ScopDetection: Tighten the check for always executed 'error blocks'

Basic blocks that are always executed can not be error blocks as their execution
can not possibly be an unlikely event. In this commit we tighten the check
if an error block to basic blcoks that do not dominate the exit condition, but
that dominate all exiting blocks of the scop.

llvm-svn: 252726

1 files changed, 8 insertions, 1 deletions

diff --git a/polly/lib/Support/ScopHelper.cpp b/polly/lib/Support/ScopHelper.cpp
index 49e1e9eab17..777eb9b518a 100644
--- a/polly/lib/Support/ScopHelper.cpp
+++ b/polly/lib/Support/ScopHelper.cpp
@@ -352,7 +352,14 @@ bool polly::isErrorBlock(BasicBlock &BB, const Region &R, LoopInfo &LI,
   if (LI.isLoopHeader(&BB))
     return false;
 
-  if (DT.dominates(&BB, R.getExit()))
+  // Basic blocks that are always executed are not considered error blocks,
+  // as their execution can not be a rare event.
+  bool DominatesAllPredecessors = true;
+  for (auto Pred : predecessors(R.getExit()))
+    if (R.contains(Pred) && !DT.dominates(&BB, Pred))
+      DominatesAllPredecessors = false;
+
+  if (DominatesAllPredecessors)
     return false;
 
   // FIXME: This is a simple heuristic to determine if the load is executed