DUALNUM: Make overflow guards weak. Add IR_USE and IR_MULOV.

src/lj_asm.c

@@ -3992,6 +3992,8 @@ static void asm_ir(ASMState *as, IRIns *ir)
   /* Miscellaneous ops. */
   case IR_LOOP: asm_loop(as); break;
   case IR_NOP: case IR_XBAR: lua_assert(!ra_used(ir)); 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;
 
@@ -4077,6 +4079,7 @@ static void asm_ir(ASMState *as, IRIns *ir)
   /* Overflow-checking arithmetic ops. Note: don't use LEA here! */
   case IR_ADDOV: asm_intarith(as, ir, XOg_ADD); break;
   case IR_SUBOV: asm_intarith(as, ir, XOg_SUB); break;
+  case IR_MULOV: asm_intarith(as, ir, XOg_X_IMUL); break;
 
   /* Memory references. */
   case IR_AREF: asm_aref(as, ir); break;

src/lj_ir.h

@@ -35,6 +35,7 @@
   _(BASE,	N , lit, lit) \
   _(HIOP,	S , ref, ref) \
   _(LOOP,	S , ___, ___) \
+  _(USE,	S , ref, ___) \
   _(PHI,	S , ref, ref) \
   _(RENAME,	S , ref, lit) \
   \
@@ -78,8 +79,9 @@
   _(FPMATH,	N , ref, lit) \
   \
   /* Overflow-checking arithmetic ops. */ \
-  _(ADDOV,	C , ref, ref) \
-  _(SUBOV,	N , ref, ref) \
+  _(ADDOV,	CW, ref, ref) \
+  _(SUBOV,	NW, ref, ref) \
+  _(MULOV,	CW, ref, ref) \
   \
   /* Memory ops. A = array, H = hash, U = upvalue, F = field, S = stack. */ \
   \
@@ -339,6 +341,7 @@ typedef enum {
 #define IRM_W			0x80
 
 #define IRM_NW			(IRM_N|IRM_W)
+#define IRM_CW			(IRM_C|IRM_W)
 #define IRM_AW			(IRM_A|IRM_W)
 #define IRM_LW			(IRM_L|IRM_W)
 

src/lj_opt_fold.c

@@ -247,6 +247,19 @@ LJFOLDF(kfold_intarith)
   return INTFOLD(kfold_intop(fleft->i, fright->i, (IROp)fins->o));
 }
 
+LJFOLD(ADDOV KINT KINT)
+LJFOLD(SUBOV KINT KINT)
+LJFOLD(MULOV KINT KINT)
+LJFOLDF(kfold_intovarith)
+{
+  lua_Number n = lj_vm_foldarith((lua_Number)fleft->i, (lua_Number)fright->i,
+				 fins->o - IR_ADDOV);
+  int32_t k = lj_num2int(n);
+  if (n != (lua_Number)k)
+    return FAILFOLD;
+  return INTFOLD(k);
+}
+
 LJFOLD(BNOT KINT)
 LJFOLDF(kfold_bnot)
 {
@@ -992,6 +1005,21 @@ LJFOLDF(simplify_intadd_k)
   return NEXTFOLD;
 }
 
+LJFOLD(MULOV any KINT)
+LJFOLDF(simplify_intmul_k)
+{
+  if (fright->i == 0)  /* i * 0 ==> 0 */
+    return RIGHTFOLD;
+  if (fright->i == 1)  /* i * 1 ==> i */
+    return LEFTFOLD;
+  if (fright->i == 2) {  /* i * 2 ==> i + i */
+    fins->o = IR_ADDOV;
+    fins->op2 = fins->op1;
+    return RETRYFOLD;
+  }
+  return NEXTFOLD;
+}
+
 LJFOLD(SUB any KINT)
 LJFOLDF(simplify_intsub_k)
 {
@@ -1484,6 +1512,7 @@ LJFOLDF(abc_invar)
 LJFOLD(ADD any any)
 LJFOLD(MUL any any)
 LJFOLD(ADDOV any any)
+LJFOLD(MULOV any any)
 LJFOLDF(comm_swap)
 {
   if (fins->op1 < fins->op2) {  /* Move lower ref to the right. */

src/lj_record.c

@@ -1860,8 +1860,9 @@ static void rec_setup_forl(jit_State *J, const BCIns *fori)
 	    emitir(IRTGI(IR_GE), step, lj_ir_kint(J, (int32_t)0x80000000-k));
 	}
       } else {
-	/* Stop+step variable: need full overflow check (with dead result). */
-	emitir(IRTGI(IR_ADDOV), step, stop);
+	/* Stop+step variable: need full overflow check. */
+	TRef tr = emitir(IRTGI(IR_ADDOV), step, stop);
+	emitir(IRTI(IR_USE), tr, 0);  /* ADDOV is weak. Avoid dead result. */
       }
     }
   } else if (t == IRT_INT && !tref_isk(stop)) {