6482677868

Committed 11 Oct 2023 12:31PM UTC coverage: 88.235% (-0.06%) from 88.296%

Build # 6482677868

Build Type

push

github

Committed by

Buristan

Commit Message

Fix base register coalescing in side trace.

Thanks to Sergey Kaplun, NiLuJe and Peter Cawley.

(cherry-picked from commit aa2db7ebd)

The previous patch fixed just part of the problem with the register
coalesing. For example, the parent base register may be used inside the
parent or child register sets when it shouldn't. This leads to incorrect
register allocations, which may lead to crashes or undefined behaviour.
This patch fixes it by excluding the parent base register from both
register sets.

The test case for this patch doesn't fail before the commit since it
requires specific register allocation, which is hard to construct and
very fragile. Due to the lack of ideal sync with the upstream
repository, the test is passed before the patch.
It should become correct in future patches.

Resolves tarantool/tarantool#8767
Part of tarantool/tarantool#9145

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

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Source File
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95.91

/src/lj_opt_mem.c

/*
** Memory access optimizations.
** AA: Alias Analysis using high-level semantic disambiguation.
** FWD: Load Forwarding (L2L) + Store Forwarding (S2L).
** DSE: Dead-Store Elimination.
** Copyright (C) 2005-2017 Mike Pall. See Copyright Notice in luajit.h
*/

#define lj_opt_mem_c
#define LUA_CORE

#include "lj_obj.h"

#if LJ_HASJIT

#include "lj_tab.h"
#include "lj_ir.h"
#include "lj_jit.h"
#include "lj_iropt.h"
#include "lj_ircall.h"
#include "lj_dispatch.h"

/* Some local macros to save typing. Undef'd at the end. */
#define IR(ref)                (&J->cur.ir[(ref)])
#define fins                (&J->fold.ins)
#define fleft                (J->fold.left)
#define fright                (J->fold.right)

/*
** Caveat #1: return value is not always a TRef -- only use with tref_ref().
** Caveat #2: FWD relies on active CSE for xREF operands -- see lj_opt_fold().
*/

/* Return values from alias analysis. */
typedef enum {
  ALIAS_NO,        /* The two refs CANNOT alias (exact). */
  ALIAS_MAY,        /* The two refs MAY alias (inexact). */
  ALIAS_MUST        /* The two refs MUST alias (exact). */
} AliasRet;

/* -- ALOAD/HLOAD forwarding and ASTORE/HSTORE elimination ---------------- */

/* Simplified escape analysis: check for intervening stores. */
static AliasRet aa_escape(jit_State *J, IRIns *ir, IRIns *stop)
{
  IRRef ref = (IRRef)(ir - J->cur.ir);  /* The ref that might be stored. */
  for (ir++; ir < stop; ir++)
    if (ir->op2 == ref &&
        (ir->o == IR_ASTORE || ir->o == IR_HSTORE ||
         ir->o == IR_USTORE || ir->o == IR_FSTORE))
      return ALIAS_MAY;  /* Reference was stored and might alias. */
  return ALIAS_NO;  /* Reference was not stored. */
}

/* Alias analysis for two different table references. */
static AliasRet aa_table(jit_State *J, IRRef ta, IRRef tb)
{
  IRIns *taba = IR(ta), *tabb = IR(tb);
  int newa, newb;
  lj_assertJ(ta != tb, "bad usage");
  lj_assertJ(irt_istab(taba->t) && irt_istab(tabb->t), "bad usage");
  /* Disambiguate new allocations. */
  newa = (taba->o == IR_TNEW || taba->o == IR_TDUP);
  newb = (tabb->o == IR_TNEW || tabb->o == IR_TDUP);
  if (newa && newb)
    return ALIAS_NO;  /* Two different allocations never alias. */
  if (newb) {  /* At least one allocation? */
    IRIns *tmp = taba; taba = tabb; tabb = tmp;
  } else if (!newa) {
    return ALIAS_MAY;  /* Anything else: we just don't know. */
  }
  return aa_escape(J, taba, tabb);
}

