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

diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 2e8c335b372a5e5974d442a25502aef8074d5939..6de8b850704b09df26a5d0c9cc406fe011cf8d6b 100644 (file)
--- 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 b7fc9c30e06d6a3b3e1f542a0023046bff432535..a4bd7c1eb4234d4a7d93ac5f2bb011b520b914ce 100644 (file)
--- 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 3daa45cec360a47ef35f0218979b817bad28b918..40d33d15afc2fb394b7d4a901d191d2e9be4fe61 100644 (file)
--- 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();