Teach SplitBlockPredecessors how to handle landingpad blocks.

Patch by: Igor Laevsky <igor@azulsystems.com>

"Currently SplitBlockPredecessors generates incorrect code in case if basic block we are going to split has a landingpad. Also seems like it is fairly common case among it's users to conditionally call either SplitBlockPredecessors or SplitLandingPadPredecessors. Because of this I think it is reasonable to add this condition directly into SplitBlockPredecessors."

Differential Revision: http://reviews.llvm.org/D7157

llvm-svn: 227390

llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h

@@ -202,11 +202,15 @@ BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To,
 BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt,
                        DominatorTree *DT = nullptr, LoopInfo *LI = nullptr);
 
-/// SplitBlockPredecessors - This method transforms BB by introducing a new
-/// basic block into the function, and moving some of the predecessors of BB to
-/// be predecessors of the new block.  The new predecessors are indicated by the
-/// Preds array, which has NumPreds elements in it.  The new block is given a
-/// suffix of 'Suffix'.  This function returns the new block.
+/// SplitBlockPredecessors - This method introduces at least one new basic block
+/// into the function and moves some of the predecessors of BB to be
+/// predecessors of the new block. The new predecessors are indicated by the
+/// Preds array. The new block is given a suffix of 'Suffix'. Returns new basic
+/// block to which predecessors from Preds are now pointing.
+///
+/// If BB is a landingpad block then additional basicblock might be introduced.
+/// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more
+/// details on this case.
 ///
 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.

llvm/lib/Transforms/Scalar/LoopUnswitch.cpp

@@ -769,16 +769,9 @@ void LoopUnswitch::SplitExitEdges(Loop *L,
 
     // Although SplitBlockPredecessors doesn't preserve loop-simplify in
     // general, if we call it on all predecessors of all exits then it does.
-    if (!ExitBlock->isLandingPad()) {
-      SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa",
-                             /*AliasAnalysis*/ nullptr, DT, LI,
-                             /*PreserveLCSSA*/ true);
-    } else {
-      SmallVector<BasicBlock*, 2> NewBBs;
-      SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
-                                  NewBBs, /*AliasAnalysis*/ nullptr, DT, LI,
-                                  /*PreserveLCSSA*/ true);
-    }
+    SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa",
+                           /*AliasAnalysis*/ nullptr, DT, LI,
+                           /*PreserveLCSSA*/ true);
   }
 }
 

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -454,11 +454,15 @@ static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
   }
 }
 
-/// SplitBlockPredecessors - This method transforms BB by introducing a new
-/// basic block into the function, and moving some of the predecessors of BB to
-/// be predecessors of the new block.  The new predecessors are indicated by the
-/// Preds array, which has NumPreds elements in it.  The new block is given a
-/// suffix of 'Suffix'.
+/// SplitBlockPredecessors - This method introduces at least one new basic block
+/// into the function and moves some of the predecessors of BB to be
+/// predecessors of the new block. The new predecessors are indicated by the
+/// Preds array. The new block is given a suffix of 'Suffix'. Returns new basic
+/// block to which predecessors from Preds are now pointing.
+///
+/// If BB is a landingpad block then additional basicblock might be introduced.
+/// It will have suffix of 'Suffix'+".split_lp".
+/// See SplitLandingPadPredecessors for more details on this case.
 ///
 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
 /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
@@ -470,6 +474,17 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
                                          const char *Suffix, AliasAnalysis *AA,
                                          DominatorTree *DT, LoopInfo *LI,
                                          bool PreserveLCSSA) {
+  // For the landingpads we need to act a bit differently.
+  // Delegate this work to the SplitLandingPadPredecessors.
+  if (BB->isLandingPad()) {
+    SmallVector<BasicBlock*, 2> NewBBs;
+    std::string NewName = std::string(Suffix) + ".split-lp";
+
+    SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(),
+                                NewBBs, AA, DT, LI, PreserveLCSSA);
+    return NewBBs[0];
+  }
+
   // Create new basic block, insert right before the original block.
   BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
                                          BB->getParent(), BB);

llvm/lib/Transforms/Utils/LoopSimplify.cpp

@@ -139,15 +139,8 @@ BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) {
 
   // Split out the loop pre-header.
   BasicBlock *PreheaderBB;
-  if (!Header->isLandingPad()) {
-    PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
-                                         AA, DT, LI, PreserveLCSSA);
-  } else {
-    SmallVector<BasicBlock*, 2> NewBBs;
-    SplitLandingPadPredecessors(Header, OutsideBlocks, ".preheader",
-                                ".split-lp", NewBBs, AA, DT, LI, PreserveLCSSA);
-    PreheaderBB = NewBBs[0];
-  }
+  PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
+                                       AA, DT, LI, PreserveLCSSA);
 
   PreheaderBB->getTerminator()->setDebugLoc(
                                       Header->getFirstNonPHI()->getDebugLoc());
@@ -184,15 +177,8 @@ static BasicBlock *rewriteLoopExitBlock(Loop *L, BasicBlock *Exit,
 
   bool PreserveLCSSA = PP->mustPreserveAnalysisID(LCSSAID);
 
-  if (Exit->isLandingPad()) {
-    SmallVector<BasicBlock*, 2> NewBBs;
-    SplitLandingPadPredecessors(Exit, LoopBlocks, ".loopexit", ".nonloopexit",
-                                NewBBs, AA, DT, LI, PreserveLCSSA);
-    NewExitBB = NewBBs[0];
-  } else {
-    NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", AA, DT,
-                                       LI, PreserveLCSSA);
-  }
+  NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", AA, DT,
+                                     LI, PreserveLCSSA);
 
   DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
                << NewExitBB->getName() << "\n");

llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp

@@ -119,15 +119,8 @@ static void ConnectProlog(Loop *L, Value *TripCount, unsigned Count,
   assert(Exit && "Loop must have a single exit block only");
   // Split the exit to maintain loop canonicalization guarantees
   SmallVector<BasicBlock*, 4> Preds(pred_begin(Exit), pred_end(Exit));
-  if (!Exit->isLandingPad()) {
-    SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", AA, DT, LI,
-                           P->mustPreserveAnalysisID(LCSSAID));
-  } else {
-    SmallVector<BasicBlock*, 2> NewBBs;
-    SplitLandingPadPredecessors(Exit, Preds, ".unr1-lcssa", ".unr2-lcssa",
-                                NewBBs, AA, DT, LI,
-                                P->mustPreserveAnalysisID(LCSSAID));
-  }
+  SplitBlockPredecessors(Exit, Preds, ".unr-lcssa", AA, DT, LI,
+                         P->mustPreserveAnalysisID(LCSSAID));
   // Add the branch to the exit block (around the unrolled loop)
   BranchInst::Create(Exit, NewPH, BrLoopExit, InsertPt);
   InsertPt->eraseFromParent();

llvm/test/Transforms/LoopSimplify/2011-12-14-LandingpadHeader.ll

@@ -12,7 +12,7 @@ entry:
 ; CHECK-NEXT: landingpad
 ; CHECK: br label %catch
 
-; CHECK: catch.split-lp:
+; CHECK: catch.preheader.split-lp:
 ; CHECK-NEXT: landingpad
 ; CHECK: br label %catch