InstCombine: Flip the order of two urem transforms

There are two transforms in visitUrem that conflict with each other.

*) One, if a divisor is a power of two, subtracts one from the divisor
   and turns it into a bitwise-and.
*) The other unwraps both operands if they are surrounded by zext
   instructions.

Flipping the order allows the subtraction to go beneath the sign
extension.

llvm-svn: 181668

1 files changed, 6 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 249407818fd..87d56214a36 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1027,6 +1027,12 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
   if (Instruction *common = commonIRemTransforms(I))
     return common;
 
+  // (zext A) urem (zext B) --> zext (A urem B)
+  if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
+    if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
+      return new ZExtInst(Builder->CreateURem(ZOp0->getOperand(0), ZOp1),
+                          I.getType());
+
   // X urem Y -> X and Y-1, where Y is a power of 2,
   if (isKnownToBeAPowerOfTwo(Op1, /*OrZero*/true)) {
     Constant *N1 = Constant::getAllOnesValue(I.getType());
@@ -1034,12 +1040,6 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
     return BinaryOperator::CreateAnd(Op0, Add);
   }
 
-  // (zext A) urem (zext B) --> zext (A urem B)
-  if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
-    if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
-      return new ZExtInst(Builder->CreateURem(ZOp0->getOperand(0), ZOp1),
-                          I.getType());
-
   return 0;
 }