From 032742972f69c014dd5e985753c06a7fe3d08704 Mon Sep 17 00:00:00 2001
From: Bob Wilson <bob.wilson@apple.com>
Date: Mon, 25 Jan 2010 18:26:54 +0000
Subject: [PATCH] Change Value::getUnderlyingObject to have the MaxLookup value
 specified as a parameter with a default value, instead of just hardcoding it
 in the implementation.  The limit of MaxLookup = 6 was introduced in r69151
 to fix a performance problem with O(n^2) behavior in instcombine, but the
 scalarrepl pass is relying on getUnderlyingObject to go all the way back to
 an AllocaInst. Making the limit part of the method signature makes it clear
 that by default the result is limited and should help avoid similar problems
 in the future. This fixes pr6126.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94433 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Value.h                           | 9 +++++----
 lib/Transforms/Scalar/ScalarReplAggregates.cpp | 6 +++---
 lib/VMCore/Value.cpp                           | 7 +++----
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/llvm/Value.h b/include/llvm/Value.h
index f0bd8bea1ed..9045906e7be 100644
--- a/include/llvm/Value.h
+++ b/include/llvm/Value.h
@@ -285,10 +285,11 @@ public:
   /// getUnderlyingObject - This method strips off any GEP address adjustments
   /// and pointer casts from the specified value, returning the original object
   /// being addressed.  Note that the returned value has pointer type if the
-  /// specified value does.
-  Value *getUnderlyingObject();
-  const Value *getUnderlyingObject() const {
-    return const_cast<Value*>(this)->getUnderlyingObject();
+  /// specified value does.  If the MaxLookup value is non-zero, it limits the
+  /// number of instructions to be stripped off.
+  Value *getUnderlyingObject(unsigned MaxLookup = 6);
+  const Value *getUnderlyingObject(unsigned MaxLookup = 6) const {
+    return const_cast<Value*>(this)->getUnderlyingObject(MaxLookup);
   }
   
   /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
diff --git a/lib/Transforms/Scalar/ScalarReplAggregates.cpp b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
index f4734801e0f..1cf486bbdfa 100644
--- a/lib/Transforms/Scalar/ScalarReplAggregates.cpp
+++ b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -1384,9 +1384,9 @@ void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset) {
       // If the source and destination are both to the same alloca, then this is
       // a noop copy-to-self, just delete it.  Otherwise, emit a load and store
       // as appropriate.
-      AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject());
+      AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject(0));
       
-      if (MTI->getSource()->getUnderlyingObject() != OrigAI) {
+      if (MTI->getSource()->getUnderlyingObject(0) != OrigAI) {
         // Dest must be OrigAI, change this to be a load from the original
         // pointer (bitcasted), then a store to our new alloca.
         assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
@@ -1396,7 +1396,7 @@ void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset) {
         LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
         SrcVal->setAlignment(MTI->getAlignment());
         Builder.CreateStore(SrcVal, NewAI);
-      } else if (MTI->getDest()->getUnderlyingObject() != OrigAI) {
+      } else if (MTI->getDest()->getUnderlyingObject(0) != OrigAI) {
         // Src must be OrigAI, change this to be a load from NewAI then a store
         // through the original dest pointer (bitcasted).
         assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
diff --git a/lib/VMCore/Value.cpp b/lib/VMCore/Value.cpp
index 40679bfc290..3759b8a7cbb 100644
--- a/lib/VMCore/Value.cpp
+++ b/lib/VMCore/Value.cpp
@@ -341,12 +341,11 @@ Value *Value::stripPointerCasts() {
   } while (1);
 }
 
-Value *Value::getUnderlyingObject() {
+Value *Value::getUnderlyingObject(unsigned MaxLookup) {
   if (!isa<PointerType>(getType()))
     return this;
   Value *V = this;
-  unsigned MaxLookup = 6;
-  do {
+  for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
       V = GEP->getPointerOperand();
     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
@@ -359,7 +358,7 @@ Value *Value::getUnderlyingObject() {
       return V;
     }
     assert(isa<PointerType>(V->getType()) && "Unexpected operand type!");
-  } while (--MaxLookup);
+  }
   return V;
 }