[InstCombine] Fold (xor (min/max X, Y), -1) -> (max/min ~X, ~Y) when X and Y are freely invertible.

This allows the xor to be removed completely.

This might help with recomitting r341674, but seems good regardless.

Coincidentally fixes PR38915.

Differential Revision: https://reviews.llvm.org/D51964

llvm-svn: 342163

2 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index a1a85339be6..898063871ac 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2898,6 +2898,17 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
         return SelectInst::Create(
             Builder.CreateICmp(getInverseMinMaxPred(SPF), NotX, Y), NotX, Y);
       }
+
+      // If both sides are freely invertible, then we can get rid of the xor
+      // completely.
+      if (IsFreeToInvert(LHS, !LHS->hasNUsesOrMore(3)) &&
+          IsFreeToInvert(RHS, !RHS->hasNUsesOrMore(3))) {
+        Value *NotLHS = Builder.CreateNot(LHS);
+        Value *NotRHS = Builder.CreateNot(RHS);
+        return SelectInst::Create(
+            Builder.CreateICmp(getInverseMinMaxPred(SPF), NotLHS, NotRHS),
+            NotLHS, NotRHS);
+      }
     }
   }
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index a388269d6e6..b7e237eb6ed 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1847,6 +1847,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       // MIN(~a, ~b) -> ~MAX(a, b)
       Value *A, *B;
       if (match(LHS, m_Not(m_Value(A))) && match(RHS, m_Not(m_Value(B))) &&
+          !IsFreeToInvert(A, A->hasOneUse()) &&
+          !IsFreeToInvert(B, B->hasOneUse()) &&
           (!LHS->hasNUsesOrMore(3) || !RHS->hasNUsesOrMore(3))) {
         CmpInst::Predicate InvertedPred = getInverseMinMaxPred(SPF);
         Value *InvertedCmp = Builder.CreateICmp(InvertedPred, A, B);