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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123222 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 23 insertions, 7 deletions

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 2e8c335b37..6de8b85070 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -35,7 +35,7 @@ void 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 FoldSingleEntryPHINodes(BasicBlock *BB);
+void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = 0);
 
 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
 /// is dead. Also recursively delete any operands that become dead as
@@ -46,7 +46,7 @@ bool DeleteDeadPHIs(BasicBlock *BB);
 
 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
 /// if possible.  The return value indicates success or failure.
-bool MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P = 0);
+bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = 0);
 
 // ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
 // with a value, then remove and delete the original instruction.
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index b7fc9c30e0..a4bd7c1eb4 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1741,8 +1741,8 @@ bool GVN::runOnFunction(Function& F) {
   // Merge unconditional branches, allowing PRE to catch more
   // optimization opportunities.
   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
-    BasicBlock *BB = FI;
-    ++FI;
+    BasicBlock *BB = FI++;
+    
     bool removedBlock = MergeBlockIntoPredecessor(BB, this);
     if (removedBlock) ++NumGVNBlocks;
 
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 3daa45cec3..40d33d15af 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/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();