Fold ashr -1, X into -1

llvm-svn: 4070
2002-10-08 16:16:40 +00:00 · 2002-10-08 16:16:40 +00:00 · 2e0fb39d87
parent ee5c8a9e8d
commit 2e0fb39d87
1 changed files with 6 additions and 0 deletions
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@ -503,6 +503,12 @@ Instruction *InstCombiner::visitShiftInst(Instruction &I) {
      return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());

  }
+
+  // shr int -1, X = -1   (for any arithmetic shift rights of ~0)
+  if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
+    if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
+      return ReplaceInstUsesWith(I, CSI);
+  
  return 0;
 }