->sectref = 0;
  if (!neverfuse(as)) as->fuseref = 0;
  asm_phi_shuffle(as);
  mcspill = as->mcp;
  asm_phi_copyspill(as);
  asm_loop_fixup(as);
  as->mcloop = as->mcp;
  RA_DBGX((as, "===== LOOP ====="));
  if (!as->realign) RA_DBG_FLUSH();
  if (as->mcp != mcspill)
    emit_jmp(as, mcspill);
}

/* -- Target-specific assembler ------------------------------------------- */

#if LJ_TARGET_X86ORX64
#include "lj_asm_x86.h"
#elif LJ_TARGET_ARM
#include "lj_asm_arm.h"
#elif LJ_TARGET_ARM64
#include "lj_asm_arm64.h"
#elif LJ_TARGET_PPC
#include "lj_asm_ppc.h"
#elif LJ_TARGET_MIPS
#include "lj_asm_mips.h"
#else
#error "Missing assembler for target CPU"
#endif

/* -- Common instruction helpers ------------------------------------------ */

#if !LJ_SOFTFP32
#if !LJ_TARGET_X86ORX64
#define asm_ldexp(as, ir)        asm_callid(as, ir, IRCALL_ldexp)
#endif

static void asm_pow(ASMState *as, IRIns *ir)
{
#if LJ_64 && LJ_HASFFI
  if (!irt_isnum(ir->t))
    asm_callid(as, ir, irt_isi64(ir->t) ? IRCALL_lj_carith_powi64 :
                                          IRCALL_lj_carith_powu64);
  else
#endif
  asm_callid(as, ir, IRCALL_pow);
}

static void asm_div(ASMState *as, IRIns *ir)
{
#if LJ_64 && LJ_HASFFI
  if (!irt_isnum(ir->t))
    asm_callid(as, ir, irt_isi64(ir->t) ? IRCALL_lj_carith_divi64 :
                                          IRCALL_lj_carith_divu64);
  else
#endif
    asm_fpdiv(as, ir);
}
#endif

static void asm_mod(ASMState *as, IRIns *ir)
{
#if LJ_64 && LJ_HASFFI
  if (!irt_isint(ir->t))
    asm_callid(as, ir, irt_isi64(ir->t) ? IRCALL_lj_carith_modi64 :
                                          IRCALL_lj_carith_modu64);
  else
#endif
    asm_callid(as, ir, IRCALL_lj_vm_modi);
}

static void asm_fuseequal(ASMState *as, IRIns *ir)
{
  /* Fuse HREF + EQ/NE. */
  if ((ir-1)->o == IR_HREF && ir->op1 == as->curins-1) {
    as->curins--;
    asm_href(as, ir-1, (IROp)ir->o);
  } else {
    asm_equal(as, ir);
  }
}

/* -- Instruction dispatch ------------------------------------------------ */

/* Assemble a single instruction. */
static void asm_ir(ASMState *as, IRIns *ir)
{
  switch ((IROp)ir->o) {
  /* Miscellaneous ops. */
  case IR_LOOP: asm_loop(as); break;
  case IR_NOP: case IR_XBAR:
    lj_assertA(!ra_used(ir),
               "IR %04d not unused", (int)(ir - as->ir) - REF_BIAS);
    break;
  case IR_USE:
    ra_alloc1(as, ir->op1, irt_isfp(ir->t) ? RSET_FPR : RSET_GPR); break;
  case IR_PHI: asm_phi(as, ir); break;
  case IR_HIOP: asm_hiop(as, ir); break;
  case IR_GCSTEP: asm_gcstep(as, ir); break;
  case IR_PROF: asm_prof(as, ir); break;

  /* Guarded assertions. */
  case IR_LT: case IR_GE: case IR_LE: case IR_GT:
  case IR_ULT: case IR_UGE: case IR_ULE: case IR_UGT:
  case IR_ABC:
    asm_comp(as, ir);
    break;
  case IR_EQ: case IR_NE: asm_fuseequal(as, ir); break;

  case IR_RETF: asm_retf(as, ir); break;

  /* Bit ops. */
  case IR_BNOT: asm_bnot(as, ir); break;
  case IR_BSWAP: asm_bswap(as, ir); break;
  case IR_BAND: asm_band(as, ir); break;
  case IR_BOR: asm_bor(as, ir); break;
  case IR_BXOR: asm_bxor(as, ir); break;
  case IR_BSHL: asm_bshl(as, ir); break;
  case IR_BSHR: asm_bshr(as, ir); break;
  case IR_BSAR: asm_bsar(as, ir); break;
  case IR_BROL: asm_brol(as, ir); break;
  case IR_BROR: asm_bror(as, ir); break;

