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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181668 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 20 insertions, 6 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 249407818f..87d56214a3 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/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;
 }
 
diff --git a/test/Transforms/InstCombine/rem.ll b/test/Transforms/InstCombine/rem.ll
index 9b8b98a170..450a62ae6d 100644
--- a/test/Transforms/InstCombine/rem.ll
+++ b/test/Transforms/InstCombine/rem.ll
@@ -135,3 +135,17 @@ define i64 @test14(i64 %x, i32 %y) {
 	%urem = urem i64 %x, %zext
 	ret i64 %urem
 }
+
+define i64 @test15(i32 %x, i32 %y) {
+; CHECK: @test15
+; CHECK-NEXT: [[SHL:%.*]] = shl nuw i32 1, %y
+; CHECK-NEXT: [[ADD:%.*]] = add i32 [[SHL]], -1
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[ADD]], %x
+; CHECK-NEXT: [[ZEXT:%.*]] = zext i32 [[AND]] to i64
+; CHECK-NEXT: ret i64 [[ZEXT]]
+	%shl = shl i32 1, %y
+	%zext0 = zext i32 %shl to i64
+	%zext1 = zext i32 %x to i64
+	%urem = urem i64 %zext1, %zext0
+	ret i64 %urem
+}