Update MemorySSA in LoopRotate.

Summary:
Teach LoopRotate to preserve MemorySSA.
Enable tests for correctness, dependency disabled by default.

Subscribers: sanjoy, jlebar, Prazek, george.burgess.iv, llvm-commits

Differential Revision: https://reviews.llvm.org/D51718

llvm-svn: 345216

2 files changed, 75 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index eeaad39dc1d..fd22128f7fe 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -15,6 +15,8 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Support/Debug.h"
@@ -40,12 +42,19 @@ PreservedAnalyses LoopRotatePass::run(Loop &L, LoopAnalysisManager &AM,
   const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
   const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
 
-  bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE, SQ,
-                              false, Threshold, false);
+  Optional<MemorySSAUpdater> MSSAU;
+  if (AR.MSSA)
+    MSSAU = MemorySSAUpdater(AR.MSSA);
+  bool Changed = LoopRotation(&L, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
+                              MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
+                              SQ, false, Threshold, false);
 
   if (!Changed)
     return PreservedAnalyses::all();
 
+  if (AR.MSSA && VerifyMemorySSA)
+    AR.MSSA->verifyMemorySSA();
+
   return getLoopPassPreservedAnalyses();
 }
 
@@ -68,6 +77,10 @@ public:
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
+    if (EnableMSSALoopDependency) {
+      AU.addRequired<MemorySSAWrapperPass>();
+      AU.addPreserved<MemorySSAWrapperPass>();
+    }
     getLoopAnalysisUsage(AU);
   }
 
@@ -84,8 +97,14 @@ public:
     auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
     auto *SE = SEWP ? &SEWP->getSE() : nullptr;
     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
-    return LoopRotation(L, LI, TTI, AC, DT, SE, SQ, false, MaxHeaderSize,
-                        false);
+    Optional<MemorySSAUpdater> MSSAU;
+    if (EnableMSSALoopDependency) {
+      MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
+      MSSAU = MemorySSAUpdater(MSSA);
+    }
+    return LoopRotation(L, LI, TTI, AC, DT, SE,
+                        MSSAU.hasValue() ? MSSAU.getPointer() : nullptr, SQ,
+                        false, MaxHeaderSize, false);
   }
 };
 }
@@ -96,6 +115,7 @@ INITIALIZE_PASS_BEGIN(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops",
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 INITIALIZE_PASS_END(LoopRotateLegacyPass, "loop-rotate", "Rotate Loops", false,
                     false)
 
diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index 73f67f3219d..41f14a83461 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -20,6 +20,8 @@
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -54,6 +56,7 @@ class LoopRotate {
   AssumptionCache *AC;
   DominatorTree *DT;
   ScalarEvolution *SE;
+  MemorySSAUpdater *MSSAU;
   const SimplifyQuery &SQ;
   bool RotationOnly;
   bool IsUtilMode;
@@ -61,10 +64,11 @@ class LoopRotate {
 public:
   LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
              const TargetTransformInfo *TTI, AssumptionCache *AC,
-             DominatorTree *DT, ScalarEvolution *SE, const SimplifyQuery &SQ,
-             bool RotationOnly, bool IsUtilMode)
+             DominatorTree *DT, ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
+             const SimplifyQuery &SQ, bool RotationOnly, bool IsUtilMode)
       : MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
-        SQ(SQ), RotationOnly(RotationOnly), IsUtilMode(IsUtilMode) {}
+        MSSAU(MSSAU), SQ(SQ), RotationOnly(RotationOnly),
+        IsUtilMode(IsUtilMode) {}
   bool processLoop(Loop *L);
 
 private:
@@ -269,6 +273,8 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     SE->forgetTopmostLoop(L);
 
   LLVM_DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
 
   // Find new Loop header. NewHeader is a Header's one and only successor
   // that is inside loop.  Header's other successor is outside the
@@ -385,6 +391,12 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
   // remove the corresponding incoming values from the PHI nodes in OrigHeader.
   LoopEntryBranch->eraseFromParent();
 
+  // Update MemorySSA before the rewrite call below changes the 1:1
+  // instruction:cloned_instruction_or_value mapping in ValueMap.
+  if (MSSAU) {
+    ValueMap[OrigHeader] = OrigPreheader;
+    MSSAU->updateForClonedBlockIntoPred(OrigHeader, OrigPreheader, ValueMap);
+  }
 