  /* Arithmetic ops. */
  case IR_ADD: asm_add(as, ir); break;
  case IR_SUB: asm_sub(as, ir); break;
  case IR_MUL: asm_mul(as, ir); break;
  case IR_MOD: asm_mod(as, ir); break;
  case IR_NEG: asm_neg(as, ir); break;
#if LJ_SOFTFP32
  case IR_DIV: case IR_POW: case IR_ABS:
  case IR_LDEXP: case IR_FPMATH: case IR_TOBIT:
    /* Unused for LJ_SOFTFP32. */
    lj_assertA(0, "IR %04d with unused op %d",
                  (int)(ir - as->ir) - REF_BIAS, ir->o);
    break;
#else
  case IR_DIV: asm_div(as, ir); break;
  case IR_POW: asm_pow(as, ir); break;
  case IR_ABS: asm_abs(as, ir); break;
  case IR_LDEXP: asm_ldexp(as, ir); break;
  case IR_FPMATH: asm_fpmath(as, ir); break;
  case IR_TOBIT: asm_tobit(as, ir); break;
#endif
  case IR_MIN: asm_min(as, ir); break;
  case IR_MAX: asm_max(as, ir); break;

  /* Overflow-checking arithmetic ops. */
  case IR_ADDOV: asm_addov(as, ir); break;
  case IR_SUBOV: asm_subov(as, ir); break;
  case IR_MULOV: asm_mulov(as, ir); break;

  /* Memory references. */
  case IR_AREF: asm_aref(as, ir); break;
  case IR_HREF: asm_href(as, ir, 0); break;
  case IR_HREFK: asm_hrefk(as, ir); break;
  case IR_NEWREF: asm_newref(as, ir); break;
  case IR_UREFO: case IR_UREFC: asm_uref(as, ir); break;
  case IR_FREF: asm_fref(as, ir); break;
  case IR_STRREF: asm_strref(as, ir); break;
  case IR_LREF: asm_lref(as, ir); break;

  /* Loads and stores. */
  case IR_ALOAD: case IR_HLOAD: case IR_ULOAD: case IR_VLOAD:
    asm_ahuvload(as, ir);
    break;
  case IR_FLOAD: asm_fload(as, ir); break;
  case IR_XLOAD: asm_xload(as, ir); break;
  case IR_SLOAD: asm_sload(as, ir); break;

  case IR_ASTORE: case IR_HSTORE: case IR_USTORE: asm_ahustore(as, ir); break;
  case IR_FSTORE: asm_fstore(as, ir); break;
  case IR_XSTORE: asm_xstore(as, ir); break;

  /* Allocations. */
  case IR_SNEW: case IR_XSNEW: asm_snew(as, ir); break;
  case IR_TNEW: asm_tnew(as, ir); break;
  case IR_TDUP: asm_tdup(as, ir); break;
  case IR_CNEW: case IR_CNEWI:
#if LJ_HASFFI
    asm_cnew(as, ir);
#else
    lj_assertA(0, "IR %04d with unused op %d",
                  (int)(ir - as->ir) - REF_BIAS, ir->o);
#endif
    break;

  /* Buffer operations. */
  case IR_BUFHDR: asm_bufhdr(as, ir); break;
  case IR_BUFPUT: asm_bufput(as, ir); break;
  case IR_BUFSTR: asm_bufstr(as, ir); break;

  /* Write barriers. */
  case IR_TBAR: asm_tbar(as, ir); break;
  case IR_OBAR: asm_obar(as, ir); break;

  /* Type conversions. */
  case IR_CONV: asm_conv(as, ir); break;
  case IR_TOSTR: asm_tostr(as, ir); break;
  case IR_STRTO: asm_strto(as, ir); break;

  /* Calls. */
  case IR_CALLA:
    as->gcsteps++;
    /* fallthrough */
  case IR_CALLN: case IR_CALLL: case IR_CALLS: asm_call(as, ir); break;
  case IR_CALLXS: asm_callx(as, ir); break;
  case IR_CARG: break;

  default:
    setintV(&as->J->errinfo, ir->o);
    lj_trace_err_info(as->J, LJ_TRERR_NYIIR);
    break;
  }
}

/* -- Head of trace ------------------------------------------------------- */

/* Head of a root trace. */
static void asm_head_root(ASMState *as)
{
  int32_t spadj;
  asm_head_root_base(as);
  emit_setvmstate(as, (int32_t)as->T->traceno);
  spadj = asm_stack_adjust(as);
  as->T->spadjust = (uint16_t)spadj;
  emit_spsub(as, spadj);
  /* Root traces assume a checked stack for the starting proto. */
  as->T->topslot = gcref(as->T->startpt)->pt.framesize;
}

