Make loop preheader insertion in LoopSimplify handle the case where the loop header is a landing pad correctly (by splitting the landingpad out of the loop header). Make some adjustments to the rest of LoopSimplify to make it clear that the rest of LoopSimplify isn't making bad assumptions about the presence of landing pads. PR11575.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146621 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 16 deletions

diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index 904c6fee45..437626552b 100644
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -99,7 +99,8 @@ namespace {
     bool ProcessLoop(Loop *L, LPPassManager &LPM);
     BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
     BasicBlock *InsertPreheaderForLoop(Loop *L);
-    Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
+    Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM,
+                             BasicBlock *Preheader);
     BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
     void PlaceSplitBlockCarefully(BasicBlock *NewBB,
                                   SmallVectorImpl<BasicBlock*> &SplitPreds,
@@ -240,7 +241,7 @@ ReprocessLoop:
     // this for loops with a giant number of backedges, just factor them into a
     // common backedge instead.
     if (L->getNumBackEdges() < 8) {
-      if (SeparateNestedLoop(L, LPM)) {
+      if (SeparateNestedLoop(L, LPM, Preheader)) {
         ++NumNested;
         // This is a big restructuring change, reprocess the whole loop.
         Changed = true;
@@ -379,18 +380,27 @@ BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
   }
 
   // Split out the loop pre-header.
-  BasicBlock *NewBB =
-    SplitBlockPredecessors(Header, OutsideBlocks, ".preheader", this);
+  BasicBlock *PreheaderBB;
+  if (!Header->isLandingPad()) {
+    PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
+                                         this);
+  } else {
+    SmallVector<BasicBlock*, 2> NewBBs;
+    SplitLandingPadPredecessors(Header, OutsideBlocks, ".preheader", 
+                                ".split-lp", this, NewBBs);
+    PreheaderBB = NewBBs[0];
+  }
 
-  NewBB->getTerminator()->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());
-  DEBUG(dbgs() << "LoopSimplify: Creating pre-header " << NewBB->getName()
-               << "\n");
+  PreheaderBB->getTerminator()->setDebugLoc(
+                                      Header->getFirstNonPHI()->getDebugLoc());
+  DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
+               << PreheaderBB->getName() << "\n");
 
   // Make sure that NewBB is put someplace intelligent, which doesn't mess up
   // code layout too horribly.
-  PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
+  PlaceSplitBlockCarefully(PreheaderBB, OutsideBlocks, L);
 
-  return NewBB;
+  return PreheaderBB;
 }
 
 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
@@ -526,7 +536,17 @@ void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
 /// If we are able to separate out a loop, return the new outer loop that was
 /// created.
 ///
-Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
+Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM,
+                                       BasicBlock *Preheader) {
+  // Don't try to separate loops without a preheader (this excludes 
+  // loop headers which are targeted by an indirectbr).
+  if (!Preheader)
+    return 0;
+
+  // The header is not a landing pad; preheader insertion should ensure this.
+  assert(!L->getHeader()->isLandingPad() &&
+         "Can't insert backedge to landing pad");
+
   PHINode *PN = FindPHIToPartitionLoops(L, DT, AA, LI);
   if (PN == 0) return 0;  // No known way to partition.
 
@@ -536,13 +556,8 @@ Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
   SmallVector<BasicBlock*, 8> OuterLoopPreds;
   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
     if (PN->getIncomingValue(i) != PN ||
-        !L->contains(PN->getIncomingBlock(i))) {
-      // We can't split indirectbr edges.
-      if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
-        return 0;
-
+        !L->contains(PN->getIncomingBlock(i)))
       OuterLoopPreds.push_back(PN->getIncomingBlock(i));
-    }
 
   DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
 
@@ -636,6 +651,9 @@ LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
   if (!Preheader)
     return 0;
 
+  // The header is not a landing pad; preheader insertion should ensure this.
+  assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
+
   // Figure out which basic blocks contain back-edges to the loop header.
   std::vector<BasicBlock*> BackedgeBlocks;
   for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){