JIT: Fix bad constant folding of (0 shift x) => x (#113493)

jakobbotsch · web-flow · commit e4da0a1ae94a · 2025-03-14T21:10:26.000+01:00
diff --git a/src/coreclr/jit/lower.cpp b/src/coreclr/jit/lower.cpp
@@ -7810,10 +7810,10 @@ bool Lowering::TryFoldBinop(GenTreeOp* node)
         return true;
     }
 
-    if (node->OperIs(GT_LSH, GT_RSH, GT_RSZ, GT_ROL, GT_ROR, GT_OR, GT_XOR) &&
-        (op1->IsIntegralConst(0) || op2->IsIntegralConst(0)))
+    if ((node->OperIs(GT_LSH, GT_RSH, GT_RSZ, GT_ROL, GT_ROR) && op2->IsIntegralConst(0)) ||
+        (node->OperIs(GT_OR, GT_XOR) && (op1->IsIntegralConst(0) || op2->IsIntegralConst(0))))
     {
-        GenTree* zeroOp  = op1->IsIntegralConst(0) ? op1 : op2;
+        GenTree* zeroOp  = op2->IsIntegralConst(0) ? op2 : op1;
         GenTree* otherOp = zeroOp == op1 ? op2 : op1;
 
         LIR::Use use;

Original file line number	Diff line number	Diff line change
`@@ -7810,10 +7810,10 @@ bool Lowering::TryFoldBinop(GenTreeOp* node)`
`7810`	`7810`	`return true;`
`7811`	`7811`	`}`
`7812`	`7812`
`7813`		`- if (node->OperIs(GT_LSH, GT_RSH, GT_RSZ, GT_ROL, GT_ROR, GT_OR, GT_XOR) &&`
`7814`		`- (op1->IsIntegralConst(0) \|\| op2->IsIntegralConst(0)))`
	`7813`	`+ if ((node->OperIs(GT_LSH, GT_RSH, GT_RSZ, GT_ROL, GT_ROR) && op2->IsIntegralConst(0)) \|\|`
	`7814`	`+ (node->OperIs(GT_OR, GT_XOR) && (op1->IsIntegralConst(0) \|\| op2->IsIntegralConst(0))))`
`7815`	`7815`	`{`
`7816`		`- GenTree* zeroOp = op1->IsIntegralConst(0) ? op1 : op2;`
	`7816`	`+ GenTree* zeroOp = op2->IsIntegralConst(0) ? op2 : op1;`
`7817`	`7817`	`GenTree* otherOp = zeroOp == op1 ? op2 : op1;`
`7818`	`7818`
`7819`	`7819`	`LIR::Use use;`