[InstCombine] Support (sub (sext x), (sext y)) --> (sext (sub x, y)) and (sub (zext x), (zext y)) --> (zext (sub x, y))
Summary:
If the sub doesn't overflow in the original type we can move it above the sext/zext.
This is similar to what we do for add. The overflow checking for sub is currently weaker than add, so the test cases are constructed for what is supported.
Reviewers: spatel
Reviewed By: spatel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D52075
llvm-svn: 342335
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index acb62b6..910ec83 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1697,6 +1697,9 @@
return SelectInst::Create(Cmp, Neg, A);
}
+ if (Instruction *Ext = narrowMathIfNoOverflow(I))
+ return Ext;
+
bool Changed = false;
if (!I.hasNoSignedWrap() && willNotOverflowSignedSub(Op0, Op1, I)) {
Changed = true;