/* Alias analysis for array and hash access using key-based disambiguation. */
static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
{
  IRRef ka = refa->op2;
  IRRef kb = refb->op2;
  IRIns *keya, *keyb;
  IRRef ta, tb;
  if (refa == refb)
    return ALIAS_MUST;  /* Shortcut for same refs. */
  keya = IR(ka);
  if (keya->o == IR_KSLOT) { ka = keya->op1; keya = IR(ka); }
  keyb = IR(kb);
  if (keyb->o == IR_KSLOT) { kb = keyb->op1; keyb = IR(kb); }
  ta = (refa->o==IR_HREFK || refa->o==IR_AREF) ? IR(refa->op1)->op1 : refa->op1;
  tb = (refb->o==IR_HREFK || refb->o==IR_AREF) ? IR(refb->op1)->op1 : refb->op1;
  if (ka == kb) {
    /* Same key. Check for same table with different ref (NEWREF vs. HREF). */
    if (ta == tb)
      return ALIAS_MUST;  /* Same key, same table. */
    else
      return aa_table(J, ta, tb);  /* Same key, possibly different table. */
  }
  if (irref_isk(ka) && irref_isk(kb))
    return ALIAS_NO;  /* Different constant keys. */
  if (refa->o == IR_AREF) {
    /* Disambiguate array references based on index arithmetic. */
    int32_t ofsa = 0, ofsb = 0;
    IRRef basea = ka, baseb = kb;
    lj_assertJ(refb->o == IR_AREF, "expected AREF");
    /* Gather base and offset from t[base] or t[base+-ofs]. */
    if (keya->o == IR_ADD && irref_isk(keya->op2)) {
      basea = keya->op1;
      ofsa = IR(keya->op2)->i;
      if (basea == kb && ofsa != 0)
        return ALIAS_NO;  /* t[base+-ofs] vs. t[base]. */
    }
    if (keyb->o == IR_ADD && irref_isk(keyb->op2)) {
      baseb = keyb->op1;
      ofsb = IR(keyb->op2)->i;
      if (ka == baseb && ofsb != 0)
        return ALIAS_NO;  /* t[base] vs. t[base+-ofs]. */
    }
    if (basea == baseb && ofsa != ofsb)
      return ALIAS_NO;  /* t[base+-o1] vs. t[base+-o2] and o1 != o2. */
  } else {
    /* Disambiguate hash references based on the type of their keys. */
    lj_assertJ((refa->o==IR_HREF || refa->o==IR_HREFK || refa->o==IR_NEWREF) &&
               (refb->o==IR_HREF || refb->o==IR_HREFK || refb->o==IR_NEWREF),
               "bad xREF IR op %d or %d", refa->o, refb->o);
    if (!irt_sametype(keya->t, keyb->t))
      return ALIAS_NO;  /* Different key types. */
  }
  if (ta == tb)
    return ALIAS_MAY;  /* Same table, cannot disambiguate keys. */
  else
    return aa_table(J, ta, tb);  /* Try to disambiguate tables. */
}

/* Array and hash load forwarding. */
static TRef fwd_ahload(jit_State *J, IRRef xref)
{
  IRIns *xr = IR(xref);
  IRRef lim = xref;  /* Search limit. */
  IRRef ref;

  /* Search for conflicting stores. */
  ref = J->chain[fins->o+IRDELTA_L2S];
  while (ref > xref) {
    IRIns *store = IR(ref);
    switch (aa_ahref(J, xr, IR(store->op1))) {
    case ALIAS_NO:   break;  /* Continue searching. */
    case ALIAS_MAY:  lim = ref; goto cselim;  /* Limit search for load. */
    case ALIAS_MUST: return store->op2;  /* Store forwarding. */
    }
    ref = store->prev;
  }

  /* No conflicting store (yet): const-fold loads from allocations. */
  {
    IRIns *ir = (xr->o == IR_HREFK || xr->o == IR_AREF) ? IR(xr->op1) : xr;
    IRRef tab = ir->op1;
    ir = IR(tab);
    if (ir->o == IR_TNEW || (ir->o == IR_TDUP && irref_isk(xr->op2))) {
      /* A NEWREF with a number key may end up pointing to the array part.
      ** But it's referenced from HSTORE and not found in the ASTORE chain.
      ** Or a NEWREF may rehash the table and move unrelated number keys.
      ** For now simply consider this a conflict without forwarding anything.
      */
      if (xr->o == IR_AREF) {
        IRRef ref2 = J->chain[IR_NEWREF];
        while (ref2 > tab) {
          IRIns *newref = IR(ref2);
          if (irt_isnum(IR(newref->op2)->t))
            goto cselim;
          ref2 = newref->prev;
        }
      } else {
        IRIns *key = IR(xr->op2);
        if (key->o == IR_KSLOT) key = IR(key->op1);
        if (irt_isnum(key->t) && J->chain[IR_NEWREF] > tab)
          goto cselim;
      }
      /* NEWREF inhibits CSE for HREF, and dependent FLOADs from HREFK/AREF.
      ** But the above search for conflicting stores was limited by xref.
      ** So continue searching, limited by the TNEW/TDUP. Store forwarding
      ** is ok, too. A conflict does NOT limit the search for a matching load.
      */
      while (ref > tab) {
        IRIns *store = IR(ref);
        switch (aa_ahref(J, xr, IR(store->op1))) {
        case ALIAS_NO:   break;  /* Continue searching. */
        case ALIAS_MAY:  goto cselim;  /* Conflicting store. */
        case ALIAS_MUST: return store->op2;  /* Store forwarding. */
        }
        ref = store->prev;
      }
      if (ir->o == IR_TNEW && !irt_isnil(fins->t))
        return 0;  /* Type instability in loop-carried dependency. */
      if (irt_ispri(fins->t)) {
        return TREF_PRI(irt_type(fins->t));
      } else if (irt_isnum(fins->t) || (LJ_DUALNUM && irt_isint(fins->t)) ||
                 irt_isstr(fins->t)) {
        TValue keyv;
        cTValue *tv;
        IRIns *key = IR(xr->op2);
        if (key->o == IR_KSLOT) key = IR(key->op1);
        lj_ir_kvalue(J->L, &keyv, key);
        tv = lj_tab_get(J->L, ir_ktab(IR(ir->op1)), &keyv);
        if (itype2irt(tv) != irt_type(fins->t))
          return 0;  /* Type instability in loop-carried dependency. */
        if (irt_isnum(fins->t))
          return lj_ir_knum_u64(J, tv->u64);
        else if (LJ_DUALNUM && irt_isint(fins->t))
          return lj_ir_kint(J, intV(tv));
        else
          return lj_ir_kstr(J, strV(tv));
      }
      /* Othwerwise: don't intern as a constant. */
    }
  }

