From a866c660db9342075ce9362b31650edb244787ad Mon Sep 17 00:00:00 2001
From: Bob Wilson <bob.wilson@apple.com>
Date: Tue, 16 Feb 2010 19:51:59 +0000
Subject: [PATCH] Split critical edges as needed for load PRE.

llvm-svn: 96378
---
 .../llvm/Analysis/MemoryDependenceAnalysis.h  |  7 +++-
 lib/Analysis/MemoryDependenceAnalysis.cpp     |  7 ++++
 lib/Transforms/Scalar/GVN.cpp                 | 38 +++++++++++++++----
 3 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/include/llvm/Analysis/MemoryDependenceAnalysis.h b/include/llvm/Analysis/MemoryDependenceAnalysis.h
index f83cc4f710e..f6aab03690f 100644
--- a/include/llvm/Analysis/MemoryDependenceAnalysis.h
+++ b/include/llvm/Analysis/MemoryDependenceAnalysis.h
@@ -249,7 +249,7 @@ namespace llvm {
                      SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
     ReverseDepMapType ReverseLocalDeps;
     
-    // A reverse mapping form dependencies to the non-local dependees.
+    // A reverse mapping from dependencies to the non-local dependees.
     ReverseDepMapType ReverseNonLocalDeps;
     
     /// Current AA implementation, just a cache.
@@ -312,6 +312,11 @@ namespace llvm {
     /// value and replaces the other value with ptr. This can make Ptr available
     /// in more places that cached info does not necessarily keep.
     void invalidateCachedPointerInfo(Value *Ptr);
+
+    /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
+    /// This needs to be done when the CFG changes, e.g., due to splitting
+    /// critical edges.
+    void invalidateCachedPredecessors();
     
   private:
     MemDepResult getPointerDependencyFrom(Value *Pointer, uint64_t MemSize,
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 183edf4618b..04641e818f8 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -1016,6 +1016,13 @@ void MemoryDependenceAnalysis::invalidateCachedPointerInfo(Value *Ptr) {
   RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(Ptr, true));
 }
 
+/// invalidateCachedPredecessors - Clear the PredIteratorCache info.
+/// This needs to be done when the CFG changes, e.g., due to splitting
+/// critical edges.
+void MemoryDependenceAnalysis::invalidateCachedPredecessors() {
+  PredCache->clear();
+}
+
 /// removeInstruction - Remove an instruction from the dependence analysis,
 /// updating the dependence of instructions that previously depended on it.
 /// This method attempts to keep the cache coherent using the reverse map.
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index b3a8687fc04..c144e16f48e 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -674,6 +674,9 @@ namespace {
     ValueTable VN;
     DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
 
+    // List of critical edges to be split between iterations.
+    SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
+
     // This transformation requires dominator postdominator info
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addRequired<DominatorTree>();
@@ -701,6 +704,7 @@ namespace {
     Value *lookupNumber(BasicBlock *BB, uint32_t num);
     void cleanupGlobalSets();
     void verifyRemoved(const Instruction *I) const;
+    bool splitCriticalEdges();
   };
 
   char GVN::ID = 0;
@@ -1583,10 +1587,15 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
       continue;
     }
     PredLoads[Pred] = 0;
-    // We don't currently handle critical edges :(
+
     if (Pred->getTerminator()->getNumSuccessors() != 1) {
-      DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
-            << Pred->getName() << "': " << *LI << '\n');
+      if (isa<IndirectBrInst>(Pred->getTerminator())) {
+        DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
+              << Pred->getName() << "': " << *LI << '\n');
+        return false;
+      }
+      unsigned SuccNum = SuccessorNumber(Pred, LoadBB);
+      toSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
       return false;
     }
   }
@@ -2004,6 +2013,8 @@ bool GVN::runOnFunction(Function& F) {
   while (ShouldContinue) {
     DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
     ShouldContinue = iterateOnFunction(F);
+    if (splitCriticalEdges())
+      ShouldContinue = true;
     Changed |= ShouldContinue;
     ++Iteration;
   }
@@ -2070,7 +2081,6 @@ bool GVN::processBlock(BasicBlock *BB) {
 /// control flow patterns and attempts to perform simple PRE at the join point.
 bool GVN::performPRE(Function &F) {
   bool Changed = false;
-  SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
   DenseMap<BasicBlock*, Value*> predMap;
   for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
        DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
@@ -2209,11 +2219,23 @@ bool GVN::performPRE(Function &F) {
     }
   }
 
-  for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
-       I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
-    SplitCriticalEdge(I->first, I->second, this);
+  if (splitCriticalEdges())
+    Changed = true;
 
-  return Changed || toSplit.size();
+  return Changed;
+}
+
+/// splitCriticalEdges - Split critical edges found during the previous
+/// iteration that may enable further optimization.
+bool GVN::splitCriticalEdges() {
+  if (toSplit.empty())
+    return false;
+  do {
+    std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
+    SplitCriticalEdge(Edge.first, Edge.second, this);
+  } while (!toSplit.empty());
+  MD->invalidateCachedPredecessors();
+  return true;
 }
 
 /// iterateOnFunction - Executes one iteration of GVN