Re-apply r80926, with fixes: keep the domtree informed of new blocks

that get created during loop unswitching, and fix SplitBlockPredecessors'
LCSSA updating code to create new PHIs instead of trying to just move
existing ones.

Also, optimize Loop::verifyLoop, since it gets called a lot. Use
searches on a sorted list of blocks instead of calling the "contains"
function, as is done in other places in the Loop class, since "contains"
does a linear search. Also, don't call verifyLoop from LoopSimplify or
LCSSA, as the PassManager is already calling verifyLoop as part of
LoopInfo's verifyAnalysis.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81221 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 161 insertions, 63 deletions

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index c165e04fb8..736d26e75f 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Scalar.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ValueHandle.h"
 #include <algorithm>
@@ -319,7 +320,8 @@ BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
     ++SplitIt;
   BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
 
-  // The new block lives in whichever loop the old one did.
+  // The new block lives in whichever loop the old one did. This preserves
+  // LCSSA as well, because we force the split point to be after any PHI nodes.
   if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>())
     if (Loop *L = LI->getLoopFor(Old))
       L->addBasicBlockToLoop(New, LI->getBase());
@@ -353,8 +355,12 @@ BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
 /// Preds array, which has NumPreds elements in it.  The new block is given a
 /// suffix of 'Suffix'.
 ///
-/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and
-/// DominanceFrontier, but no other analyses.
+/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
+/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
+/// In particular, it does not preserve LoopSimplify (because it's
+/// complicated to handle the case where one of the edges being split
+/// is an exit of a loop with other exits).
+///
 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 
                                          BasicBlock *const *Preds,
                                          unsigned NumPreds, const char *Suffix,
@@ -366,19 +372,44 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
   // The new block unconditionally branches to the old block.
   BranchInst *BI = BranchInst::Create(BB, NewBB);
   
+  LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0;
+  Loop *L = LI ? LI->getLoopFor(BB) : 0;
+  bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
+
   // Move the edges from Preds to point to NewBB instead of BB.
-  for (unsigned i = 0; i != NumPreds; ++i)
+  // While here, if we need to preserve loop analyses, collect
+  // some information about how this split will affect loops.
+  bool HasLoopExit = false;
+  bool IsLoopEntry = !!L;
+  bool SplitMakesNewLoopHeader = false;
+  for (unsigned i = 0; i != NumPreds; ++i) {
     Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
-  
+
+    if (LI) {
+      // If we need to preserve LCSSA, determine if any of
+      // the preds is a loop exit.
+      if (PreserveLCSSA)
+        if (Loop *PL = LI->getLoopFor(Preds[i]))
+          if (!PL->contains(BB))
+            HasLoopExit = true;
+      // If we need to preserve LoopInfo, note whether any of the
+      // preds crosses an interesting loop boundary.
+      if (L) {
+        if (L->contains(Preds[i]))
+          IsLoopEntry = false;
+        else
+          SplitMakesNewLoopHeader = true;
+      }
+    }
+  }
+
   // Update dominator tree and dominator frontier if available.
   DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0;
   if (DT)
     DT->splitBlock(NewBB);
   if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0)
     DF->splitBlock(NewBB);
-  AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
-  
-  
+
   // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
   // node becomes an incoming value for BB's phi node.  However, if the Preds
   // list is empty, we need to insert dummy entries into the PHI nodes in BB to
@@ -389,20 +420,42 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
       cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
     return NewBB;
   }
+
+  AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
+
+  if (L) {
+    if (IsLoopEntry) {
+      if (Loop *PredLoop = LI->getLoopFor(Preds[0])) {
+        // Add the new block to the nearest enclosing loop (and not an
+        // adjacent loop).
+        while (PredLoop && !PredLoop->contains(BB))
+          PredLoop = PredLoop->getParentLoop();
+        if (PredLoop)
+          PredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
+      }
+    } else {
+      L->addBasicBlockToLoop(NewBB, LI->getBase());
+      if (SplitMakesNewLoopHeader)
+        L->moveToHeader(NewBB);
+    }
+  }
   
   // Otherwise, create a new PHI node in NewBB for each PHI node in BB.
   for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
     PHINode *PN = cast<PHINode>(I++);
     
     // Check to see if all of the values coming in are the same.  If so, we
-    // don't need to create a new PHI node.
-    Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
-    for (unsigned i = 1; i != NumPreds; ++i)
-      if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
-        InVal = 0;
-        break;
-      }
-    
+    // don't need to create a new PHI node, unless it's needed for LCSSA.
+    Value *InVal = 0;
+    if (!HasLoopExit) {
+      InVal = PN->getIncomingValueForBlock(Preds[0]);
+      for (unsigned i = 1; i != NumPreds; ++i)
+        if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
+          InVal = 0;
+          break;
+        }
+    }
+
     if (InVal) {
       // If all incoming values for the new PHI would be the same, just don't
       // make a new PHI.  Instead, just remove the incoming values from the old
@@ -427,13 +480,6 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
     // Add an incoming value to the PHI node in the loop for the preheader
     // edge.
     PN->addIncoming(InVal, NewBB);
-    
-    // Check to see if we can eliminate this phi node.
-    if (Value *V = PN->hasConstantValue(DT)) {
-      PN->replaceAllUsesWith(V);
-      if (AA) AA->deleteValue(PN);
-      PN->eraseFromParent();
-    }
   }
   
