[llvm] r341709 - [MemorySSA] Update MemoryPhi wiring for block splitting to consider if identical edges were merged.

[Alina Sbirlea via llvm-commits]

Author: asbirlea
Date: Fri Sep  7 14:14:48 2018
New Revision: 341709

URL: http://llvm.org/viewvc/llvm-project?rev=341709&view=rev
Log:
[MemorySSA] Update MemoryPhi wiring for block splitting to consider if identical edges were merged.

Summary:
Block splitting is done with either identical edges being merged, or not.
Only critical edges can be split without merging identical edges based on an option.
Teach the memoryssa updater to take this into account: for the same edge between two blocks only move one entry from the Phi in Old to the new Phi in New.

Reviewers: george.burgess.iv

Subscribers: sanjoy, jlebar, Prazek, llvm-commits

Differential Revision: https://reviews.llvm.org/D51563

Modified:
    llvm/trunk/include/llvm/Analysis/MemorySSAUpdater.h
    llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp
    llvm/trunk/lib/Transforms/Utils/BreakCriticalEdges.cpp

Modified: llvm/trunk/include/llvm/Analysis/MemorySSAUpdater.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemorySSAUpdater.h?rev=341709&r1=341708&r2=341709&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/MemorySSAUpdater.h (original)
+++ llvm/trunk/include/llvm/Analysis/MemorySSAUpdater.h Fri Sep  7 14:14:48 2018
@@ -129,10 +129,9 @@ public:
   /// If New is the only predecessor, move Old's Phi, if present, to New.
   /// Otherwise, add a new Phi in New with appropriate incoming values, and
   /// update the incoming values in Old's Phi node too, if present.
-  void
-  wireOldPredecessorsToNewImmediatePredecessor(BasicBlock *Old, BasicBlock *New,
-                                               ArrayRef<BasicBlock *> Preds);
-
+  void wireOldPredecessorsToNewImmediatePredecessor(
+      BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds,
+      bool IdenticalEdgesWereMerged = true);
   // The below are utility functions. Other than creation of accesses to pass
   // to insertDef, and removeAccess to remove accesses, you should generally
   // not attempt to update memoryssa yourself. It is very non-trivial to get

Modified: llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp?rev=341709&r1=341708&r2=341709&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp (original)
+++ llvm/trunk/lib/Analysis/MemorySSAUpdater.cpp Fri Sep  7 14:14:48 2018
@@ -498,7 +498,8 @@ static MemoryAccess *onlySingleValue(Mem
 }
 
 void MemorySSAUpdater::wireOldPredecessorsToNewImmediatePredecessor(
-    BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds) {
+    BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds,
+    bool IdenticalEdgesWereMerged) {
   assert(!MSSA->getWritableBlockAccesses(New) &&
          "Access list should be null for a new block.");
   MemoryPhi *Phi = MSSA->getMemoryAccess(Old);
@@ -513,9 +514,17 @@ void MemorySSAUpdater::wireOldPredecesso
                              "new immediate predecessor.");
     MemoryPhi *NewPhi = MSSA->createMemoryPhi(New);
     SmallPtrSet<BasicBlock *, 16> PredsSet(Preds.begin(), Preds.end());
+    // Currently only support the case of removing a single incoming edge when
+    // identical edges were not merged.
+    if (!IdenticalEdgesWereMerged)
+      assert(PredsSet.size() == Preds.size() &&
+             "If identical edges were not merged, we cannot have duplicate "
+             "blocks in the predecessors");
     Phi->unorderedDeleteIncomingIf([&](MemoryAccess *MA, BasicBlock *B) {
       if (PredsSet.count(B)) {
         NewPhi->addIncoming(MA, B);
+        if (!IdenticalEdgesWereMerged)
+          PredsSet.erase(B);
         return true;
       }
       return false;

Modified: llvm/trunk/lib/Transforms/Utils/BreakCriticalEdges.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/BreakCriticalEdges.cpp?rev=341709&r1=341708&r2=341709&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/BreakCriticalEdges.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/BreakCriticalEdges.cpp Fri Sep  7 14:14:48 2018
@@ -201,7 +201,8 @@ llvm::SplitCriticalEdge(TerminatorInst *
   auto *LI = Options.LI;
   auto *MSSAU = Options.MSSAU;
   if (MSSAU)
-    MSSAU->wireOldPredecessorsToNewImmediatePredecessor(DestBB, NewBB, {TIBB});
+    MSSAU->wireOldPredecessorsToNewImmediatePredecessor(
+        DestBB, NewBB, {TIBB}, Options.MergeIdenticalEdges);
 
   if (!DT && !LI)
     return NewBB;