From 42cb684f8d8440ffd79415280dcb7676d0b5f29a Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Tue, 30 Nov 2010 21:38:30 +0000
Subject: [PATCH] two improvements to RemoveAccessedObjects: 1. if the
 underlying pointer passed in can be resolved    to any argument or alloca,
 then we don't need to scan.    Previously we would only avoid the scan if the
 alloca    or byval was actually considered dead. 2. The dead store processing
 code is itself completely    dead and didn't handle volatile stores right
 anyway,    so delete it.  This allows simplifying the interface    to
 RemoveAccessedObjects.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120467 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Scalar/DeadStoreElimination.cpp           | 35 ++++---------------
 1 file changed, 7 insertions(+), 28 deletions(-)

diff --git a/lib/Transforms/Scalar/DeadStoreElimination.cpp b/lib/Transforms/Scalar/DeadStoreElimination.cpp
index b9a9b046e83..40986d1a36f 100644
--- a/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -64,8 +64,7 @@ namespace {
     bool runOnBasicBlock(BasicBlock &BB);
     bool HandleFree(CallInst *F);
     bool handleEndBlock(BasicBlock &BB);
-    bool RemoveAccessedObjects(Value *Ptr, uint64_t killPointerSize,
-                               BasicBlock::iterator &BBI,
+    void RemoveAccessedObjects(Value *Ptr, uint64_t killPointerSize,
                                SmallPtrSet<Value*, 16> &deadPointers);
     void DeleteDeadInstruction(Instruction *I,
                                SmallPtrSet<Value*, 16> *deadPointers = 0);
@@ -514,8 +513,7 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
 
     // Remove any allocas from the DeadPointer set that are loaded, as this
     // makes any stores above the access live.
-    MadeChange |= RemoveAccessedObjects(KillPointer, KillPointerSize, BBI,
-                                        DeadStackObjects);
+    RemoveAccessedObjects(KillPointer, KillPointerSize, DeadStackObjects);
 
     // If all of the allocas were clobbered by the access then we're not going
     // to find anything else to process.
@@ -529,53 +527,34 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
 /// RemoveAccessedObjects - Check to see if the specified location may alias any
 /// of the stack objects in the DeadStackObjects set.  If so, they become live
 /// because the location is being loaded.
-bool DSE::RemoveAccessedObjects(Value *KillPointer, uint64_t KillPointerSize,
-                                BasicBlock::iterator &BBI,
+void DSE::RemoveAccessedObjects(Value *KillPointer, uint64_t KillPointerSize,
                                 SmallPtrSet<Value*, 16> &DeadStackObjects) {
   Value *UnderlyingPointer = KillPointer->getUnderlyingObject();
 
   // A constant can't be in the dead pointer set.
   if (isa<Constant>(UnderlyingPointer))
-    return false;
+    return;
   
   // If the kill pointer can be easily reduced to an alloca, don't bother doing
   // extraneous AA queries.
-  if (DeadStackObjects.count(UnderlyingPointer)) {
+  if (isa<AllocaInst>(UnderlyingPointer) || isa<Argument>(UnderlyingPointer)) {
     DeadStackObjects.erase(UnderlyingPointer);
-    return false;
+    return;
   }
   
-  bool MadeChange = false;
   SmallVector<Value*, 16> NowLive;
-  
   for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
        E = DeadStackObjects.end(); I != E; ++I) {
     // See if this pointer could alias it
     AliasAnalysis::AliasResult A = AA->alias(*I, getPointerSize(*I, *AA),
                                              KillPointer, KillPointerSize);
-
-    // If it must-alias and a store, we can delete it
-    if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
-      StoreInst *S = cast<StoreInst>(BBI);
-
-      // Remove it!
-      ++BBI;
-      DeleteDeadInstruction(S, &DeadStackObjects);
-      ++NumFastStores;
-      MadeChange = true;
-
-      continue;
-
-      // Otherwise, it is undead
-    } else if (A != AliasAnalysis::NoAlias)
+    if (A != AliasAnalysis::NoAlias)
       NowLive.push_back(*I);
   }
 
   for (SmallVector<Value*, 16>::iterator I = NowLive.begin(), E = NowLive.end();
        I != E; ++I)
     DeadStackObjects.erase(*I);
-  
-  return MadeChange;
 }
 
 /// DeleteDeadInstruction - Delete this instruction.  Before we do, go through