/* Head of a side trace.
**
** The current simplistic algorithm requires that all slots inherited
** from the parent are live in a register between pass 2 and pass 3. This
** avoids the complexity of stack slot shuffling. But of course this may
** overflow the register set in some cases and cause the dreaded error:
** "NYI: register coalescing too complex". A refined algorithm is needed.
*/
static void asm_head_side(ASMState *as)
{
  IRRef1 sloadins[RID_MAX];
  RegSet allow = RSET_ALL;  /* Inverse of all coalesced registers. */
  RegSet live = RSET_EMPTY;  /* Live parent registers. */
  RegSet pallow = RSET_GPR;  /* Registers needed by the parent stack check. */
  Reg pbase;
  IRIns *irp = &as->parent->ir[REF_BASE];  /* Parent base. */
  int32_t spadj, spdelta;
  int pass2 = 0;
  int pass3 = 0;
  IRRef i;

  if (as->snapno && as->topslot > as->parent->topslot) {
    /* Force snap #0 alloc to prevent register overwrite in stack check. */
    asm_snap_alloc(as, 0);
  }
  pbase = asm_head_side_base(as, irp);
  if (pbase != RID_NONE) {
    rset_clear(allow, pbase);
    rset_clear(pallow, pbase);
  }

  /* Scan all parent SLOADs and collect register dependencies. */
  for (i = as->stopins; i > REF_BASE; i--) {
    IRIns *ir = IR(i);
    RegSP rs;
    lj_assertA((ir->o == IR_SLOAD && (ir->op2 & IRSLOAD_PARENT)) ||
               (LJ_SOFTFP && ir->o == IR_HIOP) || ir->o == IR_PVAL,
               "IR %04d has bad parent op %d",
               (int)(ir - as->ir) - REF_BIAS, ir->o);
    rs = as->parentmap[i - REF_FIRST];
    if (ra_hasreg(ir->r)) {
      rset_clear(allow, ir->r);
      if (ra_hasspill(ir->s)) {
        ra_save(as, ir, ir->r);
        checkmclim(as);
      }
    } else if (ra_hasspill(ir->s)) {
      irt_setmark(ir->t);
      pass2 = 1;
    }
    if (ir->r == rs) {  /* Coalesce matching registers right now. */
      ra_free(as, ir->r);
    } else if (ra_hasspill(regsp_spill(rs))) {
      if (ra_hasreg(ir->r))
        pass3 = 1;
    } else if (ra_used(ir)) {
      sloadins[rs] = (IRRef1)i;
      rset_set(live, rs);  /* Block live parent register. */
    }
    if (!ra_hasspill(regsp_spill(rs))) rset_clear(pallow, regsp_reg(rs));
  }

  /* Calculate stack frame adjustment. */
  spadj = asm_stack_adjust(as);
  spdelta = spadj - (int32_t)as->parent->spadjust;
  if (spdelta < 0) {  /* Don't shrink the stack frame. */
    spadj = (int32_t)as->parent->spadjust;
    spdelta = 0;
  }
  as->T->spadjust = (uint16_t)spadj;

  /* Reload spilled target registers. */
  if (pass2) {
    for (i = as->stopins; i > REF_BASE; i--) {
      IRIns *ir = IR(i);
      if (irt_ismarked(ir->t)) {
        RegSet mask;
        Reg r;
        RegSP rs;
        irt_clearmark(ir->t);
        rs = as->parentmap[i - REF_FIRST];
        if (!ra_hasspill(regsp_spill(rs)))
          ra_sethint(ir->r, rs);  /* Hint may be gone, set it again. */
        else if (sps_scale(regsp_spill(rs))+spdelta == sps_scale(ir->s))
          continue;  /* Same spill slot, do nothing. */
        mask = ((!LJ_SOFTFP && irt_isfp(ir->t)) ? RSET_FPR : RSET_GPR) & allow;
        if (mask == RSET_EMPTY)
          lj_trace_err(as->J, LJ_TRERR_NYICOAL);
        r = ra_allocref(as, i, mask);
        ra_save(as, ir, r);
        rset_clear(allow, r);
        if (r == rs) {  /* Coalesce matching registers right now. */
          ra_free(as, r);
          rset_clear(live, r);
        } else if (ra_hasspill(regsp_spill(rs))) {
          pass3 = 1;
        }
        checkmclim(as);
      }
    }
  }

