Fix FoldSingleEntryPHINodes to update memdep and AA when it deletes

phi nodes.  It is called from MergeBlockIntoPredecessor which is 
called from GVN, which claims to preserve these.

I'm skeptical that this is the actual problem behind PR8954, but
this is a stab in the right direction.

llvm-svn: 123222

1 files changed, 19 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 3daa45cec36..40d33d15afc 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -19,8 +19,9 @@
 #include "llvm/Constant.h"
 #include "llvm/Type.h"
 #include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/DominanceFrontier.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Scalar.h"
@@ -63,12 +64,27 @@ void llvm::DeleteDeadBlock(BasicBlock *BB) {
 /// any single-entry PHI nodes in it, fold them away.  This handles the case
 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
 /// when the block has exactly one predecessor.
-void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
+void llvm::FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P) {
+  if (!isa<PHINode>(BB->begin())) return;
+  
+  AliasAnalysis *AA = 0;
+  MemoryDependenceAnalysis *MemDep = 0;
+  if (P) {
+    AA = P->getAnalysisIfAvailable<AliasAnalysis>();
+    MemDep = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>();
+  }
+  
   while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
     if (PN->getIncomingValue(0) != PN)
       PN->replaceAllUsesWith(PN->getIncomingValue(0));
     else
       PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+    
+    if (MemDep)
+      MemDep->removeInstruction(PN);  // Memdep updates AA itself.
+    else if (AA && isa<PointerType>(PN->getType()))
+      AA->deleteValue(PN);
+    
     PN->eraseFromParent();
   }
 }
@@ -132,7 +148,7 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
 
   // Begin by getting rid of unneeded PHIs.
   if (isa<PHINode>(BB->front()))
-    FoldSingleEntryPHINodes(BB);
+    FoldSingleEntryPHINodes(BB, P);
   
   // Delete the unconditional branch from the predecessor...
   PredBB->getInstList().pop_back();