[InstCombine] Support sext in foldLogicCastConstant

This adds support for sext in foldLogicCastConstant. This is a prerequisite for D36214.

Differential Revision: https://reviews.llvm.org/D36234

llvm-svn: 309880

1 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 9d68201fc7a..87678f3777c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1089,10 +1089,10 @@ static Instruction *foldLogicCastConstant(BinaryOperator &Logic, CastInst *Cast,
   Type *DestTy = Logic.getType();
   Type *SrcTy = Cast->getSrcTy();
 
-  // Move the logic operation ahead of a zext if the constant is unchanged in
-  // the smaller source type. Performing the logic in a smaller type may provide
-  // more information to later folds, and the smaller logic instruction may be
-  // cheaper (particularly in the case of vectors).
+  // Move the logic operation ahead of a zext or sext if the constant is
+  // unchanged in the smaller source type. Performing the logic in a smaller
+  // type may provide more information to later folds, and the smaller logic
+  // instruction may be cheaper (particularly in the case of vectors).
   Value *X;
   if (match(Cast, m_OneUse(m_ZExt(m_Value(X))))) {
     Constant *TruncC = ConstantExpr::getTrunc(C, SrcTy);
@@ -1104,6 +1104,16 @@ static Instruction *foldLogicCastConstant(BinaryOperator &Logic, CastInst *Cast,
     }
   }
 
+  if (match(Cast, m_OneUse(m_SExt(m_Value(X))))) {
+    Constant *TruncC = ConstantExpr::getTrunc(C, SrcTy);
+    Constant *SextTruncC = ConstantExpr::getSExt(TruncC, DestTy);
+    if (SextTruncC == C) {
+      // LogicOpc (sext X), C --> sext (LogicOpc X, C)
+      Value *NewOp = Builder.CreateBinOp(LogicOpc, X, TruncC);
+      return new SExtInst(NewOp, DestTy);
+    }
+  }
+
   return nullptr;
 }