  /* Store trace number and adjust stack frame relative to the parent. */
  emit_setvmstate(as, (int32_t)as->T->traceno);
  emit_spsub(as, spdelta);

#if !LJ_TARGET_X86ORX64
  /* Restore BASE register from parent spill slot. */
  if (ra_hasspill(irp->s))
    emit_spload(as, IR(REF_BASE), IR(REF_BASE)->r, sps_scale(irp->s));
#endif

  /* Restore target registers from parent spill slots. */
  if (pass3) {
    RegSet work = ~as->freeset & RSET_ALL;
    while (work) {
      Reg r = rset_pickbot(work);
      IRRef ref = regcost_ref(as->cost[r]);
      RegSP rs = as->parentmap[ref - REF_FIRST];
      rset_clear(work, r);
      if (ra_hasspill(regsp_spill(rs))) {
        int32_t ofs = sps_scale(regsp_spill(rs));
        ra_free(as, r);
        emit_spload(as, IR(ref), r, ofs);
        checkmclim(as);
      }
    }
  }

  /* Shuffle registers to match up target regs with parent regs. */
  for (;;) {
    RegSet work;

    /* Repeatedly coalesce free live registers by moving to their target. */
    while ((work = as->freeset & live) != RSET_EMPTY) {
      Reg rp = rset_pickbot(work);
      IRIns *ir = IR(sloadins[rp]);
      rset_clear(live, rp);
      rset_clear(allow, rp);
      ra_free(as, ir->r);
      emit_movrr(as, ir, ir->r, rp);
      checkmclim(as);
    }

    /* We're done if no live registers remain. */
    if (live == RSET_EMPTY)
      break;

    /* Break cycles by renaming one target to a temp. register. */
    if (live & RSET_GPR) {
      RegSet tmpset = as->freeset & ~live & allow & RSET_GPR;
      if (tmpset == RSET_EMPTY)
        lj_trace_err(as->J, LJ_TRERR_NYICOAL);
      ra_rename(as, rset_pickbot(live & RSET_GPR), rset_pickbot(tmpset));
    }
    if (!LJ_SOFTFP && (live & RSET_FPR)) {
      RegSet tmpset = as->freeset & ~live & allow & RSET_FPR;
      if (tmpset == RSET_EMPTY)
        lj_trace_err(as->J, LJ_TRERR_NYICOAL);
      ra_rename(as, rset_pickbot(live & RSET_FPR), rset_pickbot(tmpset));
    }
    checkmclim(as);
    /* Continue with coalescing to fix up the broken cycle(s). */
  }

  /* Inherit top stack slot already checked by parent trace. */
  as->T->topslot = as->parent->topslot;
  if (as->topslot > as->T->topslot) {  /* Need to check for higher slot? */
#ifdef EXITSTATE_CHECKEXIT
    /* Highest exit + 1 indicates stack check. */
    ExitNo exitno = as->T->nsnap;
#else
    /* Reuse the parent exit in the context of the parent trace. */
    ExitNo exitno = as->J->exitno;
#endif
    as->T->topslot = (uint8_t)as->topslot;  /* Remember for child traces. */
    asm_stack_check(as, as->topslot, irp, pallow, exitno);
  }
}

/* -- Tail of trace ------------------------------------------------------- */

/* Get base slot for a snapshot. */
static BCReg asm_baseslot(ASMState *as, SnapShot *snap, int *gotframe)
{
  SnapEntry *map = &as->T->snapmap[snap->mapofs];
  MSize n;
  for (n = snap->nent; n > 0; n--) {
    SnapEntry sn = map[n-1];
    if ((sn & SNAP_FRAME)) {
      *gotframe = 1;
      return snap_slot(sn) - LJ_FR2;
    }
  }
  return 0;
}

/* Link to another trace. */
static void asm_tail_link(ASMState *as)
{
  SnapNo snapno = as->T->nsnap-1;  /* Last snapshot. */
  SnapShot *snap = &as->T->snap[snapno];
  int gotframe = 0;
  BCReg baseslot = asm_baseslot(as, snap, &gotframe);

  as->topslot = snap->topslot;
  checkmclim(as);
  ra_allocref(as, REF_BASE, RID2RSET(RID_BASE));

