From: Chris Lattner <sabre@nondot.org>
Date: Fri, 31 Mar 2006 18:31:40 +0000 (+0000)
Subject: constant fold extractelement with undef operands.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=6fa4cdf92eb240f06c7705a8d72b408668b5869b;p=oota-llvm.git

constant fold extractelement with undef operands.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27301 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index a6fbf42fa24..ee5ee0ee42c 100644
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -726,11 +726,17 @@ Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond,
 
 Constant *llvm::ConstantFoldExtractElementInstruction(const Constant *Val,
                                                       const Constant *Idx) {
+  if (isa<UndefValue>(Val))  // ee(undef, x) -> undef
+    return UndefValue::get(cast<PackedType>(Val->getType())->getElementType());
+  
   if (const ConstantPacked *CVal = dyn_cast<ConstantPacked>(Val)) {
     if (const ConstantUInt *CIdx = dyn_cast<ConstantUInt>(Idx)) {
       return const_cast<Constant*>(CVal->getOperand(CIdx->getValue()));
+    } else if (isa<UndefValue>(Idx)) {
+      // ee({w,x,y,z}, undef) -> w (an arbitrary value).
+      return const_cast<Constant*>(CVal->getOperand(0));
     }
-  } 
+  }
   return 0;
 }