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LoopVectorizer: Fix a dominance issue

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The induction variables start value needs to be defined before we branch
(overflow check) to the scalar preheader where we used it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211460 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer
2014-06-22 03:38:59 +00:00
parent c815039ca2
commit 78f173a22d
2 changed files with 51 additions and 8 deletions
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25
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -1987,10 +1987,6 @@ void InnerLoopVectorizer::createEmptyLoop() {
Constant::getAllOnesValue(BackedgeCount->getType()),
"backedge.overflow", BypassBlock->getTerminator());
// Count holds the overall loop count (N).
Value *Count = Exp.expandCodeFor(ExitCount, ExitCount->getType(),
BypassBlock->getTerminator());
// The loop index does not have to start at Zero. Find the original start
// value from the induction PHI node. If we don't have an induction variable
// then we know that it starts at zero.
@ -2000,6 +1996,18 @@ void InnerLoopVectorizer::createEmptyLoop() {
IdxTy):
ConstantInt::get(IdxTy, 0);
// We need an instruction to anchor the overflow check on. StartIdx needs to
// be defined before the overflow check branch. Because the scalar preheader
// is going to merge the start index and so the overflow branch block needs to
// contain a definition of the start index.
Instruction *OverflowCheckAnchor = BinaryOperator::CreateAdd(
StartIdx, ConstantInt::get(IdxTy, 0), "overflow.check.anchor",
BypassBlock->getTerminator());
// Count holds the overall loop count (N).
Value *Count = Exp.expandCodeFor(ExitCount, ExitCount->getType(),
BypassBlock->getTerminator());
LoopBypassBlocks.push_back(BypassBlock);
// Split the single block loop into the two loop structure described above.
@ -2068,17 +2076,18 @@ void InnerLoopVectorizer::createEmptyLoop() {
// Now, compare the new count to zero. If it is zero skip the vector loop and
// jump to the scalar loop.
Value *Cmp = BypassBuilder.CreateICmpEQ(IdxEndRoundDown, StartIdx,
"cmp.zero");
Value *Cmp =
BypassBuilder.CreateICmpEQ(IdxEndRoundDown, StartIdx, "cmp.zero");
BasicBlock *LastBypassBlock = BypassBlock;
// Generate code to check that the loops trip count that we computed by adding
// one to the backedge-taken count will not overflow.
{
auto PastOverflowCheck = std::next(BasicBlock::iterator(CheckBCOverflow));
auto PastOverflowCheck =
std::next(BasicBlock::iterator(OverflowCheckAnchor));
BasicBlock *CheckBlock =
LastBypassBlock->splitBasicBlock(PastOverflowCheck, "overflow.checked");
LastBypassBlock->splitBasicBlock(PastOverflowCheck, "overflow.checked");
if (ParentLoop)
ParentLoop->addBasicBlockToLoop(CheckBlock, LI->getBase());
LoopBypassBlocks.push_back(CheckBlock);