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[NFCI][GVN] Make IsValueFullyAvailableInBlock() readable - use enum class instead of magic numbers

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This does not change any logic, it only wraps the magic 0/1/2/3 constants
into an enum class.
This commit is contained in:
Roman Lebedev 2020-07-19 16:09:46 +03:00
parent cd1f19a232
commit 35029fb456
1 changed files with 41 additions and 24 deletions
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65
lib/Transforms/Scalar/GVN.cpp
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@ -667,6 +667,19 @@ LLVM_DUMP_METHOD void GVN::dump(DenseMap<uint32_t, Value*>& d) const {
}
#endif
enum class AvaliabilityState : char {
/// We know the block *is not* fully available. This is a fixpoint.
Unavaliable = 0,
/// We know the block *is* fully available. This is a fixpoint.
Avaliable = 1,
/// We do not know whether the block is fully available or not,
/// but we are currently speculating that it will be.
SpeculativelyAvaliable = 2,
/// We are speculating for this block and have used that
/// to speculate for other blocks.
SpeculativelyAvaliableAndUsedForSpeculation = 3,
};
/// Return true if we can prove that the value
/// we're analyzing is fully available in the specified block. As we go, keep
/// track of which blocks we know are fully alive in FullyAvailableBlocks. This
@ -677,24 +690,27 @@ LLVM_DUMP_METHOD void GVN::dump(DenseMap<uint32_t, Value*>& d) const {
/// currently speculating that it will be.
/// 3) we are speculating for this block and have used that to speculate for
/// other blocks.
static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
DenseMap<BasicBlock*, char> &FullyAvailableBlocks,
uint32_t RecurseDepth) {
static bool IsValueFullyAvailableInBlock(
BasicBlock *BB,
DenseMap<BasicBlock *, AvaliabilityState> &FullyAvailableBlocks,
uint32_t RecurseDepth) {
if (RecurseDepth > MaxRecurseDepth)
return false;
// Optimistically assume that the block is fully available and check to see
// if we already know about this block in one lookup.
std::pair<DenseMap<BasicBlock*, char>::iterator, bool> IV =
FullyAvailableBlocks.insert(std::make_pair(BB, 2));
// Optimistically assume that the block is speculatively available and check
// to see if we already know about this block in one lookup.
std::pair<DenseMap<BasicBlock *, AvaliabilityState>::iterator, bool> IV =
FullyAvailableBlocks.insert(
std::make_pair(BB, AvaliabilityState::SpeculativelyAvaliable));
// If the entry already existed for this block, return the precomputed value.
if (!IV.second) {
// If this is a speculative "available" value, mark it as being used for
// speculation of other blocks.
if (IV.first->second == 2)
IV.first->second = 3;
return IV.first->second != 0;
if (IV.first->second == AvaliabilityState::SpeculativelyAvaliable)
IV.first->second =
AvaliabilityState::SpeculativelyAvaliableAndUsedForSpeculation;
return IV.first->second != AvaliabilityState::Unavaliable;
}
// Otherwise, see if it is fully available in all predecessors.
@ -717,29 +733,30 @@ static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
// all, a fully-available block. We have a problem if we speculated on this and
// used the speculation to mark other blocks as available.
SpeculationFailure:
char &BBVal = FullyAvailableBlocks[BB];
AvaliabilityState &BBVal = FullyAvailableBlocks[BB];
// If we didn't speculate on this, just return with it set to false.
if (BBVal == 2) {
BBVal = 0;
// If we didn't speculate on this, just return with it set to unavaliable.
if (BBVal == AvaliabilityState::SpeculativelyAvaliable) {
BBVal = AvaliabilityState::Unavaliable;
return false;
}
// If we did speculate on this value, we could have blocks set to 1 that are
// incorrect. Walk the (transitive) successors of this block and mark them as
// 0 if set to one.
// If we did speculate on this value, we could have blocks set to
// speculatively avaliable that are incorrect. Walk the (transitive)
// successors of this block and mark them as unavaliable instead.
SmallVector<BasicBlock*, 32> BBWorklist;
BBWorklist.push_back(BB);
do {
BasicBlock *Entry = BBWorklist.pop_back_val();
// Note that this sets blocks to 0 (unavailable) if they happen to not
// Note that this sets blocks to unavailable if they happen to not
// already be in FullyAvailableBlocks. This is safe.
char &EntryVal = FullyAvailableBlocks[Entry];
if (EntryVal == 0) continue; // Already unavailable.
AvaliabilityState &EntryVal = FullyAvailableBlocks[Entry];
if (EntryVal == AvaliabilityState::Unavaliable)
continue; // Already unavailable.
// Mark as unavailable.
EntryVal = 0;
EntryVal = AvaliabilityState::Unavaliable;
BBWorklist.append(succ_begin(Entry), succ_end(Entry));
} while (!BBWorklist.empty());
@ -1107,11 +1124,11 @@ bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
// Check to see how many predecessors have the loaded value fully
// available.
MapVector<BasicBlock *, Value *> PredLoads;
DenseMap<BasicBlock*, char> FullyAvailableBlocks;
DenseMap<BasicBlock *, AvaliabilityState> FullyAvailableBlocks;
for (const AvailableValueInBlock &AV : ValuesPerBlock)
FullyAvailableBlocks[AV.BB] = true;
FullyAvailableBlocks[AV.BB] = AvaliabilityState::Avaliable;
for (BasicBlock *UnavailableBB : UnavailableBlocks)
FullyAvailableBlocks[UnavailableBB] = false;
FullyAvailableBlocks[UnavailableBB] = AvaliabilityState::Unavaliable;
SmallVector<BasicBlock *, 4> CriticalEdgePred;
for (BasicBlock *Pred : predecessors(LoadBB)) {