  if (as->T->link == 0) {
    /* Setup fixed registers for exit to interpreter. */
    const BCIns *pc = snap_pc(&as->T->snapmap[snap->mapofs + snap->nent]);
    int32_t mres;
    if (bc_op(*pc) == BC_JLOOP) {  /* NYI: find a better way to do this. */
      BCIns *retpc = &traceref(as->J, bc_d(*pc))->startins;
      if (bc_isret(bc_op(*retpc)))
        pc = retpc;
    }
#if LJ_GC64
    emit_loadu64(as, RID_LPC, u64ptr(pc));
#else
    ra_allockreg(as, i32ptr(J2GG(as->J)->dispatch), RID_DISPATCH);
    ra_allockreg(as, i32ptr(pc), RID_LPC);
#endif
    mres = (int32_t)(snap->nslots - baseslot - LJ_FR2);
    switch (bc_op(*pc)) {
    case BC_CALLM: case BC_CALLMT:
      mres -= (int32_t)(1 + LJ_FR2 + bc_a(*pc) + bc_c(*pc)); break;
    case BC_RETM: mres -= (int32_t)(bc_a(*pc) + bc_d(*pc)); break;
    case BC_TSETM: mres -= (int32_t)bc_a(*pc); break;
    default: if (bc_op(*pc) < BC_FUNCF) mres = 0; break;
    }
    ra_allockreg(as, mres, RID_RET);  /* Return MULTRES or 0. */
  } else if (baseslot) {
    /* Save modified BASE for linking to trace with higher start frame. */
    emit_setgl(as, RID_BASE, jit_base);
  }
  emit_addptr(as, RID_BASE, 8*(int32_t)baseslot);

  if (as->J->ktrace) {  /* Patch ktrace slot with the final GCtrace pointer. */
    setgcref(IR(as->J->ktrace)[LJ_GC64].gcr, obj2gco(as->J->curfinal));
    IR(as->J->ktrace)->o = IR_KGC;
  }

  /* Sync the interpreter state with the on-trace state. */
  asm_stack_restore(as, snap);

  /* Root traces that add frames need to check the stack at the end. */
  if (!as->parent && gotframe)
    asm_stack_check(as, as->topslot, NULL, as->freeset & RSET_GPR, snapno);
}

/* -- Trace setup --------------------------------------------------------- */

/* Clear reg/sp for all instructions and add register hints. */
static void asm_setup_regsp(ASMState *as)
{
  GCtrace *T = as->T;
  int sink = T->sinktags;
  IRRef nins = T->nins;
  IRIns *ir, *lastir;
  int inloop;
#if LJ_TARGET_ARM
  uint32_t rload = 0xa6402a64;
#endif

  ra_setup(as);

  /* Clear reg/sp for constants. */
  for (ir = IR(T->nk), lastir = IR(REF_BASE); ir < lastir; ir++) {
    ir->prev = REGSP_INIT;
    if (irt_is64(ir->t) && ir->o != IR_KNULL) {
#if LJ_GC64
      /* The false-positive of irt_is64() for ASMREF_L (REF_NIL) is OK here. */
      ir->i = 0;  /* Will become non-zero only for RIP-relative addresses. */
#else
      /* Make life easier for backends by putting address of constant in i. */
      ir->i = (int32_t)(intptr_t)(ir+1);
#endif
      ir++;
    }
  }

  /* REF_BASE is used for implicit references to the BASE register. */
  lastir->prev = REGSP_HINT(RID_BASE);

  as->snaprename = nins;
  as->snapref = nins;
  as->snapno = T->nsnap;
  as->snapalloc = 0;

  as->stopins = REF_BASE;
  as->orignins = nins;
  as->curins = nins;

  /* Setup register hints for parent link instructions. */
  ir = IR(REF_FIRST);
  if (as->parent) {
    uint16_t *p;
    lastir = lj_snap_regspmap(as->J, as->parent, as->J->exitno, ir);
    if (lastir - ir > LJ_MAX_JSLOTS)
      lj_trace_err(as->J, LJ_TRERR_NYICOAL);
    as->stopins = (IRRef)((lastir-1) - as->ir);
    for (p = as->parentmap; ir < lastir; ir++) {
      RegSP rs = ir->prev;
      *p++ = (uint16_t)rs;  /* Copy original parent RegSP to parentmap. */
      if (!ra_hasspill(regsp_spill(rs)))
        ir->prev = (uint16_t)REGSP_HINT(regsp_reg(rs));
      else
        ir->prev = REGSP_INIT;
    }
  }