cselim:
  /* Try to find a matching load. Below the conflicting store, if any. */
  ref = J->chain[fins->o];
  while (ref > lim) {
    IRIns *load = IR(ref);
    if (load->op1 == xref)
      return ref;  /* Load forwarding. */
    ref = load->prev;
  }
  return 0;  /* Conflict or no match. */
}

/* Reassociate ALOAD across PHIs to handle t[i-1] forwarding case. */
static TRef fwd_aload_reassoc(jit_State *J)
{
  IRIns *irx = IR(fins->op1);
  IRIns *key = IR(irx->op2);
  if (key->o == IR_ADD && irref_isk(key->op2)) {
    IRIns *add2 = IR(key->op1);
    if (add2->o == IR_ADD && irref_isk(add2->op2) &&
        IR(key->op2)->i == -IR(add2->op2)->i) {
      IRRef ref = J->chain[IR_AREF];
      IRRef lim = add2->op1;
      if (irx->op1 > lim) lim = irx->op1;
      while (ref > lim) {
        IRIns *ir = IR(ref);
        if (ir->op1 == irx->op1 && ir->op2 == add2->op1)
          return fwd_ahload(J, ref);
        ref = ir->prev;
      }
    }
  }
  return 0;
}

/* ALOAD forwarding. */
TRef LJ_FASTCALL lj_opt_fwd_aload(jit_State *J)
{
  IRRef ref;
  if ((ref = fwd_ahload(J, fins->op1)) ||
      (ref = fwd_aload_reassoc(J)))
    return ref;
  return EMITFOLD;
}

/* HLOAD forwarding. */
TRef LJ_FASTCALL lj_opt_fwd_hload(jit_State *J)
{
  IRRef ref = fwd_ahload(J, fins->op1);
  if (ref)
    return ref;
  return EMITFOLD;
}

/* HREFK forwarding. */
TRef LJ_FASTCALL lj_opt_fwd_hrefk(jit_State *J)
{
  IRRef tab = fleft->op1;
  IRRef ref = J->chain[IR_NEWREF];
  while (ref > tab) {
    IRIns *newref = IR(ref);
    if (tab == newref->op1) {
      if (fright->op1 == newref->op2)
        return ref;  /* Forward from NEWREF. */
      else
        goto docse;
    } else if (aa_table(J, tab, newref->op1) != ALIAS_NO) {
      goto docse;
    }
    ref = newref->prev;
  }
  /* No conflicting NEWREF: key location unchanged for HREFK of TDUP. */
  if (IR(tab)->o == IR_TDUP)
    fins->t.irt &= ~IRT_GUARD;  /* Drop HREFK guard. */
docse:
  return CSEFOLD;
}

/* Check whether HREF of TNEW/TDUP can be folded to niltv. */
int LJ_FASTCALL lj_opt_fwd_href_nokey(jit_State *J)
{
  IRRef lim = fins->op1;  /* Search limit. */
  IRRef ref;

  /* The key for an ASTORE may end up in the hash part after a NEWREF. */
  if (irt_isnum(fright->t) && J->chain[IR_NEWREF] > lim) {
    ref = J->chain[IR_ASTORE];
    while (ref > lim) {
      if (ref < J->chain[IR_NEWREF])
        return 0;  /* Conflict. */
      ref = IR(ref)->prev;
    }
  }

  /* Search for conflicting stores. */
  ref = J->chain[IR_HSTORE];
  while (ref > lim) {
    IRIns *store = IR(ref);
    if (aa_ahref(J, fins, IR(store->op1)) != ALIAS_NO)
      return 0;  /* Conflict. */
    ref = store->prev;
  }

  return 1;  /* No conflict. Can fold to niltv. */
}

/* Check whether there's no aliasing table.clear. */
static int fwd_aa_tab_clear(jit_State *J, IRRef lim, IRRef ta)
{
  IRRef ref = J->chain[IR_CALLS];
  while (ref > lim) {
    IRIns *calls = IR(ref);
    if (calls->op2 == IRCALL_lj_tab_clear &&
        (ta == calls->op1 || aa_table(J, ta, calls->op1) != ALIAS_NO))
      return 0;  /* Conflict. */
    ref = calls->prev;
  }
  return 1;  /* No conflict. Can safely FOLD/CSE. */
}

/* Check whether there's no aliasing NEWREF/table.clear for the left operand. */
int LJ_FASTCALL lj_opt_fwd_tptr(jit_State *J, IRRef lim)
{
  IRRef ta = fins->op1;
  IRRef ref = J->chain[IR_NEWREF];
  while (ref > lim) {
    IRIns *newref = IR(ref);
    if (ta == newref->op1 || aa_table(J, ta, newref->op1) != ALIAS_NO)
      return 0;  /* Conflict. */
    ref = newref->prev;
  }
  return fwd_aa_tab_clear(J, lim, ta);
}

