From de7f1c9a63eca3f46538302c1feed6219225707f Mon Sep 17 00:00:00 2001
From: Robert Bocchino <bocchino@illinois.edu>
Date: Tue, 10 Jan 2006 20:03:46 +0000
Subject: [PATCH] Added constant folding support for the extractelement
 operation.

llvm-svn: 25187
---
 llvm/lib/VMCore/ConstantFolding.cpp | 10 ++++++++++
 llvm/lib/VMCore/ConstantFolding.h   |  2 ++
 llvm/lib/VMCore/Constants.cpp       |  2 ++
 3 files changed, 14 insertions(+)

diff --git a/llvm/lib/VMCore/ConstantFolding.cpp b/llvm/lib/VMCore/ConstantFolding.cpp
index 40a51cc8901b..3f7bc7db33a9 100644
--- a/llvm/lib/VMCore/ConstantFolding.cpp
+++ b/llvm/lib/VMCore/ConstantFolding.cpp
@@ -724,6 +724,16 @@ Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond,
   return 0;
 }
 
+Constant *llvm::ConstantFoldExtractElementInstruction(const Constant *Val,
+                                                      const Constant *Idx) {
+  if (const ConstantPacked *CVal = dyn_cast<ConstantPacked>(Val)) {
+    if (const ConstantUInt *CIdx = dyn_cast<ConstantUInt>(Idx)) {
+      return const_cast<Constant*>(CVal->getOperand(CIdx->getValue()));
+    }
+  } 
+  return 0;
+}
+
 /// isZeroSizedType - This type is zero sized if its an array or structure of
 /// zero sized types.  The only leaf zero sized type is an empty structure.
 static bool isMaybeZeroSizedType(const Type *Ty) {
diff --git a/llvm/lib/VMCore/ConstantFolding.h b/llvm/lib/VMCore/ConstantFolding.h
index a864aa2cd80c..e8580c429051 100644
--- a/llvm/lib/VMCore/ConstantFolding.h
+++ b/llvm/lib/VMCore/ConstantFolding.h
@@ -31,6 +31,8 @@ namespace llvm {
   Constant *ConstantFoldSelectInstruction(const Constant *Cond,
                                           const Constant *V1,
                                           const Constant *V2);
+  Constant *ConstantFoldExtractElementInstruction(const Constant *Val,
+                                                  const Constant *Idx);
   Constant *ConstantFoldBinaryInstruction(unsigned Opcode, const Constant *V1,
                                           const Constant *V2);
   Constant *ConstantFoldGetElementPtr(const Constant *C,
diff --git a/llvm/lib/VMCore/Constants.cpp b/llvm/lib/VMCore/Constants.cpp
index 610ed784c89a..f4ff31f24f21 100644
--- a/llvm/lib/VMCore/Constants.cpp
+++ b/llvm/lib/VMCore/Constants.cpp
@@ -1403,6 +1403,8 @@ Constant *ConstantExpr::getGetElementPtr(Constant *C,
 
 Constant *ConstantExpr::getExtractElementTy(const Type *ReqTy, Constant *Val,
                                             Constant *Idx) {
+  if (Constant *FC = ConstantFoldExtractElementInstruction(Val, Idx))
+    return FC;          // Fold a few common cases...
   // Look up the constant in the table first to ensure uniqueness
   std::vector<Constant*> ArgVec(1, Val);
   ArgVec.push_back(Idx);