[InstCombine] canonicalize add/sub with bool

add A, sext(B) --> sub A, zext(B)

We have to choose 1 of these forms, so I'm opting for the
zext because that's easier for value tracking.

The backend should be prepared for this change after:
D57401
rL353433

This is also a preliminary step towards reducing the amount
of bit hackery that we do in IR to optimize icmp/select.
That should be waiting to happen at a later optimization stage.

The seeming regression in the fuzzer test was discussed in:
D58359

We were only managing that fold in instcombine by luck, and
other passes should be able to deal with that better anyway.

llvm-svn: 354748

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index bf92b5dc559..e2d4774b71f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1118,6 +1118,12 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
     return BinaryOperator::CreateSub(RHS, A);
   }
 
+  // Canonicalize sext to zext for better value tracking potential.
+  // add A, sext(B) --> sub A, zext(B)
+  if (match(&I, m_c_Add(m_Value(A), m_OneUse(m_SExt(m_Value(B))))) &&
+      B->getType()->isIntOrIntVectorTy(1))
+    return BinaryOperator::CreateSub(A, Builder.CreateZExt(B, Ty));
+
   // A + -B  -->  A - B
   if (match(RHS, m_Neg(m_Value(B))))
     return BinaryOperator::CreateSub(LHS, B);