X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FInstructionSimplify.cpp;h=87125191ad0e77f429e177add08af6e2148b9ce6;hb=ed58a6f96f605901adc0df3ca76499d52b2d1a1a;hp=97612f46d327aac2059067141f1c999af6ce5b57;hpb=87689cfc54993959adb20b89a56bc58aad18ca56;p=oota-llvm.git

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 97612f46d32..87125191ad0 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -8,8 +8,10 @@
 //===----------------------------------------------------------------------===//
 //
 // This file implements routines for folding instructions into simpler forms
-// that do not require creating new instructions.  For example, this does
-// constant folding, and can handle identities like (X&0)->0.
+// that do not require creating new instructions.  This does constant folding
+// ("add i32 1, 1" -> "2") but can also handle non-constant operands, either
+// returning a constant ("and i32 %x, 0" -> "0") or an already existing value
+// ("and i32 %x, %x" -> "%x").
 //
 //===----------------------------------------------------------------------===//
 
@@ -18,6 +20,7 @@
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Support/PatternMatch.h"
 #include "llvm/Support/ValueHandle.h"
+#include "llvm/Target/TargetData.h"
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
@@ -295,7 +298,7 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
     return Op0;
 
   // A & ~A  =  ~A & A  =  0
-  Value *A, *B;
+  Value *A = 0, *B = 0;
   if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
       (match(Op1, m_Not(m_Value(A))) && A == Op0))
     return Constant::getNullValue(Op0->getType());
@@ -374,7 +377,7 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
     return Op1;
 
   // A | ~A  =  ~A | A  =  -1
-  Value *A, *B;
+  Value *A = 0, *B = 0;
   if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
       (match(Op1, m_Not(m_Value(A))) && A == Op0))
     return Constant::getAllOnesValue(Op0->getType());
@@ -449,7 +452,7 @@ static Value *SimplifyXorInst(Value *Op0, Value *Op1, const TargetData *TD,
     return Constant::getNullValue(Op0->getType());
 
   // A ^ ~A  =  ~A ^ A  =  -1
-  Value *A, *B;
+  Value *A = 0, *B = 0;
   if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
       (match(Op1, m_Not(m_Value(A))) && A == Op0))
     return Constant::getAllOnesValue(Op0->getType());
@@ -690,19 +693,33 @@ Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
 /// fold the result.  If not, this returns null.
 Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
                              const TargetData *TD, const DominatorTree *) {
+  // The type of the GEP pointer operand.
+  const PointerType *PtrTy = cast<PointerType>(Ops[0]->getType());
+
   // getelementptr P -> P.
   if (NumOps == 1)
     return Ops[0];
 
-  // TODO.
-  //if (isa<UndefValue>(Ops[0]))
-  //  return UndefValue::get(GEP.getType());
+  if (isa<UndefValue>(Ops[0])) {
+    // Compute the (pointer) type returned by the GEP instruction.
+    const Type *LastType = GetElementPtrInst::getIndexedType(PtrTy, &Ops[1],
+                                                             NumOps-1);
+    const Type *GEPTy = PointerType::get(LastType, PtrTy->getAddressSpace());
+    return UndefValue::get(GEPTy);
+  }
 
-  // getelementptr P, 0 -> P.
-  if (NumOps == 2)
+  if (NumOps == 2) {
+    // getelementptr P, 0 -> P.
     if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
       if (C->isZero())
         return Ops[0];
+    // getelementptr P, N -> P if P points to a type of zero size.
+    if (TD) {
+      const Type *Ty = PtrTy->getElementType();
+      if (Ty->isSized() && TD->getTypeAllocSize(Ty) == 0)
+        return Ops[0];
+    }
+  }
 
   // Check to see if this is constant foldable.
   for (unsigned i = 0; i != NumOps; ++i)