Handle Top-Level-Regions in polly::isHoistableLoad

Summary:
This can be seen as a follow-up on my previous differential [D33411](https://reviews.llvm.org/D33411).
We received a bug report where this error was triggered. I have tried my best to recreate the issue in a minimal lit testcase which is also part of this differential.

I only handle return instructions as predecessors to a virtual TLR-exit right now. From inspecting the codebase, it seems `unreachable` instructions may also be of interest here. If requested, I can extend my patches to consider them as well. I would also apply this on `ScopHelper.cpp::isErrorBlock` (see D33411), of course.

Reviewers: philip.pfaffe, bollu

Reviewed By: bollu

Subscribers: Meinersbur, pollydev, llvm-commits

Tags: #polly

Differential Revision: https://reviews.llvm.org/D40492

llvm-svn: 319431

1 files changed, 9 insertions, 3 deletions

diff --git a/polly/lib/Support/ScopHelper.cpp b/polly/lib/Support/ScopHelper.cpp
index ac501113d8d..87ac658a79d 100644
--- a/polly/lib/Support/ScopHelper.cpp
+++ b/polly/lib/Support/ScopHelper.cpp
@@ -473,9 +473,15 @@ bool polly::isHoistableLoad(LoadInst *LInst, Region &R, LoopInfo &LI,
       return false;
 
     bool DominatesAllPredecessors = true;
-    for (auto Pred : predecessors(R.getExit()))
-      if (R.contains(Pred) && !DT.dominates(&BB, Pred))
-        DominatesAllPredecessors = false;
+    if (R.isTopLevelRegion()) {
+      for (BasicBlock &I : *R.getEntry()->getParent())
+        if (isa<ReturnInst>(I.getTerminator()) && !DT.dominates(&BB, &I))
+          DominatesAllPredecessors = false;
+    } else {
+      for (auto Pred : predecessors(R.getExit()))
+        if (R.contains(Pred) && !DT.dominates(&BB, Pred))
+          DominatesAllPredecessors = false;
+    }
 
     if (!DominatesAllPredecessors)
       continue;