[GVN] Preserve loop related analysis/canonical forms.

LoopInfo can be easily preserved by passing it to the functions that
modify the CFG (SplitCriticalEdge and MergeBlockIntoPredecessor.
SplitCriticalEdge also preserves LoopSimplify and LCSSA form when when passing in
LoopInfo. The test case shows that we preserve LoopSimplify and
LoopInfo. Adding addPreservedID(LCSSAID) did not preserve LCSSA for some
reason.

Also I am not sure if it is possible to preserve those in the new pass
manager, as they aren't analysis passes.

Reviewers: reames, hfinkel, davide, jdoerfert

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D65137

llvm-svn: 367332

2 files changed, 29 insertions, 7 deletions

diff --git a/llvm/lib/Analysis/CFG.cpp b/llvm/lib/Analysis/CFG.cpp
index 18b83d6838c..8215b4ecbb0 100644
--- a/llvm/lib/Analysis/CFG.cpp
+++ b/llvm/lib/Analysis/CFG.cpp
@@ -87,11 +87,18 @@ unsigned llvm::GetSuccessorNumber(const BasicBlock *BB,
 /// with multiple predecessors.
 bool llvm::isCriticalEdge(const Instruction *TI, unsigned SuccNum,
                           bool AllowIdenticalEdges) {
-  assert(TI->isTerminator() && "Must be a terminator to have successors!");
   assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
+  return isCriticalEdge(TI, TI->getSuccessor(SuccNum), AllowIdenticalEdges);
+}
+
+bool llvm::isCriticalEdge(const Instruction *TI, const BasicBlock *Dest,
+                          bool AllowIdenticalEdges) {
+  assert(TI->isTerminator() && "Must be a terminator to have successors!");
   if (TI->getNumSuccessors() == 1) return false;
 
-  const BasicBlock *Dest = TI->getSuccessor(SuccNum);
+  assert(find(predecessors(Dest), TI->getParent()) != pred_end(Dest) &&
+         "No edge between TI's block and Dest.");
+
   const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
 
   // If there is more than one predecessor, this is a critical edge...
diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 1a02e9d33f4..29911a4ed28 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -70,6 +70,7 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
@@ -626,6 +627,8 @@ PreservedAnalyses GVN::run(Function &F, FunctionAnalysisManager &AM) {
   PA.preserve<DominatorTreeAnalysis>();
   PA.preserve<GlobalsAA>();
   PA.preserve<TargetLibraryAnalysis>();
+  if (LI)
+    PA.preserve<LoopAnalysis>();
   return PA;
 }
 
@@ -1976,6 +1979,7 @@ bool GVN::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
   MD = RunMD;
   ImplicitControlFlowTracking ImplicitCFT(DT);
   ICF = &ImplicitCFT;
+  this->LI = LI;
   VN.setMemDep(MD);
   ORE = RunORE;
   InvalidBlockRPONumbers = true;
@@ -2335,7 +2339,7 @@ bool GVN::performPRE(Function &F) {
 /// the block inserted to the critical edge.
 BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) {
   BasicBlock *BB =
-      SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT));
+      SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT, LI));
   if (MD)
     MD->invalidateCachedPredecessors();
   InvalidBlockRPONumbers = true;
@@ -2350,7 +2354,7 @@ bool GVN::splitCriticalEdges() {
   do {
     std::pair<Instruction *, unsigned> Edge = toSplit.pop_back_val();
     SplitCriticalEdge(Edge.first, Edge.second,
-                      CriticalEdgeSplittingOptions(DT));
+                      CriticalEdgeSplittingOptions(DT, LI));
   } while (!toSplit.empty());
   if (MD) MD->invalidateCachedPredecessors();
   InvalidBlockRPONumbers = true;
@@ -2456,18 +2460,26 @@ void GVN::addDeadBlock(BasicBlock *BB) {
     if (DeadBlocks.count(B))
       continue;
 
+    // First, split the critical edges. This might also create additional blocks
+    // to preserve LoopSimplify form and adjust edges accordingly.
     SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B));
     for (BasicBlock *P : Preds) {
       if (!DeadBlocks.count(P))
         continue;
 
-      if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) {
+      if (llvm::any_of(successors(P),
+                       [B](BasicBlock *Succ) { return Succ == B; }) &&
+          isCriticalEdge(P->getTerminator(), B)) {
         if (BasicBlock *S = splitCriticalEdges(P, B))
           DeadBlocks.insert(P = S);
       }
+    }
 
-      for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) {
-        PHINode &Phi = cast<PHINode>(*II);
+    // Now undef the incoming values from the dead predecessors.
+    for (BasicBlock *P : predecessors(B)) {
+      if (!DeadBlocks.count(P))
+        continue;
+      for (PHINode &Phi : B->phis()) {
         Phi.setIncomingValueForBlock(P, UndefValue::get(Phi.getType()));
         if (MD)
           MD->invalidateCachedPointerInfo(&Phi);
@@ -2556,6 +2568,7 @@ public:
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
     if (!NoMemDepAnalysis)
       AU.addRequired<MemoryDependenceWrapperPass>();
     AU.addRequired<AAResultsWrapperPass>();
@@ -2563,6 +2576,8 @@ public:
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<GlobalsAAWrapperPass>();
     AU.addPreserved<TargetLibraryInfoWrapperPass>();
+    AU.addPreserved<LoopInfoWrapperPass>();
+    AU.addPreservedID(LoopSimplifyID);
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
   }