/* ASTORE/HSTORE elimination. */
TRef LJ_FASTCALL lj_opt_dse_ahstore(jit_State *J)
{
  IRRef xref = fins->op1;  /* xREF reference. */
  IRRef val = fins->op2;  /* Stored value reference. */
  IRIns *xr = IR(xref);
  IRRef1 *refp = &J->chain[fins->o];
  IRRef ref = *refp;
  while (ref > xref) {  /* Search for redundant or conflicting stores. */
    IRIns *store = IR(ref);
    switch (aa_ahref(J, xr, IR(store->op1))) {
    case ALIAS_NO:
      break;  /* Continue searching. */
    case ALIAS_MAY:        /* Store to MAYBE the same location. */
      if (store->op2 != val)  /* Conflict if the value is different. */
        goto doemit;
      break;  /* Otherwise continue searching. */
    case ALIAS_MUST:        /* Store to the same location. */
      if (store->op2 == val)  /* Same value: drop the new store. */
        return DROPFOLD;
      /* Different value: try to eliminate the redundant store. */
      if (ref > J->chain[IR_LOOP]) {  /* Quick check to avoid crossing LOOP. */
        IRIns *ir;
        /* Check for any intervening guards (includes conflicting loads). */
        for (ir = IR(J->cur.nins-1); ir > store; ir--)
          if (irt_isguard(ir->t) || ir->o == IR_CALLL)
            goto doemit;  /* No elimination possible. */
        /* Remove redundant store from chain and replace with NOP. */
        *refp = store->prev;
        store->o = IR_NOP;
        store->t.irt = IRT_NIL;
        store->op1 = store->op2 = 0;
        store->prev = 0;
        /* Now emit the new store instead. */
      }
      goto doemit;
    }
    ref = *(refp = &store->prev);
  }
doemit:
  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
}

/* -- ULOAD forwarding ---------------------------------------------------- */

/* The current alias analysis for upvalues is very simplistic. It only
** disambiguates between the unique upvalues of the same function.
** This is good enough for now, since most upvalues are read-only.
**
** A more precise analysis would be feasible with the help of the parser:
** generate a unique key for every upvalue, even across all prototypes.
** Lacking a realistic use-case, it's unclear whether this is beneficial.
*/
static AliasRet aa_uref(IRIns *refa, IRIns *refb)
{
  if (refa->o != refb->o)
    return ALIAS_NO;  /* Different UREFx type. */
  if (refa->op1 == refb->op1) {  /* Same function. */
    if (refa->op2 == refb->op2)
      return ALIAS_MUST;  /* Same function, same upvalue idx. */
    else
      return ALIAS_NO;  /* Same function, different upvalue idx. */
  } else {  /* Different functions, check disambiguation hash values. */
    if (((refa->op2 ^ refb->op2) & 0xff))
      return ALIAS_NO;  /* Upvalues with different hash values cannot alias. */
    else
      return ALIAS_MAY;  /* No conclusion can be drawn for same hash value. */
  }
}

/* ULOAD forwarding. */
TRef LJ_FASTCALL lj_opt_fwd_uload(jit_State *J)
{
  IRRef uref = fins->op1;
  IRRef lim = REF_BASE;  /* Search limit. */
  IRIns *xr = IR(uref);
  IRRef ref;

  /* Search for conflicting stores. */
  ref = J->chain[IR_USTORE];
  while (ref > lim) {
    IRIns *store = IR(ref);
    switch (aa_uref(xr, IR(store->op1))) {
    case ALIAS_NO:   break;  /* Continue searching. */
    case ALIAS_MAY:  lim = ref; goto cselim;  /* Limit search for load. */
    case ALIAS_MUST: return store->op2;  /* Store forwarding. */
    }
    ref = store->prev;
  }

cselim:
  /* Try to find a matching load. Below the conflicting store, if any. */

  ref = J->chain[IR_ULOAD];
  while (ref > lim) {
    IRIns *ir = IR(ref);
    if (ir->op1 == uref ||
        (IR(ir->op1)->op12 == IR(uref)->op12 && IR(ir->op1)->o == IR(uref)->o))
      return ref;  /* Match for identical or equal UREFx (non-CSEable UREFO). */
    ref = ir->prev;
  }
  return lj_ir_emit(J);
}

