PR14448 - prevent the loop vectorizer from vectorizing the same loop twice.

[oota-llvm.git] / lib / Transforms / Vectorize / LoopVectorize.cpp

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index ef9c7c9db2e98ed8e76d30b34b3cd868a6517c8d..0d11372808456318d5e467323f9b00d72fa12406 100644 (file)
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -116,6 +116,12 @@ static const unsigned TinyTripCountUnrollThreshold = 128;
 /// number of pointers. Notice that the check is quadratic!
 static const unsigned RuntimeMemoryCheckThreshold = 4;
 
+/// We use a metadata with this name  to indicate that a scalar loop was
+/// vectorized and that we don't need to re-vectorize it if we run into it
+/// again.
+static const char*
+AlreadyVectorizedMDName = "llvm.vectorizer.already_vectorized";
+
 namespace {
 
 // Forward declarations.
@@ -1159,6 +1165,11 @@ InnerLoopVectorizer::createEmptyLoop(LoopVectorizationLegality *Legal) {
   BasicBlock *ExitBlock = OrigLoop->getExitBlock();
   assert(ExitBlock && "Must have an exit block");
 
+  // Mark the old scalar loop with metadata that tells us not to vectorize this
+  // loop again if we run into it.
+  MDNode *MD = MDNode::get(OldBasicBlock->getContext(), ArrayRef<Value*>());
+  OldBasicBlock->getTerminator()->setMetadata(AlreadyVectorizedMDName, MD);
+
   // Some loops have a single integer induction variable, while other loops
   // don't. One example is c++ iterators that often have multiple pointer
   // induction variables. In the code below we also support a case where we
@@ -2224,6 +2235,13 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
   BasicBlock *PreHeader = TheLoop->getLoopPreheader();
   BasicBlock *Header = TheLoop->getHeader();
 
+  // If we marked the scalar loop as "already vectorized" then no need
+  // to vectorize it again.
+  if (Header->getTerminator()->getMetadata(AlreadyVectorizedMDName)) {
+    DEBUG(dbgs() << "LV: This loop was vectorized before\n");
+    return false;
+  }
+
   // For each block in the loop.
   for (Loop::block_iterator bb = TheLoop->block_begin(),
        be = TheLoop->block_end(); bb != be; ++bb) {