[InstCombine] Add new combine to add folding

(X | C1) + C2 --> (X | C1) ^ C1 iff (C1 == -C2)

I verified the correctness using Alive:
https://rise4fun.com/Alive/YNV

This transform enables the following transform that already exists in
instcombine:

(X | Y) ^ Y --> X & ~Y

As a result, the full expected transform is:

(X | C1) + C2 --> X & ~C1 iff (C1 == -C2)

There already exists the transform in the sub case:

(X | Y) - Y --> X & ~Y

However this does not trigger in the case where Y is constant due to an earlier
transform:

X - (-C) --> X + C

With this new add fold, both the add and sub constant cases are handled.

Patch by Chris Dawson.

Differential Revision: https://reviews.llvm.org/D61517

llvm-svn: 360185

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/test/Transforms/InstCombine/with_overflow.ll b/llvm/test/Transforms/InstCombine/with_overflow.ll
index e80da2afe2f..b15e37ce6e0 100644
--- a/llvm/test/Transforms/InstCombine/with_overflow.ll
+++ b/llvm/test/Transforms/InstCombine/with_overflow.ll
@@ -531,10 +531,9 @@ define { i32, i1 } @umul_canonicalize_constant_arg0(i32 %x) nounwind {
 
 define { i8, i1 } @uadd_always_overflow(i8 %x) nounwind {
 ; CHECK-LABEL: @uadd_always_overflow(
-; CHECK-NEXT:    [[Y:%.*]] = or i8 [[X:%.*]], -64
-; CHECK-NEXT:    [[A:%.*]] = add nsw i8 [[Y]], 64
-; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[A]], 0
-; CHECK-NEXT:    ret { i8, i1 } [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 63
+; CHECK-NEXT:    [[TMP2:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[TMP1]], 0
+; CHECK-NEXT:    ret { i8, i1 } [[TMP2]]
 ;
   %y = or i8 %x, 192
   %a = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 %y, i8 64)