Introduce splitBlock and use it in splitEntryBlockForAlloca

RegionInfo::splitBlock did not update RegionInfo correctly. Specifically, it tried to make the new block the entry block if possible. This breaks for nested regions that have edges to the old block. 

We simply do not change the entry block. Updating RegionInfo becomes trivial as both block will always be in the same region.

splitEntryBlockForAlloca makes use of the new splitBlock.

Reviewers: grosser

Part of Differential Revision: http://reviews.llvm.org/D11867

llvm-svn: 244600

1 files changed, 36 insertions, 4 deletions

diff --git a/polly/lib/Support/ScopHelper.cpp b/polly/lib/Support/ScopHelper.cpp
index 176b30da65b..633f74bfe9a 100644
--- a/polly/lib/Support/ScopHelper.cpp
+++ b/polly/lib/Support/ScopHelper.cpp
@@ -169,6 +169,38 @@ BasicBlock *polly::simplifyRegion(Scop *S, Pass *P) {
   return EnteringBB;
 }
 
+// Split the block into two successive blocks.
+//
+// Like llvm::SplitBlock, but also preserves RegionInfo
+static BasicBlock *splitBlock(BasicBlock *Old, Instruction *SplitPt,
+                              DominatorTree *DT, llvm::LoopInfo *LI,
+                              RegionInfo *RI) {
+  assert(Old && SplitPt);
+
+  // Before:
+  //
+  //  \   /  //
+  //   Old   //
+  //  /   \  //
+
+  BasicBlock *NewBlock = llvm::SplitBlock(Old, SplitPt, DT, LI);
+
+  if (RI) {
+    Region *R = RI->getRegionFor(Old);
+    RI->setRegionFor(NewBlock, R);
+  }
+
+  // After:
+  //
+  //   \   /    //
+  //    Old     //
+  //     |      //
+  //  NewBlock  //
+  //   /   \    //
+
+  return NewBlock;
+}
+
 void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, Pass *P) {
   // Find first non-alloca instruction. Every basic block has a non-alloc
   // instruction, as every well formed basic block has a terminator.
@@ -180,9 +212,9 @@ void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, Pass *P) {
   auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
   auto *LIWP = P->getAnalysisIfAvailable<LoopInfoWrapperPass>();
   auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
+  RegionInfoPass *RIP = P->getAnalysisIfAvailable<RegionInfoPass>();
+  RegionInfo *RI = RIP ? &RIP->getRegionInfo() : nullptr;
 
-  // SplitBlock updates DT, DF and LI.
-  BasicBlock *NewEntry = SplitBlock(EntryBlock, I, DT, LI);
-  if (RegionInfoPass *RIP = P->getAnalysisIfAvailable<RegionInfoPass>())
-    RIP->getRegionInfo().splitBlock(NewEntry, EntryBlock);
+  // splitBlock updates DT, LI and RI.
+  splitBlock(EntryBlock, I, DT, LI, RI);
 }