  inloop = 0;
  as->evenspill = SPS_FIRST;
  for (lastir = IR(nins); ir < lastir; ir++) {
    if (sink) {
      if (ir->r == RID_SINK)
        continue;
      if (ir->r == RID_SUNK) {  /* Revert after ASM restart. */
        ir->r = RID_SINK;
        continue;
      }
    }
    switch (ir->o) {
    case IR_LOOP:
      inloop = 1;
      break;
#if LJ_TARGET_ARM
    case IR_SLOAD:
      if (!((ir->op2 & IRSLOAD_TYPECHECK) || (ir+1)->o == IR_HIOP))
        break;
      /* fallthrough */
    case IR_ALOAD: case IR_HLOAD: case IR_ULOAD: case IR_VLOAD:
      if (!LJ_SOFTFP && irt_isnum(ir->t)) break;
      ir->prev = (uint16_t)REGSP_HINT((rload & 15));
      rload = lj_ror(rload, 4);
      continue;
#endif
    case IR_CALLXS: {
      CCallInfo ci;
      ci.flags = asm_callx_flags(as, ir);
      ir->prev = asm_setup_call_slots(as, ir, &ci);
      if (inloop)
        as->modset |= RSET_SCRATCH;
      continue;
      }
    case IR_CALLN: case IR_CALLA: case IR_CALLL: case IR_CALLS: {
      const CCallInfo *ci = &lj_ir_callinfo[ir->op2];
      ir->prev = asm_setup_call_slots(as, ir, ci);
      if (inloop)
        as->modset |= (ci->flags & CCI_NOFPRCLOBBER) ?
                      (RSET_SCRATCH & ~RSET_FPR) : RSET_SCRATCH;
      continue;
      }
#if LJ_SOFTFP || (LJ_32 && LJ_HASFFI)
    case IR_HIOP:
      switch ((ir-1)->o) {
#if LJ_SOFTFP && LJ_TARGET_ARM
      case IR_SLOAD: case IR_ALOAD: case IR_HLOAD: case IR_ULOAD: case IR_VLOAD:
        if (ra_hashint((ir-1)->r)) {
          ir->prev = (ir-1)->prev + 1;
          continue;
        }
        break;
#endif
#if !LJ_SOFTFP && LJ_NEED_FP64
      case IR_CONV:
        if (irt_isfp((ir-1)->t)) {
          ir->prev = REGSP_HINT(RID_FPRET);
          continue;
        }
#endif
      /* fallthrough */
      case IR_CALLN: case IR_CALLXS:
#if LJ_SOFTFP
      case IR_MIN: case IR_MAX:
#endif
        (ir-1)->prev = REGSP_HINT(RID_RETLO);
        ir->prev = REGSP_HINT(RID_RETHI);
        continue;
      default:
        break;
      }
      break;
#endif
#if LJ_SOFTFP
    case IR_MIN: case IR_MAX:
      if ((ir+1)->o != IR_HIOP) break;
#endif
    /* fallthrough */
    /* C calls evict all scratch regs and return results in RID_RET. */
    case IR_SNEW: case IR_XSNEW: case IR_NEWREF: case IR_BUFPUT:
      if (REGARG_NUMGPR < 3 && as->evenspill < 3)
        as->evenspill = 3;  /* lj_str_new and lj_tab_newkey need 3 args. */
#if LJ_TARGET_X86 && LJ_HASFFI
      if (0) {
    case IR_CNEW:
        if (ir->op2 != REF_NIL && as->evenspill < 4)
          as->evenspill = 4;  /* lj_cdata_newv needs 4 args. */
      }
      /* fallthrough */
#else
      /* fallthrough */
    case IR_CNEW:
#endif
      /* fallthrough */
    case IR_TNEW: case IR_TDUP: case IR_CNEWI: case IR_TOSTR:
    case IR_BUFSTR:
      ir->prev = REGSP_HINT(RID_RET);
      if (inloop)
        as->modset = RSET_SCRATCH;
      continue;
    case IR_STRTO: case IR_OBAR:
      if (inloop)
        as->modset = RSET_SCRATCH;
      break;
#if !LJ_SOFTFP
#if !LJ_TARGET_X86ORX64
    case IR_LDEXP:
#endif
#endif
      /* fallthrough */
    case IR_POW:
      if (!LJ_SOFTFP && irt_isnum(ir->t)) {
        if (inloop)
          as->modset |= RSET_SCRATCH;
#if LJ_TARGET_X86
        if (irt_isnum(IR(ir->op2)->t)) {
          if (as->evenspill < 4)  /* Leave room to call pow(). */
            as->evenspill = 4;
        }
        break;
#else
        ir->prev = REGSP_HINT(RID_FPRET);
        continue;
#endif
      }
      /* fallthrough */ /* for integer POW */
    case IR_DIV: case IR_MOD:
      if (!irt_isnum(ir->t)) {
        ir->prev = REGSP_HINT(RID_RET);
        if (inloop)
          as->modset |= (RSET_SCRATCH & RSET_GPR);
        continue;
      }
      break;
    case IR_FPMATH:
#if LJ_TARGET_X86ORX64
      if (ir->op2 <= IRFPM_TRUNC) {
        if (!(as->flags & JIT_F_SSE4_1)) {
          ir->prev = REGSP_HINT(RID_XMM0);
          if (inloop)
            as->modset |= RSET_RANGE(RID_XMM0, RID_XMM3+1)|RID2RSET(RID_EAX);
          continue;
        }
        break;
      }
#endif
      if (inloop)
        as->modset |= RSET_SCRATCH;
#if LJ_TARGET_X86
      break;
#else
      ir->prev = REGSP_HINT(RID_FPRET);
      continue;
#endif
#if LJ_TARGET_X86ORX64
    /* Non-constant shift counts need to be in RID_ECX on x86/x64. */
    case IR_BSHL: case IR_BSHR: case IR_BSAR:
      if ((as->flags & JIT_F_BMI2))  /* Except if BMI2 is available. */
        break;
      /* fallthrough */
    case IR_BROL: case IR_BROR:
      if (!irref_isk(ir->op2) && !ra_hashint(IR(ir->op2)->r)) {
        IR(ir->op2)->r = REGSP_HINT(RID_ECX);
        if (inloop)
          rset_set(as->modset, RID_ECX);
      }
      break;
#endif
    /* Do not propagate hints across type conversions or loads. */
    case IR_TOBIT:
    case IR_XLOAD:
#if !LJ_TARGET_ARM
    case IR_ALOAD: case IR_HLOAD: case IR_ULOAD: case IR_VLOAD:
#endif
      break;
    case IR_CONV:
      if (irt_isfp(ir->t) || (ir->op2 & IRCONV_SRCMASK) == IRT_NUM ||
          (ir->op2 & IRCONV_SRCMASK) == IRT_FLOAT)
        break;
      /* fallthrough */
    default:
      /* Propagate hints across likely 'op reg, imm' or 'op reg'. */
      if (irref_isk(ir->op2) && !irref_isk(ir->op1) &&
          ra_hashint(regsp_reg(IR(ir->op1)->prev))) {
        ir->prev = IR(ir->op1)->prev;
        continue;
      }
      break;
    }
    ir->prev = REGSP_INIT;
  }
  if ((as->evenspill & 1))
    as->oddspill = as->evenspill++;
  else
    as->oddspill = 0;
}

