[LoopSimplifyCFG] Update MemorySSA after r353911.

Summary:
MemorySSA is not properly updated in LoopSimplifyCFG after recent changes. Use SplitBlock utility to resolve that and clear all updates once handleDeadExits is finished.
All updates that follow are removal of edges which are safe to handle via the removeEdge() API.
Also, deleting dead blocks is done correctly as is, i.e. delete from MemorySSA before updating the CFG and DT.

Reviewers: mkazantsev, rtereshin

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58524

llvm-svn: 354613

1 files changed, 17 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
index bbf35513416..b565cb9c236 100644
--- a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -352,14 +352,9 @@ private:
     // Construct split preheader and the dummy switch to thread edges from it to
     // dead exits.
     BasicBlock *Preheader = L.getLoopPreheader();
-    BasicBlock *NewPreheader = Preheader->splitBasicBlock(
-        Preheader->getTerminator(),
-        Twine(Preheader->getName()).concat("-split"));
-    if (MSSAU)
-      MSSAU->removeEdge(Preheader, L.getHeader());
-    DTUpdates.push_back({DominatorTree::Delete, Preheader, L.getHeader()});
-    DTUpdates.push_back({DominatorTree::Insert, NewPreheader, L.getHeader()});
-    DTUpdates.push_back({DominatorTree::Insert, Preheader, NewPreheader});
+    BasicBlock *NewPreheader = llvm::SplitBlock(
+        Preheader, Preheader->getTerminator(), &DT, &LI, MSSAU);
+
     IRBuilder<> Builder(Preheader->getTerminator());
     SwitchInst *DummySwitch =
         Builder.CreateSwitch(Builder.getInt32(0), NewPreheader);
@@ -384,8 +379,6 @@ private:
 
     assert(L.getLoopPreheader() == NewPreheader && "Malformed CFG?");
     if (Loop *OuterLoop = LI.getLoopFor(Preheader)) {
-      OuterLoop->addBasicBlockToLoop(NewPreheader, LI);
-
       // When we break dead edges, the outer loop may become unreachable from
       // the current loop. We need to fix loop info accordingly. For this, we
       // find the most nested loop that still contains L and remove L from all
@@ -414,10 +407,21 @@ private:
         assert(FixLCSSALoop && "Should be a loop!");
         // We need all DT updates to be done before forming LCSSA.
         DTU.applyUpdates(DTUpdates);
+        if (MSSAU)
+          MSSAU->applyUpdates(DTUpdates, DT);
         DTUpdates.clear();
         formLCSSARecursively(*FixLCSSALoop, DT, &LI, &SE);
       }
     }
+
+    if (MSSAU) {
+      // Clear all updates now. Facilitates deletes that follow.
+      DTU.applyUpdates(DTUpdates);
+      MSSAU->applyUpdates(DTUpdates, DT);
+      DTUpdates.clear();
+      if (VerifyMemorySSA)
+        MSSAU->getMemorySSA()->verifyMemorySSA();
+    }
   }
 
   /// Delete loop blocks that have become unreachable after folding. Make all
@@ -589,6 +593,9 @@ public:
       DTUpdates.clear();
     }
 
+    if (MSSAU && VerifyMemorySSA)
+      MSSAU->getMemorySSA()->verifyMemorySSA();
+
 #ifndef NDEBUG
     // Make sure that we have preserved all data structures after the transform.
     assert(DT.verify() && "DT broken after transform!");