[InstCombine] Optimize subtract of selects into a select of a sub

This came up when examining some code generated by clang's IRGen for
certain member pointers.

llvm-svn: 240369

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index c76d8d0e220..b1c7b7245cf 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -550,3 +550,25 @@ define i32 @test46(i32 %x, i32 %y) {
 ; CHECK-NEXT: %sub = and i32 %y, %x.not
 ; CHECK: ret i32 %sub
 }
+
+define i32 @test47(i1 %A, i32 %B, i32 %C, i32 %D) {
+  %sel0 = select i1 %A, i32 %D, i32 %B
+  %sel1 = select i1 %A, i32 %C, i32 %B
+  %sub = sub i32 %sel0, %sel1
+  ret i32 %sub
+; CHECK-LABEL: @test47(
+; CHECK-NEXT: %[[sub:.*]] = sub i32 %D, %C
+; CHECK-NEXT: %[[sel:.*]] = select i1 %A, i32 %[[sub]], i32 0
+; CHECK-NEXT: ret i32 %[[sel]]
+}
+
+define i32 @test48(i1 %A, i32 %B, i32 %C, i32 %D) {
+  %sel0 = select i1 %A, i32 %B, i32 %D
+  %sel1 = select i1 %A, i32 %B, i32 %C
+  %sub = sub i32 %sel0, %sel1
+  ret i32 %sub
+; CHECK-LABEL: @test48(
+; CHECK-NEXT: %[[sub:.*]] = sub i32 %D, %C
+; CHECK-NEXT: %[[sel:.*]] = select i1 %A, i32 0, i32 %[[sub]]
+; CHECK-NEXT: ret i32 %[[sel]]
+}