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LoopVectorize: PHIs with only outside users should prevent vectorization

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We check that instructions in the loop don't have outside users (except if
they are reduction values). Unfortunately, we skipped this check for
if-convertable PHIs.

Fixes PR16184.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183035 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnold Schwaighofer
2013-05-31 19:53:50 +00:00
parent 488401e9c9
commit 47afc19625
2 changed files with 71 additions and 13 deletions
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43
lib/Transforms/Vectorize/LoopVectorize.cpp
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@@ -2637,6 +2637,26 @@ static Type* getWiderType(DataLayout &DL, Type *Ty0, Type *Ty1) {
return Ty1;
}
/// \brief Check that the instruction has outside loop users and is not an
/// identified reduction variable.
static bool hasOutsideLoopUser(const Loop *TheLoop, Instruction *Inst,
SmallPtrSet<Value *, 4> &Reductions) {
// Reduction instructions are allowed to have exit users. All other
// instructions must not have external users.
if (!Reductions.count(Inst))
//Check that all of the users of the loop are inside the BB.
for (Value::use_iterator I = Inst->use_begin(), E = Inst->use_end();
I != E; ++I) {
Instruction *U = cast<Instruction>(*I);
// This user may be a reduction exit value.
if (!TheLoop->contains(U)) {
DEBUG(dbgs() << "LV: Found an outside user for : "<< *U << "\n");
return true;
}
}
return false;
}
bool LoopVectorizationLegality::canVectorizeInstrs() {
BasicBlock *PreHeader = TheLoop->getLoopPreheader();
BasicBlock *Header = TheLoop->getHeader();
@@ -2669,8 +2689,13 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
// If this PHINode is not in the header block, then we know that we
// can convert it to select during if-conversion. No need to check if
// the PHIs in this block are induction or reduction variables.
if (*bb != Header)
continue;
if (*bb != Header) {
// Check that this instruction has no outside users or is an
// identified reduction value with an outside user.
if(!hasOutsideLoopUser(TheLoop, it, AllowedExit))
continue;
return false;
}
// We only allow if-converted PHIs with more than two incoming values.
if (Phi->getNumIncomingValues() != 2) {
@@ -2769,17 +2794,9 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
// Reduction instructions are allowed to have exit users.
// All other instructions must not have external users.
if (!AllowedExit.count(it))
//Check that all of the users of the loop are inside the BB.
for (Value::use_iterator I = it->use_begin(), E = it->use_end();
I != E; ++I) {
Instruction *U = cast<Instruction>(*I);
// This user may be a reduction exit value.
if (!TheLoop->contains(U)) {
DEBUG(dbgs() << "LV: Found an outside user for : "<< *U << "\n");
return false;
}
}
if (hasOutsideLoopUser(TheLoop, it, AllowedExit))
return false;
} // next instr.
}