/* -- Assembler core ------------------------------------------------------ */

/* Assemble a trace. */
void lj_asm_trace(jit_State *J, GCtrace *T)
{
  ASMState as_;
  ASMState *as = &as_;

  /* Remove nops/renames left over from ASM restart due to LJ_TRERR_MCODELM. */
  {
    IRRef nins = T->nins;
    IRIns *ir = &T->ir[nins-1];
    if (ir->o == IR_NOP || ir->o == IR_RENAME) {
      do { ir--; nins--; } while (ir->o == IR_NOP || ir->o == IR_RENAME);
      T->nins = nins;
    }
  }

  /* Ensure an initialized instruction beyond the last one for HIOP checks. */
  /* This also allows one RENAME to be added without reallocating curfinal. */
  as->orignins = lj_ir_nextins(J);
  J->cur.ir[as->orignins].o = IR_NOP;

  /* Setup initial state. Copy some fields to reduce indirections. */
  as->J = J;
  as->T = T;
  J->curfinal = lj_trace_alloc(J->L, T);  /* This copies the IR, too. */
  as->flags = J->flags;
  as->loopref = J->loopref;
  as->realign = NULL;
  as->loopinv = 0;
  as->parent = J->parent ? traceref(J, J->parent) : NULL;

  /* Reserve MCode memory. */
  as->mctop = as->mctoporig = lj_mcode_reserve(J, &as->mcbot);
  as->mcp = as->mctop;
  as->mclim = as->mcbot + MCLIM_REDZONE;
  asm_setup_target(as);