   SmallVector<PHINode*, 2> InsertedPHIs;
   // If there were any uses of instructions in the duplicated block outside the
@@ -411,6 +423,12 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
     Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
     DT->applyUpdates(Updates);
+
+    if (MSSAU) {
+      MSSAU->applyUpdates(Updates, *DT);
+      if (VerifyMemorySSA)
+        MSSAU->getMemorySSA()->verifyMemorySSA();
+    }
   }
 
   // At this point, we've finished our major CFG changes.  As part of cloning
@@ -433,7 +451,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     // Split the edge to form a real preheader.
     BasicBlock *NewPH = SplitCriticalEdge(
         OrigPreheader, NewHeader,
-        CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
+        CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
     NewPH->setName(NewHeader->getName() + ".lr.ph");
 
     // Preserve canonical loop form, which means that 'Exit' should have only
@@ -452,7 +470,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
       SplitLatchEdge |= L->getLoopLatch() == ExitPred;
       BasicBlock *ExitSplit = SplitCriticalEdge(
           ExitPred, Exit,
-          CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
+          CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
       ExitSplit->moveBefore(Exit);
     }
     assert(SplitLatchEdge &&
@@ -467,17 +485,27 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
 
     // With our CFG finalized, update DomTree if it is available.
     if (DT) DT->deleteEdge(OrigPreheader, Exit);
+
+    // Update MSSA too, if available.
+    if (MSSAU)
+      MSSAU->removeEdge(OrigPreheader, Exit);
   }
 
   assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
   assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
 
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
+
   // Now that the CFG and DomTree are in a consistent state again, try to merge
   // the OrigHeader block into OrigLatch.  This will succeed if they are
   // connected by an unconditional branch.  This is just a cleanup so the
   // emitted code isn't too gross in this common case.
   DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
-  MergeBlockIntoPredecessor(OrigHeader, &DTU, LI);
+  MergeBlockIntoPredecessor(OrigHeader, &DTU, LI, MSSAU);
+
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
 
   LLVM_DEBUG(dbgs() << "LoopRotation: into "; L->dump());
 
@@ -586,9 +614,14 @@ bool LoopRotate::simplifyLoopLatch(Loop *L) {
                     << LastExit->getName() << "\n");
 
   // Hoist the instructions from Latch into LastExit.
+  Instruction *FirstLatchInst = &*(Latch->begin());
   LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
                                  Latch->begin(), Jmp->getIterator());
 
+  // Update MemorySSA
+  if (MSSAU)
+    MSSAU->moveAllAfterMergeBlocks(Latch, LastExit, FirstLatchInst);
+
   unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
   BasicBlock *Header = Jmp->getSuccessor(0);
   assert(Header == L->getHeader() && "expected a backward branch");
@@ -604,6 +637,10 @@ bool LoopRotate::simplifyLoopLatch(Loop *L) {
   if (DT)
     DT->eraseNode(Latch);
   Latch->eraseFromParent();
+
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
+
   return true;
 }
 
@@ -636,11 +673,16 @@ bool LoopRotate::processLoop(Loop *L) {
 /// The utility to convert a loop into a loop with bottom test.
 bool llvm::LoopRotation(Loop *L, LoopInfo *LI, const TargetTransformInfo *TTI,
                         AssumptionCache *AC, DominatorTree *DT,
-                        ScalarEvolution *SE, const SimplifyQuery &SQ,
-                        bool RotationOnly = true,
+                        ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
+                        const SimplifyQuery &SQ, bool RotationOnly = true,
                         unsigned Threshold = unsigned(-1),
                         bool IsUtilMode = true) {
-  LoopRotate LR(Threshold, LI, TTI, AC, DT, SE, SQ, RotationOnly, IsUtilMode);
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
+  LoopRotate LR(Threshold, LI, TTI, AC, DT, SE, MSSAU, SQ, RotationOnly,
+                IsUtilMode);
+  if (MSSAU && VerifyMemorySSA)
+    MSSAU->getMemorySSA()->verifyMemorySSA();
 
   return LR.processLoop(L);
 }