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[DSE] Hoist partial store merging code into function (NFC).

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Hoist the general logic into a new function, because it can be re-used
by the MemorySSA backed DSE as well.
This commit is contained in:
Florian Hahn 2020-06-15 15:37:33 +01:00
parent 36ed6c0076
commit bf411cb019
1 changed files with 50 additions and 44 deletions
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94
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -1150,6 +1150,52 @@ static bool eliminateNoopStore(Instruction *Inst, BasicBlock::iterator &BBI,
return false;
}
static Constant *
tryToMergePartialOverlappingStores(StoreInst *Earlier, StoreInst *Later,
int64_t InstWriteOffset,
int64_t DepWriteOffset, const DataLayout &DL,
AliasAnalysis *AA, DominatorTree *DT) {
if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) &&
DL.typeSizeEqualsStoreSize(Earlier->getValueOperand()->getType()) &&
Later && isa<ConstantInt>(Later->getValueOperand()) &&
DL.typeSizeEqualsStoreSize(Later->getValueOperand()->getType()) &&
memoryIsNotModifiedBetween(Earlier, Later, AA, DL, DT)) {
// If the store we find is:
// a) partially overwritten by the store to 'Loc'
// b) the later store is fully contained in the earlier one and
// c) they both have a constant value
// d) none of the two stores need padding
// Merge the two stores, replacing the earlier store's value with a
// merge of both values.
// TODO: Deal with other constant types (vectors, etc), and probably
// some mem intrinsics (if needed)
APInt EarlierValue =
cast<ConstantInt>(Earlier->getValueOperand())->getValue();
APInt LaterValue = cast<ConstantInt>(Later->getValueOperand())->getValue();
unsigned LaterBits = LaterValue.getBitWidth();
assert(EarlierValue.getBitWidth() > LaterValue.getBitWidth());
LaterValue = LaterValue.zext(EarlierValue.getBitWidth());
// Offset of the smaller store inside the larger store
unsigned BitOffsetDiff = (InstWriteOffset - DepWriteOffset) * 8;
unsigned LShiftAmount = DL.isBigEndian() ? EarlierValue.getBitWidth() -
BitOffsetDiff - LaterBits
: BitOffsetDiff;
APInt Mask = APInt::getBitsSet(EarlierValue.getBitWidth(), LShiftAmount,
LShiftAmount + LaterBits);
// Clear the bits we'll be replacing, then OR with the smaller
// store, shifted appropriately.
APInt Merged = (EarlierValue & ~Mask) | (LaterValue << LShiftAmount);
LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Earlier: " << *Earlier
<< "\n Later: " << *Later
<< "\n Merged Value: " << Merged << '\n');
return ConstantInt::get(Earlier->getValueOperand()->getType(), Merged);
}
return nullptr;
}
static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
MemoryDependenceResults *MD, DominatorTree *DT,
const TargetLibraryInfo *TLI) {
@ -1297,51 +1343,11 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
OR == OW_PartialEarlierWithFullLater) {
auto *Earlier = dyn_cast<StoreInst>(DepWrite);
auto *Later = dyn_cast<StoreInst>(Inst);
if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) &&
DL.typeSizeEqualsStoreSize(
Earlier->getValueOperand()->getType()) &&
Later && isa<ConstantInt>(Later->getValueOperand()) &&
DL.typeSizeEqualsStoreSize(
Later->getValueOperand()->getType()) &&
memoryIsNotModifiedBetween(Earlier, Later, AA, DL, DT)) {
// If the store we find is:
// a) partially overwritten by the store to 'Loc'
// b) the later store is fully contained in the earlier one and
// c) they both have a constant value
// d) none of the two stores need padding
// Merge the two stores, replacing the earlier store's value with a
// merge of both values.
// TODO: Deal with other constant types (vectors, etc), and probably
// some mem intrinsics (if needed)
APInt EarlierValue =
cast<ConstantInt>(Earlier->getValueOperand())->getValue();
APInt LaterValue =
cast<ConstantInt>(Later->getValueOperand())->getValue();
unsigned LaterBits = LaterValue.getBitWidth();
assert(EarlierValue.getBitWidth() > LaterValue.getBitWidth());
LaterValue = LaterValue.zext(EarlierValue.getBitWidth());
// Offset of the smaller store inside the larger store
unsigned BitOffsetDiff = (InstWriteOffset - DepWriteOffset) * 8;
unsigned LShiftAmount =
DL.isBigEndian()
? EarlierValue.getBitWidth() - BitOffsetDiff - LaterBits
: BitOffsetDiff;
APInt Mask =
APInt::getBitsSet(EarlierValue.getBitWidth(), LShiftAmount,
LShiftAmount + LaterBits);
// Clear the bits we'll be replacing, then OR with the smaller
// store, shifted appropriately.
APInt Merged =
(EarlierValue & ~Mask) | (LaterValue << LShiftAmount);
LLVM_DEBUG(dbgs() << "DSE: Merge Stores:\n Earlier: " << *DepWrite
<< "\n Later: " << *Inst
<< "\n Merged Value: " << Merged << '\n');
if (Constant *C = tryToMergePartialOverlappingStores(
Earlier, Later, InstWriteOffset, DepWriteOffset, DL, AA,
DT)) {
auto *SI = new StoreInst(
ConstantInt::get(Earlier->getValueOperand()->getType(), Merged),
Earlier->getPointerOperand(), false, Earlier->getAlign(),
C, Earlier->getPointerOperand(), false, Earlier->getAlign(),
Earlier->getOrdering(), Earlier->getSyncScopeID(), DepWrite);
unsigned MDToKeep[] = {LLVMContext::MD_dbg, LLVMContext::MD_tbaa,