/* USTORE elimination. */
TRef LJ_FASTCALL lj_opt_dse_ustore(jit_State *J)
{
  IRRef xref = fins->op1;  /* xREF reference. */
  IRRef val = fins->op2;  /* Stored value reference. */
  IRIns *xr = IR(xref);
  IRRef1 *refp = &J->chain[IR_USTORE];
  IRRef ref = *refp;
  while (ref > xref) {  /* Search for redundant or conflicting stores. */
    IRIns *store = IR(ref);
    switch (aa_uref(xr, IR(store->op1))) {
    case ALIAS_NO:
      break;  /* Continue searching. */
    case ALIAS_MAY:        /* Store to MAYBE the same location. */
      if (store->op2 != val)  /* Conflict if the value is different. */
        goto doemit;
      break;  /* Otherwise continue searching. */
    case ALIAS_MUST:        /* Store to the same location. */
      if (store->op2 == val)  /* Same value: drop the new store. */
        return DROPFOLD;
      /* Different value: try to eliminate the redundant store. */
      if (ref > J->chain[IR_LOOP]) {  /* Quick check to avoid crossing LOOP. */
        IRIns *ir;
        /* Check for any intervening guards (includes conflicting loads). */
        for (ir = IR(J->cur.nins-1); ir > store; ir--)
          if (irt_isguard(ir->t))
            goto doemit;  /* No elimination possible. */
        /* Remove redundant store from chain and replace with NOP. */
        *refp = store->prev;
        store->o = IR_NOP;
        store->t.irt = IRT_NIL;
        store->op1 = store->op2 = 0;
        store->prev = 0;
        if (ref+1 < J->cur.nins &&
            store[1].o == IR_OBAR && store[1].op1 == xref) {
          IRRef1 *bp = &J->chain[IR_OBAR];
          IRIns *obar;
          for (obar = IR(*bp); *bp > ref+1; obar = IR(*bp))
            bp = &obar->prev;
          /* Remove OBAR, too. */
          *bp = obar->prev;
          obar->o = IR_NOP;
          obar->t.irt = IRT_NIL;
          obar->op1 = obar->op2 = 0;
          obar->prev = 0;
        }
        /* Now emit the new store instead. */
      }
      goto doemit;
    }
    ref = *(refp = &store->prev);
  }
doemit:
  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
}

/* -- FLOAD forwarding and FSTORE elimination ----------------------------- */

/* Alias analysis for field access.
** Field loads are cheap and field stores are rare.
** Simple disambiguation based on field types is good enough.
*/
static AliasRet aa_fref(jit_State *J, IRIns *refa, IRIns *refb)
{
  if (refa->op2 != refb->op2)
    return ALIAS_NO;  /* Different fields. */
  if (refa->op1 == refb->op1)
    return ALIAS_MUST;  /* Same field, same object. */
  else if (refa->op2 >= IRFL_TAB_META && refa->op2 <= IRFL_TAB_NOMM)
    return aa_table(J, refa->op1, refb->op1);  /* Disambiguate tables. */
  else
    return ALIAS_MAY;  /* Same field, possibly different object. */
}

/* Only the loads for mutable fields end up here (see FOLD). */
TRef LJ_FASTCALL lj_opt_fwd_fload(jit_State *J)
{
  IRRef oref = fins->op1;  /* Object reference. */
  IRRef fid = fins->op2;  /* Field ID. */
  IRRef lim = oref;  /* Search limit. */
  IRRef ref;

  /* Search for conflicting stores. */
  ref = J->chain[IR_FSTORE];
  while (ref > oref) {
    IRIns *store = IR(ref);
    switch (aa_fref(J, fins, IR(store->op1))) {
    case ALIAS_NO:   break;  /* Continue searching. */
    case ALIAS_MAY:  lim = ref; goto cselim;  /* Limit search for load. */
    case ALIAS_MUST: return store->op2;  /* Store forwarding. */
    }
    ref = store->prev;
  }

  /* No conflicting store: const-fold field loads from allocations. */
  if (fid == IRFL_TAB_META) {
    IRIns *ir = IR(oref);
    if (ir->o == IR_TNEW || ir->o == IR_TDUP)
      return lj_ir_knull(J, IRT_TAB);
  }

cselim:
  /* Try to find a matching load. Below the conflicting store, if any. */
  return lj_opt_cselim(J, lim);
}

/* FSTORE elimination. */
TRef LJ_FASTCALL lj_opt_dse_fstore(jit_State *J)
{
  IRRef fref = fins->op1;  /* FREF reference. */
  IRRef val = fins->op2;  /* Stored value reference. */
  IRIns *xr = IR(fref);
  IRRef1 *refp = &J->chain[IR_FSTORE];
  IRRef ref = *refp;
  while (ref > fref) {  /* Search for redundant or conflicting stores. */
    IRIns *store = IR(ref);
    switch (aa_fref(J, xr, IR(store->op1))) {
    case ALIAS_NO:
      break;  /* Continue searching. */
    case ALIAS_MAY:
      if (store->op2 != val)  /* Conflict if the value is different. */
        goto doemit;
      break;  /* Otherwise continue searching. */
    case ALIAS_MUST:
      if (store->op2 == val)  /* Same value: drop the new store. */
        return DROPFOLD;
      /* Different value: try to eliminate the redundant store. */
      if (ref > J->chain[IR_LOOP]) {  /* Quick check to avoid crossing LOOP. */
        IRIns *ir;
        /* Check for any intervening guards or conflicting loads. */
        for (ir = IR(J->cur.nins-1); ir > store; ir--)
          if (irt_isguard(ir->t) || (ir->o == IR_FLOAD && ir->op2 == xr->op2))
            goto doemit;  /* No elimination possible. */
        /* Remove redundant store from chain and replace with NOP. */
        *refp = store->prev;
        store->o = IR_NOP;
        store->t.irt = IRT_NIL;
        store->op1 = store->op2 = 0;
        store->prev = 0;
        /* Now emit the new store instead. */
      }
      goto doemit;
    }
    ref = *(refp = &store->prev);
  }
doemit:
  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
}

