--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/luajit/src/lj_opt_mem.c	Fri Jan 23 22:38:59 2026 -0800
@@ -0,0 +1,985 @@
+/*
+** Memory access optimizations.
+** AA: Alias Analysis using high-level semantic disambiguation.
+** FWD: Load Forwarding (L2L) + Store Forwarding (S2L).
+** DSE: Dead-Store Elimination.
+** Copyright (C) 2005-2023 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);
+}
+
+/* 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);
+}
+
+/* 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))) &&
+	fwd_aa_tab_clear(J, tab, tab)) {
+      /* 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 && fwd_aa_tab_clear(J, ref, tab))
+	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 && fwd_aa_tab_clear(J, tab, tab))
+    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. */
+}
+
+/* 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).
+	** Note that lj_tab_keyindex and lj_vm_next don't need guards,
+	** since they are followed by at least one guarded VLOAD.
+	*/
+	for (ir = IR(J->cur.nins-1); ir > store; ir--)
+	  if (irt_isguard(ir->t) || ir->o == IR_ALEN)
+	    goto doemit;  /* No elimination possible. */
+	/* Remove redundant store from chain and replace with NOP. */
+	*refp = store->prev;
+	lj_ir_nop(store);
+	/* Now emit the new store instead. */
+      }
+      goto doemit;
+    }
+    ref = *(refp = &store->prev);
+  }
+doemit:
+  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
+}
+
+/* ALEN forwarding. */
+TRef LJ_FASTCALL lj_opt_fwd_alen(jit_State *J)
+{
+  IRRef tab = fins->op1;  /* Table reference. */
+  IRRef lim = tab;  /* Search limit. */
+  IRRef ref;
+
+  /* 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 ALEN. */
+      break;
+    }
+    ref = store->prev;
+  }
+
+  /* Try to find a matching ALEN. */
+  ref = J->chain[IR_ALEN];
+  while (ref > lim) {
+    /* CSE for ALEN only depends on the table, not the hint. */
+    if (IR(ref)->op1 == tab) {
+      IRRef sref;
+
+      /* Search for aliasing table.clear. */
+      if (!fwd_aa_tab_clear(J, ref, tab))
+	break;
+
+      /* Search for hint-forwarding or conflicting store. */
+      sref = J->chain[IR_ASTORE];
+      while (sref > ref) {
+	IRIns *store = IR(sref);
+	IRIns *aref = IR(store->op1);
+	IRIns *fref = IR(aref->op1);
+	if (tab == fref->op1) {  /* ASTORE to the same table. */
+	  /* Detect t[#t+1] = x idiom for push. */
+	  IRIns *idx = IR(aref->op2);
+	  if (!irt_isnil(store->t) &&
+	      idx->o == IR_ADD && idx->op1 == ref &&
+	      IR(idx->op2)->o == IR_KINT && IR(idx->op2)->i == 1) {
+	    /* Note: this requires an extra PHI check in loop unroll. */
+	    fins->op2 = aref->op2;  /* Set ALEN hint. */
+	  }
+	  goto doemit;  /* Conflicting store, possibly giving a hint. */
+	} else if (aa_table(J, tab, fref->op1) != ALIAS_NO) {
+	  goto doemit;  /* Conflicting store. */
+	}
+	sref = store->prev;
+      }
+
+      return ref;  /* Plain ALEN forwarding. */
+    }
+    ref = IR(ref)->prev;
+  }
+doemit:
+  return EMITFOLD;
+}
+
+/* -- 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;
+	lj_ir_nop(store);
+	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;
+	  lj_ir_nop(obar);
+	}
+	/* 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 &&
+	  !(xr->op2 >= IRFL_SBUF_W && xr->op2 <= IRFL_SBUF_R))
+	return DROPFOLD;  /* Same value: drop the new store. */
+      /* 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;
+	lj_ir_nop(store);
+	/* Now emit the new store instead. */
+      }
+      goto doemit;
+    }
+    ref = *(refp = &store->prev);
+  }
+doemit:
+  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
+}
+
+/* Check whether there's no aliasing buffer op between IRFL_SBUF_*. */
+int LJ_FASTCALL lj_opt_fwd_sbuf(jit_State *J, IRRef lim)
+{
+  IRRef ref;
+  if (J->chain[IR_BUFPUT] > lim)
+    return 0;  /* Conflict. */
+  ref = J->chain[IR_CALLS];
+  while (ref > lim) {
+    IRIns *ir = IR(ref);
+    if (ir->op2 >= IRCALL_lj_strfmt_putint && ir->op2 < IRCALL_lj_buf_tostr)
+      return 0;  /* Conflict. */
+    ref = ir->prev;
+  }
+  ref = J->chain[IR_CALLL];
+  while (ref > lim) {
+    IRIns *ir = IR(ref);
+    if (ir->op2 >= IRCALL_lj_strfmt_putint && ir->op2 < IRCALL_lj_buf_tostr)
+      return 0;  /* Conflict. */
+    ref = ir->prev;
+  }
+  return 1;  /* No conflict. Can safely FOLD/CSE. */
+}
+
+/* -- 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;
+	lj_ir_nop(store);
+	/* Now emit the new store instead. */
+      }
+      goto doemit;
+    }
+    ref = *(refp = &store->prev);
+  }
+doemit:
+  return EMITFOLD;  /* Otherwise we have a conflict or simply no match. */
+}
+
+/* -- 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