Check for an empty error log.

Fixes #19976.

The error log does not contain an error, in case we reject a candidate
without generating a diagnostic message by using invalid<>(...). This is
the case for the top-level region of a function.

The patch comes without a test-case because adding a useful one requires
additional code just for triggering it. Before the patch it would only trigger,
if we try to print the CFG with Scop error annotations.

llvm-svn: 210753

1 files changed, 8 insertions, 1 deletions

diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index 8a9226e6331..f1fafaabd58 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -219,7 +219,14 @@ std::string ScopDetection::regionIsInvalidBecause(const Region *R) const {
   // Get the first error we found. Even in keep-going mode, this is the first
   // reason that caused the candidate to be rejected.
   RejectLog Errors = RejectLogs.at(R);
-  return (*Errors.begin())->getMessage();
+
+  // This can happen when we marked a region invalid, but didn't track
+  // an error for it.
+  if (Errors.size() == 0)
+    return "";
+
+  RejectReasonPtr RR = *Errors.begin();
+  return RR->getMessage();
 }
 
 bool ScopDetection::isValidCFG(BasicBlock &BB,