   return NewBB;
diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp
index 632aa2b723..59350a71a7 100644
--- a/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -122,9 +122,9 @@ bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
 /// false otherwise.  This ensures that all edges to that dest go to one block
 /// instead of each going to a different block.
 //
-bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P,
-                             bool MergeIdenticalEdges) {
-  if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return false;
+BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
+                                    Pass *P, bool MergeIdenticalEdges) {
+  if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;
   BasicBlock *TIBB = TI->getParent();
   BasicBlock *DestBB = TI->getSuccessor(SuccNum);
 
@@ -172,7 +172,7 @@ bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P,
   
 
   // If we don't have a pass object, we can't update anything...
-  if (P == 0) return true;
+  if (P == 0) return NewBB;
 
   // Now update analysis information.  Since the only predecessor of NewBB is
   // the TIBB, TIBB clearly dominates NewBB.  TIBB usually doesn't dominate
@@ -254,9 +254,9 @@ bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P,
   
   // Update LoopInfo if it is around.
   if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>()) {
-    // If one or the other blocks were not in a loop, the new block is not
-    // either, and thus LI doesn't need to be updated.
-    if (Loop *TIL = LI->getLoopFor(TIBB))
+    if (Loop *TIL = LI->getLoopFor(TIBB)) {
+      // If one or the other blocks were not in a loop, the new block is not
+      // either, and thus LI doesn't need to be updated.
       if (Loop *DestLoop = LI->getLoopFor(DestBB)) {
         if (TIL == DestLoop) {
           // Both in the same loop, the NewBB joins loop.
@@ -278,6 +278,65 @@ bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P,
             P->addBasicBlockToLoop(NewBB, LI->getBase());
         }
       }
+      // If TIBB is in a loop and DestBB is outside of that loop, split the
+      // other exit blocks of the loop that also have predecessors outside
+      // the loop, to maintain a LoopSimplify guarantee.
+      if (!TIL->contains(DestBB) &&
+          P->mustPreserveAnalysisID(LoopSimplifyID)) {
+        // For each unique exit block...
+        SmallVector<BasicBlock *, 4> ExitBlocks;
+        TIL->getExitBlocks(ExitBlocks);
+        for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+          // Collect all the preds that are inside the loop, and note
+          // whether there are any preds outside the loop.
+          SmallVector<BasicBlock *, 4> Preds;
+          bool AllPredsInLoop = false;
+          BasicBlock *Exit = ExitBlocks[i];
+          for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit);
+               I != E; ++I)
+            if (TIL->contains(*I))
+              Preds.push_back(*I);
+            else
+              AllPredsInLoop = true;
+          // If there are any preds not in the loop, we'll need to split
+          // the edges. The Preds.empty() check is needed because a block
+          // may appear multiple times in the list. We can't use
+          // getUniqueExitBlocks above because that depends on LoopSimplify
+          // form, which we're in the process of restoring!
+          if (Preds.empty() || !AllPredsInLoop) continue;
+          BasicBlock *NewBB = SplitBlockPredecessors(Exit,
+                                                     Preds.data(), Preds.size(),
+                                                     "split", P);
+          // Update LCSSA form by creating new PHIs in the new exit blocks
+          // as needed.
+          if (P->mustPreserveAnalysisID(LCSSAID))
+            for (BasicBlock::iterator I = Exit->begin();
+                 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+              unsigned Idx = PN->getBasicBlockIndex(NewBB);
+              Value *V = PN->getIncomingValue(Idx);
+              // If the PHI is already suitable, don't create a new one.
+              if (PHINode *VP = dyn_cast<PHINode>(V))
+                if (VP->getParent() == NewBB)
+                  continue;
+              // A new PHI is needed. Create one and populate it.
+              PHINode *NewPN =
+                PHINode::Create(PN->getType(), "split", NewBB->getTerminator());
+              for (unsigned i = 0, e = Preds.size(); i != e; ++i)
+                NewPN->addIncoming(V, Preds[i]);
+              PN->setIncomingValue(Idx, NewPN);
+            }
+        }
+      }
+      // LCSSA form was updated above for the case where LoopSimplify is
+      // available, which means that all predecessors of loop exit blocks
+      // are within the loop. Without LoopSimplify form, it would be
+      // necessary to insert a new phi.
+      assert((!P->mustPreserveAnalysisID(LCSSAID) ||
+              P->mustPreserveAnalysisID(LoopSimplifyID)) &&
+             "SplitCriticalEdge doesn't know how to update LCCSA form "
+             "without LoopSimplify!");
+    }
   }
-  return true;
+
+  return NewBB;
 }
diff --git a/lib/Transforms/Utils/LCSSA.cpp b/lib/Transforms/Utils/LCSSA.cpp
index 84fcc643bf..b510262c05 100644
--- a/lib/Transforms/Utils/LCSSA.cpp
+++ b/lib/Transforms/Utils/LCSSA.cpp
@@ -58,6 +58,7 @@ namespace {
     DominatorTree *DT;
     std::vector<BasicBlock*> LoopBlocks;
     PredIteratorCache PredCache;
+    Loop *L;
     
     virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
 
@@ -72,9 +73,9 @@ namespace {
       AU.setPreservesCFG();
       AU.addRequiredID(LoopSimplifyID);
       AU.addPreservedID(LoopSimplifyID);
-      AU.addRequired<LoopInfo>();
+      AU.addRequiredTransitive<LoopInfo>();
       AU.addPreserved<LoopInfo>();
-      AU.addRequired<DominatorTree>();
+      AU.addRequiredTransitive<DominatorTree>();
       AU.addPreserved<ScalarEvolution>();
       AU.addPreserved<DominatorTree>();
 
@@ -86,6 +87,15 @@ namespace {
       AU.addPreserved<DominanceFrontier>();
     }
   private:
+
+    /// verifyAnalysis() - Verify loop nest.
+    virtual void verifyAnalysis() const {
+#ifndef NDEBUG
+      // Check the special guarantees that LCSSA makes.
+      assert(L->isLCSSAForm());
+#endif
+    }
+
     void getLoopValuesUsedOutsideLoop(Loop *L,
                                       SetVector<Instruction*> &AffectedValues,
                                  const SmallVector<BasicBlock*, 8>& exitBlocks);
@@ -107,7 +117,8 @@ Pass *llvm::createLCSSAPass() { return new LCSSA(); }
 const PassInfo *const llvm::LCSSAID = &X;
 
 /// runOnFunction - Process all loops in the function, inner-most out.
-bool LCSSA::runOnLoop(Loop *L, LPPassManager &LPM) {
+bool LCSSA::runOnLoop(Loop *l, LPPassManager &LPM) {
+  L = l;
   PredCache.clear();
   
   LI = &LPM.getAnalysis<LoopInfo>();
diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index 56e5a46cb7..2ff9f8be4b 100644
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -69,8 +69,8 @@ namespace {
 
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       // We need loop information to identify the loops...
-      AU.addRequired<LoopInfo>();
-      AU.addRequired<DominatorTree>();
+      AU.addRequiredTransitive<LoopInfo>();
+      AU.addRequiredTransitive<DominatorTree>();
 
       AU.addPreserved<LoopInfo>();
       AU.addPreserved<DominatorTree>();
@@ -83,9 +83,11 @@ namespace {
     void verifyAnalysis() const {
 #ifndef NDEBUG
       LoopInfo *NLI = &getAnalysis<LoopInfo>();
-      for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I) 
-        (*I)->verifyLoop();
-#endif  
+      for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I) {
+        // Check the special guarantees that LoopSimplify makes.
+        assert((*I)->isLoopSimplifyForm());
+      }
+#endif
     }
 
   private:
@@ -346,15 +348,6 @@ BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
   BasicBlock *NewBB =
     SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
                            ".preheader", this);
-  
-
-  //===--------------------------------------------------------------------===//
-  //  Update analysis results now that we have performed the transformation
-  //
-
-  // We know that we have loop information to update... update it now.
-  if (Loop *Parent = L->getParentLoop())
-    Parent->addBasicBlockToLoop(NewBB, LI->getBase());
 
   // Make sure that NewBB is put someplace intelligent, which doesn't mess up
   // code layout too horribly.
@@ -377,17 +370,6 @@ BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
                                              LoopBlocks.size(), ".loopexit",
                                              this);
 
-  // Update Loop Information - we know that the new block will be in whichever
-  // loop the Exit block is in.  Note that it may not be in that immediate loop,
-  // if the successor is some other loop header.  In that case, we continue 
-  // walking up the loop tree to find a loop that contains both the successor
-  // block and the predecessor block.
-  Loop *SuccLoop = LI->getLoopFor(Exit);
-  while (SuccLoop && !SuccLoop->contains(L->getHeader()))
-    SuccLoop = SuccLoop->getParentLoop();
-  if (SuccLoop)
-    SuccLoop->addBasicBlockToLoop(NewBB, LI->getBase());
-
   return NewBB;
 }
 
@@ -521,10 +503,6 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
   else
     LI->changeTopLevelLoop(L, NewOuter);
 
-  // This block is going to be our new header block: add it to this loop and all
-  // parent loops.
-  NewOuter->addBasicBlockToLoop(NewBB, LI->getBase());
-
   // L is now a subloop of our outer loop.
   NewOuter->addChildLoop(L);
 
@@ -532,6 +510,10 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
        I != E; ++I)
     NewOuter->addBlockEntry(*I);
 
+  // Now reset the header in L, which had been moved by
+  // SplitBlockPredecessors for the outer loop.
+  L->moveToHeader(Header);
+
   // Determine which blocks should stay in L and which should be moved out to
   // the Outer loop now.
   std::set<BasicBlock*> BlocksInL;