/* -- XLOAD forwarding and XSTORE elimination ----------------------------- */

/* Find cdata allocation for a reference (if any). */
static IRIns *aa_findcnew(jit_State *J, IRIns *ir)
{
  while (ir->o == IR_ADD) {
    if (!irref_isk(ir->op1)) {
      IRIns *ir1 = aa_findcnew(J, IR(ir->op1));  /* Left-recursion. */
      if (ir1) return ir1;
    }
    if (irref_isk(ir->op2)) return NULL;
    ir = IR(ir->op2);  /* Flatten right-recursion. */
  }
  return ir->o == IR_CNEW ? ir : NULL;
}

/* Alias analysis for two cdata allocations. */
static AliasRet aa_cnew(jit_State *J, IRIns *refa, IRIns *refb)
{
  IRIns *cnewa = aa_findcnew(J, refa);
  IRIns *cnewb = aa_findcnew(J, refb);
  if (cnewa == cnewb)
    return ALIAS_MAY;  /* Same allocation or neither is an allocation. */
  if (cnewa && cnewb)
    return ALIAS_NO;  /* Two different allocations never alias. */
  if (cnewb) { cnewa = cnewb; refb = refa; }
  return aa_escape(J, cnewa, refb);
}

/* Alias analysis for XLOAD/XSTORE. */
static AliasRet aa_xref(jit_State *J, IRIns *refa, IRIns *xa, IRIns *xb)
{
  ptrdiff_t ofsa = 0, ofsb = 0;
  IRIns *refb = IR(xb->op1);
  IRIns *basea = refa, *baseb = refb;
  if (refa == refb && irt_sametype(xa->t, xb->t))
    return ALIAS_MUST;  /* Shortcut for same refs with identical type. */
  /* Offset-based disambiguation. */
  if (refa->o == IR_ADD && irref_isk(refa->op2)) {
    IRIns *irk = IR(refa->op2);
    basea = IR(refa->op1);
    ofsa = (LJ_64 && irk->o == IR_KINT64) ? (ptrdiff_t)ir_k64(irk)->u64 :
                                            (ptrdiff_t)irk->i;
  }
  if (refb->o == IR_ADD && irref_isk(refb->op2)) {
    IRIns *irk = IR(refb->op2);
    baseb = IR(refb->op1);
    ofsb = (LJ_64 && irk->o == IR_KINT64) ? (ptrdiff_t)ir_k64(irk)->u64 :
                                            (ptrdiff_t)irk->i;
  }
  /* Treat constified pointers like base vs. base+offset. */
  if (basea->o == IR_KPTR && baseb->o == IR_KPTR) {
    ofsb += (char *)ir_kptr(baseb) - (char *)ir_kptr(basea);
    baseb = basea;
  }
  /* This implements (very) strict aliasing rules.
  ** Different types do NOT alias, except for differences in signedness.
  ** Type punning through unions is allowed (but forces a reload).
  */
  if (basea == baseb) {
    ptrdiff_t sza = irt_size(xa->t), szb = irt_size(xb->t);
    if (ofsa == ofsb) {
      if (sza == szb && irt_isfp(xa->t) == irt_isfp(xb->t))
        return ALIAS_MUST;  /* Same-sized, same-kind. May need to convert. */
    } else if (ofsa + sza <= ofsb || ofsb + szb <= ofsa) {
      return ALIAS_NO;  /* Non-overlapping base+-o1 vs. base+-o2. */
    }
    /* NYI: extract, extend or reinterpret bits (int <-> fp). */
    return ALIAS_MAY;  /* Overlapping or type punning: force reload. */
  }
  if (!irt_sametype(xa->t, xb->t) &&
      !(irt_typerange(xa->t, IRT_I8, IRT_U64) &&
        ((xa->t.irt - IRT_I8) ^ (xb->t.irt - IRT_I8)) == 1))
    return ALIAS_NO;
  /* NYI: structural disambiguation. */
  return aa_cnew(J, basea, baseb);  /* Try to disambiguate allocations. */
}

/* Return CSEd reference or 0. Caveat: swaps lower ref to the right! */
static IRRef reassoc_trycse(jit_State *J, IROp op, IRRef op1, IRRef op2)
{
  IRRef ref = J->chain[op];
  IRRef lim = op1;
  if (op2 > lim) { lim = op2; op2 = op1; op1 = lim; }
  while (ref > lim) {
    IRIns *ir = IR(ref);
    if (ir->op1 == op1 && ir->op2 == op2)
      return ref;
    ref = ir->prev;
  }
  return 0;
}

