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LoopVectorizer: Don't if-convert constant expressions that can trap

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A phi node operand or an instruction operand could be a constant expression that
can trap (division). Check that we don't vectorize such cases.

PR16729
radar://15653590

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197449 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer
2013-12-17 01:11:01 +00:00
parent a6380c22e4
commit 83196a9fcb
2 changed files with 94 additions and 1 deletions
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32
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -2804,6 +2804,23 @@ void InnerLoopVectorizer::updateAnalysis() {
DEBUG(DT->verifyAnalysis());
}
/// \brief Check whether it is safe to if-convert this phi node.
///
/// Phi nodes with constant expressions that can trap are not safe to if
/// convert.
static bool canIfConvertPHINodes(BasicBlock *BB) {
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
PHINode *Phi = dyn_cast<PHINode>(I);
if (!Phi)
return true;
for (unsigned p = 0, e = Phi->getNumIncomingValues(); p != e; ++p)
if (Constant *C = dyn_cast<Constant>(Phi->getIncomingValue(p)))
if (C->canTrap())
return false;
}
return true;
}
bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
if (!EnableIfConversion)
return false;
@ -2830,6 +2847,7 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
}
// Collect the blocks that need predication.
BasicBlock *Header = TheLoop->getHeader();
for (Loop::block_iterator BI = TheLoop->block_begin(),
BE = TheLoop->block_end(); BI != BE; ++BI) {
BasicBlock *BB = *BI;
@ -2839,8 +2857,12 @@ bool LoopVectorizationLegality::canVectorizeWithIfConvert() {
return false;
// We must be able to predicate all blocks that need to be predicated.
if (blockNeedsPredication(BB) && !blockCanBePredicated(BB, SafePointes))
if (blockNeedsPredication(BB)) {
if (!blockCanBePredicated(BB, SafePointes))
return false;
} else if (BB != Header && !canIfConvertPHINodes(BB))
return false;
}
// We can if-convert this loop.
@ -4394,6 +4416,14 @@ bool LoopVectorizationLegality::blockCanBePredicated(BasicBlock *BB,
if (it->mayWriteToMemory() || it->mayThrow())
return false;
// Check that we don't have a constant expression that can trap as operand.
for (Instruction::op_iterator OI = it->op_begin(), OE = it->op_end();
OI != OE; ++OI) {
if (Constant *C = dyn_cast<Constant>(*OI))
if (C->canTrap())
return false;
}
// The instructions below can trap.
switch (it->getOpcode()) {
default: continue;