  /*
  ** This is a loop, because the MCode may have to be (re-)assembled
  ** multiple times:
  **
  ** 1. as->realign is set (and the assembly aborted), if the arch-specific
  **    backend wants the MCode to be aligned differently.
  **
  **    This is currently only the case on x86/x64, where small loops get
  **    an aligned loop body plus a short branch. Not much effort is wasted,
  **    because the abort happens very quickly and only once.
  **
  ** 2. The IR is immovable, since the MCode embeds pointers to various
  **    constants inside the IR. But RENAMEs may need to be added to the IR
  **    during assembly, which might grow and reallocate the IR. We check
  **    at the end if the IR (in J->cur.ir) has actually grown, resize the
  **    copy (in J->curfinal.ir) and try again.
  **
  **    95% of all traces have zero RENAMEs, 3% have one RENAME, 1.5% have
  **    2 RENAMEs and only 0.5% have more than that. That's why we opt to
  **    always have one spare slot in the IR (see above), which means we
  **    have to redo the assembly for only ~2% of all traces.
  **
  **    Very, very rarely, this needs to be done repeatedly, since the
  **    location of constants inside the IR (actually, reachability from
  **    a global pointer) may affect register allocation and thus the
  **    number of RENAMEs.
  */
  for (;;) {
    as->mcp = as->mctop;
#ifdef LUA_USE_ASSERT
    as->mcp_prev = as->mcp;
#endif
    as->ir = J->curfinal->ir;  /* Use the copied IR. */
    as->curins = J->cur.nins = as->orignins;

    RA_DBG_START();
    RA_DBGX((as, "===== STOP ====="));

    /* General trace setup. Emit tail of trace. */
    asm_tail_prep(as);
    as->mcloop = NULL;
    as->flagmcp = NULL;
    as->topslot = 0;
    as->gcsteps = 0;
    as->sectref = as->loopref;
    as->fuseref = (as->flags & JIT_F_OPT_FUSE) ? as->loopref : FUSE_DISABLED;
    asm_setup_regsp(as);
    if (!as->loopref)
      asm_tail_link(as);

    /* Assemble a trace in linear backwards order. */
    for (as->curins--; as->curins > as->stopins; as->curins--) {
      IRIns *ir = IR(as->curins);
      /* 64 bit types handled by SPLIT for 32 bit archs. */
      lj_assertA(!(LJ_32 && irt_isint64(ir->t)),
                 "IR %04d has unsplit 64 bit type",
                 (int)(ir - as->ir) - REF_BIAS);
      asm_snap_prev(as);
      if (!ra_used(ir) && !ir_sideeff(ir) && (as->flags & JIT_F_OPT_DCE))
        continue;  /* Dead-code elimination can be soooo easy. */
      if (irt_isguard(ir->t))
        asm_snap_prep(as);
      RA_DBG_REF();
      checkmclim(as);
      asm_ir(as, ir);
    }

    if (as->realign && J->curfinal->nins >= T->nins)
      continue;  /* Retry in case only the MCode needs to be realigned. */

    /* Emit head of trace. */
    RA_DBG_REF();
    checkmclim(as);
    if (as->gcsteps > 0) {
      as->curins = as->T->snap[0].ref;
      asm_snap_prep(as);  /* The GC check is a guard. */
      asm_gc_check(as);
      as->curins = as->stopins;
    }
    ra_evictk(as);
    if (as->parent)
      asm_head_side(as);
    else
      asm_head_root(as);
    asm_phi_fixup(as);

    if (J->curfinal->nins >= T->nins) {  /* IR didn't grow? */
      lj_assertA(J->curfinal->nk == T->nk, "unexpected IR constant growth");
      memcpy(J->curfinal->ir + as->orignins, T->ir + as->orignins,
             (T->nins - as->orignins) * sizeof(IRIns));  /* Copy RENAMEs. */
      T->nins = J->curfinal->nins;
      /* Fill mcofs of any unprocessed snapshots. */
      as->curins = REF_FIRST;
      asm_snap_prev(as);
      break;  /* Done. */
    }

    /* Otherwise try again with a bigger IR. */
    lj_trace_free(J2G(J), J->curfinal);
    J->curfinal = NULL;  /* In case lj_trace_alloc() OOMs. */
    J->curfinal = lj_trace_alloc(J->L, T);
    as->realign = NULL;
  }

  RA_DBGX((as, "===== START ===="));
  RA_DBG_FLUSH();
  if (as->freeset != RSET_ALL)
    lj_trace_err(as->J, LJ_TRERR_BADRA);  /* Ouch! Should never happen. */

  /* Set trace entry point before fixing up tail to allow link to self. */
  T->mcode = as->mcp;
  T->mcloop = as->mcloop ? (MSize)((char *)as->mcloop - (char *)as->mcp) : 0;
  if (!as->loopref)
    asm_tail_fixup(as, T->link);  /* Note: this may change as->mctop! */
  T->szmcode = (MSize)((char *)as->mctop - (char *)as->mcp);
  asm_snap_fixup_mcofs(as);
#if LJ_TARGET_MCODE_FIXUP
  asm_mcode_fixup(T->mcode, T->szmcode);
#endif
  lj_mcode_sync(T->mcode, as->mctoporig);
}

#undef IR

#endif

tarantool / luajit / 8534112221

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