Add an instcombine for constructs like a | -(b != c); a select is more

canonical, and generally leads to better code.  Found while looking at
an article about saturating arithmetic.

llvm-svn: 129545

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 1cb18e12eef..6cf405328a3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2003,7 +2003,14 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
       }
     }
   }
-  
+
+  // or(sext(A), B) -> A ? -1 : B where A is an i1
+  // or(A, sext(B)) -> B ? -1 : A where B is an i1
+  if (match(Op0, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
+    return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op1);
+  if (match(Op1, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
+    return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op0);
+
   // Note: If we've gotten to the point of visiting the outer OR, then the
   // inner one couldn't be simplified.  If it was a constant, then it won't
   // be simplified by a later pass either, so we try swapping the inner/outer