/* Reassociate index references. */
static IRRef reassoc_xref(jit_State *J, IRIns *ir)
{
  ptrdiff_t ofs = 0;
  if (ir->o == IR_ADD && irref_isk(ir->op2)) {  /* Get constant offset. */
    IRIns *irk = IR(ir->op2);
    ofs = (LJ_64 && irk->o == IR_KINT64) ? (ptrdiff_t)ir_k64(irk)->u64 :
                                           (ptrdiff_t)irk->i;
    ir = IR(ir->op1);
  }
  if (ir->o == IR_ADD) {  /* Add of base + index. */
    /* Index ref > base ref for loop-carried dependences. Only check op1. */
    IRIns *ir2, *ir1 = IR(ir->op1);
    int32_t shift = 0;
    IRRef idxref;
    /* Determine index shifts. Don't bother with IR_MUL here. */
    if (ir1->o == IR_BSHL && irref_isk(ir1->op2))
      shift = IR(ir1->op2)->i;
    else if (ir1->o == IR_ADD && ir1->op1 == ir1->op2)
      shift = 1;
    else
      ir1 = ir;
    ir2 = IR(ir1->op1);
    /* A non-reassociated add. Must be a loop-carried dependence. */
    if (ir2->o == IR_ADD && irt_isint(ir2->t) && irref_isk(ir2->op2))
      ofs += (ptrdiff_t)IR(ir2->op2)->i << shift;
    else
      return 0;
    idxref = ir2->op1;
    /* Try to CSE the reassociated chain. Give up if not found. */
    if (ir1 != ir &&
        !(idxref = reassoc_trycse(J, ir1->o, idxref,
                                  ir1->o == IR_BSHL ? ir1->op2 : idxref)))
      return 0;
    if (!(idxref = reassoc_trycse(J, IR_ADD, idxref, ir->op2)))
      return 0;
    if (ofs != 0) {
      IRRef refk = tref_ref(lj_ir_kintp(J, ofs));
      if (!(idxref = reassoc_trycse(J, IR_ADD, idxref, refk)))
        return 0;
    }
    return idxref;  /* Success, found a reassociated index reference. Phew. */
  }
  return 0;  /* Failure. */
}

/* XLOAD forwarding. */
TRef LJ_FASTCALL lj_opt_fwd_xload(jit_State *J)
{
  IRRef xref = fins->op1;
  IRIns *xr = IR(xref);
  IRRef lim = xref;  /* Search limit. */
  IRRef ref;

  if ((fins->op2 & IRXLOAD_READONLY))
    goto cselim;
  if ((fins->op2 & IRXLOAD_VOLATILE))
    goto doemit;

  /* Search for conflicting stores. */
  ref = J->chain[IR_XSTORE];
retry:
  if (J->chain[IR_CALLXS] > lim) lim = J->chain[IR_CALLXS];
  if (J->chain[IR_XBAR] > lim) lim = J->chain[IR_XBAR];
  while (ref > lim) {
    IRIns *store = IR(ref);
    switch (aa_xref(J, xr, fins, store)) {
    case ALIAS_NO:   break;  /* Continue searching. */
    case ALIAS_MAY:  lim = ref; goto cselim;  /* Limit search for load. */
    case ALIAS_MUST:
      /* Emit conversion if the loaded type doesn't match the forwarded type. */
      if (!irt_sametype(fins->t, IR(store->op2)->t)) {
        IRType dt = irt_type(fins->t), st = irt_type(IR(store->op2)->t);
        if (dt == IRT_I8 || dt == IRT_I16) {  /* Trunc + sign-extend. */
          st = dt | IRCONV_SEXT;
          dt = IRT_INT;
        } else if (dt == IRT_U8 || dt == IRT_U16) {  /* Trunc + zero-extend. */
          st = dt;
          dt = IRT_INT;
        }
        fins->ot = IRT(IR_CONV, dt);
        fins->op1 = store->op2;
        fins->op2 = (dt<<5)|st;
        return RETRYFOLD;
      }
      return store->op2;  /* Store forwarding. */
    }
    ref = store->prev;
  }

cselim:
  /* Try to find a matching load. Below the conflicting store, if any. */
  ref = J->chain[IR_XLOAD];
  while (ref > lim) {
    /* CSE for XLOAD depends on the type, but not on the IRXLOAD_* flags. */
    if (IR(ref)->op1 == xref && irt_sametype(IR(ref)->t, fins->t))
      return ref;
    ref = IR(ref)->prev;
  }

  /* Reassociate XLOAD across PHIs to handle a[i-1] forwarding case. */
  if (!(fins->op2 & IRXLOAD_READONLY) && J->chain[IR_LOOP] &&
      xref == fins->op1 && (xref = reassoc_xref(J, xr)) != 0) {
    ref = J->chain[IR_XSTORE];
    while (ref > lim)  /* Skip stores that have already been checked. */
      ref = IR(ref)->prev;
    lim = xref;
    xr = IR(xref);
    goto retry;  /* Retry with the reassociated reference. */
  }
doemit:
  return EMITFOLD;
}

