Revert r275883 and r275891. They seem to cause PR28608.

Revert "[LoopSimplify] Update LCSSA after separating nested loops."

This reverts commit r275891.

Revert "[LCSSA] Post-process PHI-nodes created by SSAUpdate when constructing LCSSA form."

This reverts commit r275883.

llvm-svn: 276064

2 files changed, 13 insertions, 60 deletions

diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
index bee6e24d25a..9658966779b 100644
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -115,8 +115,7 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
     SmallVector<PHINode *, 16> AddedPHIs;
     SmallVector<PHINode *, 8> PostProcessPHIs;
 
-    SmallVector<PHINode *, 4> InsertedPHIs;
-    SSAUpdater SSAUpdate(&InsertedPHIs);
+    SSAUpdater SSAUpdate;
     SSAUpdate.Initialize(I->getType(), I->getName());
 
     // Insert the LCSSA phi's into all of the exit blocks dominated by the
@@ -185,14 +184,6 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
 
       // Otherwise, do full PHI insertion.
       SSAUpdate.RewriteUse(*UseToRewrite);
-
-      // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
-      // to post-process them to keep LCSSA form.
-      for (PHINode *InsertedPN : InsertedPHIs) {
-        if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
-          if (!L->contains(OtherLoop))
-            PostProcessPHIs.push_back(InsertedPN);
-      }
     }
 
     // Post process PHI instructions that were inserted into another disjoint
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 2846e8f235b..b3a928bf775 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -327,8 +327,6 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
     else
       NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
 
-  SmallVector<BasicBlock *, 8> OuterLoopBlocks;
-  OuterLoopBlocks.push_back(NewBB);
   // Now that we know which blocks are in L and which need to be moved to
   // OuterLoop, move any blocks that need it.
   for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
@@ -336,53 +334,12 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
     if (!BlocksInL.count(BB)) {
       // Move this block to the parent, updating the exit blocks sets
       L->removeBlockFromLoop(BB);
-      if ((*LI)[BB] == L) {
+      if ((*LI)[BB] == L)
         LI->changeLoopFor(BB, NewOuter);
-        OuterLoopBlocks.push_back(BB);
-      }
       --i;
     }
   }
 
-  // Split edges to exit blocks from the inner loop, if they emerged in the
-  // process of separating the outer one.
-  SmallVector<BasicBlock *, 8> ExitBlocks;
-  L->getExitBlocks(ExitBlocks);
-  SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
-                                               ExitBlocks.end());
-  for (BasicBlock *ExitBlock : ExitBlockSet) {
-    if (any_of(predecessors(ExitBlock),
-               [L](BasicBlock *BB) { return !L->contains(BB); })) {
-      rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
-    }
-  }
-
-  if (PreserveLCSSA) {
-    // Fix LCSSA form for L. Some values, which previously were only used inside
-    // L, can now be used in NewOuter loop. We need to insert phi-nodes for them
-    // in corresponding exit blocks.
-
-    // Go through all instructions in OuterLoopBlocks and check if they are
-    // using operands from the inner loop. In this case we'll need to fix LCSSA
-    // for these instructions.
-    SmallSetVector<Instruction *, 8> WorklistSet;
-    for (BasicBlock *OuterBB: OuterLoopBlocks) {
-      for (Instruction &I : *OuterBB) {
-        for (Value *Op : I.operands()) {
-          Instruction *OpI = dyn_cast<Instruction>(Op);
-          if (!OpI || !L->contains(OpI))
-            continue;
-          WorklistSet.insert(OpI);
-        }
-      }
-    }
-    SmallVector<Instruction *, 8> Worklist(WorklistSet.begin(),
-                                           WorklistSet.end());
-    formLCSSAForInstructions(Worklist, *DT, *LI);
-    assert(NewOuter->isRecursivelyLCSSAForm(*DT) &&
-           "LCSSA is broken after separating nested loops!");
-  }
-
   return NewOuter;
 }
 
@@ -584,12 +541,17 @@ ReprocessLoop:
   SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
                                                ExitBlocks.end());
   for (BasicBlock *ExitBlock : ExitBlockSet) {
-    if (any_of(predecessors(ExitBlock),
-               [L](BasicBlock *BB) { return !L->contains(BB); })) {
-      rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
-      ++NumInserted;
-      Changed = true;
-    }
+    for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
+         PI != PE; ++PI)
+      // Must be exactly this loop: no subloops, parent loops, or non-loop preds
+      // allowed.
+      if (!L->contains(*PI)) {
+        if (rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA)) {
+          ++NumInserted;
+          Changed = true;
+        }
+        break;
+      }
   }
 
   // If the header has more than two predecessors at this point (from the