From f9b5954255fa3dca6de150affb48d8729fbb1c22 Mon Sep 17 00:00:00 2001 From: dim Date: Tue, 9 Dec 2014 07:48:25 +0000 Subject: 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 Note: because this is applied on top of llvm/clang 3.5.0, this fix is slightly different from the one just checked into head in r275633. --- contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp') diff --git a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp index 531d349..c1e8df9 100644 --- a/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp +++ b/contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp @@ -3466,6 +3466,15 @@ bool LoopVectorizationLegality::canVectorize() { 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()) { + emitAnalysis( + Report() << "loop control flow is not understood by vectorizer"); + return false; + } + // We need to have a loop header. DEBUG(dbgs() << "LV: Found a loop: " << TheLoop->getHeader()->getName() << '\n'); -- cgit v1.1