/* XSTORE elimination. */
TRef LJ_FASTCALL lj_opt_dse_xstore(jit_State *J)
{
  IRRef xref = fins->op1;
  IRIns *xr = IR(xref);
  IRRef lim = xref;  /* Search limit. */
  IRRef val = fins->op2;  /* Stored value reference. */
  IRRef1 *refp = &J->chain[IR_XSTORE];
  IRRef ref = *refp;
  if (J->chain[IR_CALLXS] > lim) lim = J->chain[IR_CALLXS];
  if (J->chain[IR_XBAR] > lim) lim = J->chain[IR_XBAR];
  if (J->chain[IR_XSNEW] > lim) lim = J->chain[IR_XSNEW];
  while (ref > lim) {  /* Search for redundant or conflicting stores. */
    IRIns *store = IR(ref);
    switch (aa_xref(J, xr, fins, store)) {
    case ALIAS_NO:
      break;  /* Continue searching. */
    case ALIAS_MAY:
      if (store->op2 != val)  /* Conflict if the value is different. */
        goto doemit;
      break;  /* Otherwise continue searching. */
    case ALIAS_MUST:
      if (store->op2 == val)  /* Same value: drop the new store. */
        return DROPFOLD;
      /* Different value: try to eliminate the redundant store. */
      if (ref > J->chain[IR_LOOP]) {  /* Quick check to avoid crossing LOOP. */
        IRIns *ir;
        /* Check for any intervening guards or any XLOADs (no AA performed). */
        for (ir = IR(J->cur.nins-1); ir > store; ir--)
          if (irt_isguard(ir->t) || ir->o == IR_XLOAD)
            goto doemit;  /* No elimination possible. */
        /* Remove redundant store from chain and replace with NOP. */
        *refp = store->prev;
        store->o = IR_NOP;
        store->t.irt = IRT_NIL;
        store->op1 = store->op2 = 0;
        store->prev = 0;
        /* Now emit the new store instead. */
      }
      goto doemit;
    }
    ref = *(refp = &store->prev);
  }
doemit:
  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
}

/* -- Forwarding of lj_tab_len -------------------------------------------- */

/* This is rather simplistic right now, but better than nothing. */
TRef LJ_FASTCALL lj_opt_fwd_tab_len(jit_State *J)
{
  IRRef tab = fins->op1;  /* Table reference. */
  IRRef lim = tab;  /* Search limit. */
  IRRef ref;

  /* Any ASTORE is a conflict and limits the search. */
  if (J->chain[IR_ASTORE] > lim) lim = J->chain[IR_ASTORE];

  /* Search for conflicting HSTORE with numeric key. */
  ref = J->chain[IR_HSTORE];
  while (ref > lim) {
    IRIns *store = IR(ref);
    IRIns *href = IR(store->op1);
    IRIns *key = IR(href->op2);
    if (irt_isnum(key->o == IR_KSLOT ? IR(key->op1)->t : key->t)) {
      lim = ref;  /* Conflicting store found, limits search for TLEN. */
      break;
    }
    ref = store->prev;
  }

  /* Search for aliasing table.clear. */
  if (!fwd_aa_tab_clear(J, lim, tab))
    return lj_ir_emit(J);

  /* Try to find a matching load. Below the conflicting store, if any. */
  return lj_opt_cselim(J, lim);
}

/* -- ASTORE/HSTORE previous type analysis -------------------------------- */

/* Check whether the previous value for a table store is non-nil.
** This can be derived either from a previous store or from a previous
** load (because all loads from tables perform a type check).
**
** The result of the analysis can be used to avoid the metatable check
** and the guard against HREF returning niltv. Both of these are cheap,
** so let's not spend too much effort on the analysis.
**
** A result of 1 is exact: previous value CANNOT be nil.
** A result of 0 is inexact: previous value MAY be nil.
*/
int lj_opt_fwd_wasnonnil(jit_State *J, IROpT loadop, IRRef xref)
{
  /* First check stores. */
  IRRef ref = J->chain[loadop+IRDELTA_L2S];
  while (ref > xref) {
    IRIns *store = IR(ref);
    if (store->op1 == xref) {  /* Same xREF. */
      /* A nil store MAY alias, but a non-nil store MUST alias. */
      return !irt_isnil(store->t);
    } else if (irt_isnil(store->t)) {  /* Must check any nil store. */
      IRRef skref = IR(store->op1)->op2;
      IRRef xkref = IR(xref)->op2;
      /* Same key type MAY alias. Need ALOAD check due to multiple int types. */
      if (loadop == IR_ALOAD || irt_sametype(IR(skref)->t, IR(xkref)->t)) {
        if (skref == xkref || !irref_isk(skref) || !irref_isk(xkref))
          return 0;  /* A nil store with same const key or var key MAY alias. */
        /* Different const keys CANNOT alias. */
      }  /* Different key types CANNOT alias. */
    }  /* Other non-nil stores MAY alias. */
    ref = store->prev;
  }

  /* Check loads since nothing could be derived from stores. */
  ref = J->chain[loadop];
  while (ref > xref) {
    IRIns *load = IR(ref);
    if (load->op1 == xref) {  /* Same xREF. */
      /* A nil load MAY alias, but a non-nil load MUST alias. */
      return !irt_isnil(load->t);
    }  /* Other non-nil loads MAY alias. */
    ref = load->prev;
  }
  return 0;  /* Nothing derived at all, previous value MAY be nil. */
}

/* ------------------------------------------------------------------------ */

#undef IR
#undef fins
#undef fleft
#undef fright

#endif

tarantool / luajit / 6482677868

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