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, 14 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
index 9b8b98a1708..450a62ae6de 100644
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/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
+}