Pull in r223171 from upstream llvm trunk (by Michael Zolotukhin):

  PR21302. Vectorize only bottom-tested loops.

  rdar://problem/18886083

This fixes a bug in the llvm vectorizer, which could sometimes cause
vectorized loops to perform an additional iteration, leading to possible
buffer overruns.  Symptoms of this, which are usually segfaults, were
first noticed when building gcc ports, here:

https://lists.freebsd.org/pipermail/freebsd-ports/2014-September/095466.html
https://lists.freebsd.org/pipermail/freebsd-toolchain/2014-September/001211.html

Since this fix is very important for ports, bump __FreeBSD_version to
make it easier for port maintainers to test whether the fix has been
applied.

Upstream PR:	http://llvm.org/PR21302
MFC after:	3 days

1 files changed, 8 insertions, 0 deletions

diff --git a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index f9f6b18..6a9b9dc 100644
--- a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2864,6 +2864,14 @@ bool LoopVectorizationLegality::canVectorize() {
   if (!TheLoop->getExitingBlock())
     return false;
 
+  // We only handle bottom-tested loops, i.e. loop in which the condition is
+  // checked at the end of each iteration. With that we can assume that all
+  // instructions in the loop are executed the same number of times.
+  if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
+    DEBUG(dbgs() << "LV: loop control flow is not understood by vectorizer\n");
+    return false;
+  }
+
   // We need to have a loop header.
   DEBUG(dbgs() << "LV: Found a loop: " <<
         TheLoop->getHeader()->getName() << '\n');