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Insert end_borrow for dead phi operands only when required

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DCE inserts end_borrow at phi operands when a guaranteed phi becomes dead.
This should be done for reborrows which end the lifetime of the incoming value.
The existing check was not accurate and ended up inserting end_borrow for forwarded values as well.

Fixes rdar://139283745
This commit is contained in:
Meghana Gupta
2024-11-12 12:44:00 -08:00
parent fa8852bf47
commit fd6d29d10b
2 changed files with 34 additions and 15 deletions
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30
lib/SILOptimizer/Transforms/DeadCodeElimination.cpp
View File

@@ -187,9 +187,8 @@ class DCE {
llvm::SmallPtrSetImpl<SILBasicBlock *> &);
SILBasicBlock *nearestUsefulPostDominator(SILBasicBlock *Block);
void replaceBranchWithJump(SILInstruction *Inst, SILBasicBlock *Block);
/// If \p value is live, insert a lifetime ending operation in ossa.
/// destroy_value for @owned value and end_borrow for a @guaranteed value.
void endLifetimeOfLiveValue(SILValue value, SILInstruction *insertPt);
/// Insert lifetime ending instruction if defining value of \p op is live.
void endLifetimeOfLiveValue(Operand *op, SILInstruction *insertPt);
public:
DCE(SILFunction *F, PostDominanceInfo *PDT)
@@ -585,7 +584,8 @@ void DCE::replaceBranchWithJump(SILInstruction *Inst, SILBasicBlock *Block) {
(void)Branch;
}
void DCE::endLifetimeOfLiveValue(SILValue value, SILInstruction *insertPt) {
void DCE::endLifetimeOfLiveValue(Operand *op, SILInstruction *insertPt) {
auto value = op->get();
if (SILInstruction *inst = value->getDefiningInstruction()) {
if (!LiveInstructions.contains(inst))
return;
@@ -593,15 +593,15 @@ void DCE::endLifetimeOfLiveValue(SILValue value, SILInstruction *insertPt) {
if (!LiveArguments.contains(arg))
return;
}
assert(op->isLifetimeEnding());
SILBuilderWithScope builder(insertPt);
if (value->getOwnershipKind() == OwnershipKind::Owned) {
builder.emitDestroyOperation(RegularLocation::getAutoGeneratedLocation(),
builder.createDestroyValue(RegularLocation::getAutoGeneratedLocation(),
value);
}
BorrowedValue borrow(lookThroughBorrowedFromDef(value));
if (borrow && borrow.isLocalScope()) {
builder.emitEndBorrowOperation(RegularLocation::getAutoGeneratedLocation(),
value);
if (value->getOwnershipKind() == OwnershipKind::Guaranteed) {
builder.createEndBorrow(RegularLocation::getAutoGeneratedLocation(), value);
}
}
@@ -657,7 +657,7 @@ bool DCE::removeDead() {
for (auto *pred : BB.getPredecessorBlocks()) {
auto *predTerm = pred->getTerminator();
SILInstruction *insertPt = predTerm;
if (phiArg->getOwnershipKind() == OwnershipKind::Guaranteed) {
if (phiArg->isReborrow()) {
// If the phiArg is dead and had reborrow dependencies, its baseValue
// may also have been dead and a destroy_value of its baseValue may
// have been inserted before the pred's terminator. Make sure to
@@ -677,8 +677,10 @@ bool DCE::removeDead() {
insertPt = &predInst;
}
}
endLifetimeOfLiveValue(phiArg->getIncomingPhiValue(pred), insertPt);
auto *predOp = phiArg->getIncomingPhiOperand(pred);
if (predOp->isLifetimeEnding()) {
endLifetimeOfLiveValue(predOp, insertPt);
}
}
erasePhiArgument(&BB, i, /*cleanupDeadPhiOps=*/true,
InstModCallbacks().onCreateNewInst(
@@ -702,7 +704,7 @@ bool DCE::removeDead() {
for (auto &op : termInst->getAllOperands()) {
if (op.isLifetimeEnding()) {
endLifetimeOfLiveValue(op.get(), termInst);
endLifetimeOfLiveValue(&op, termInst);
}
}
LLVM_DEBUG(llvm::dbgs() << "Replacing branch: ");
@@ -725,7 +727,7 @@ bool DCE::removeDead() {
if (F->hasOwnership()) {
for (auto &Op : Inst->getAllOperands()) {
if (Op.isLifetimeEnding()) {
endLifetimeOfLiveValue(Op.get(), Inst);
endLifetimeOfLiveValue(&Op, Inst);
}
}
}

17
test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil
View File

@@ -1220,3 +1220,20 @@ bb0:
return %t : $()
}
// CHECK-LABEL: sil [ossa] @dce_dead_guaranteedphi :
// bb2:
// CHECK-LABEL: } // end sil function 'dce_dead_guaranteedphi'
sil [ossa] @dce_dead_guaranteedphi : $@convention(thin) (@owned NonTrivialStruct) -> () {
bb0(%0 : @owned $NonTrivialStruct):
%b = begin_borrow %0 : $NonTrivialStruct
%func = function_ref @$use_nontrivialstruct2 : $@convention(thin) (@guaranteed NonTrivialStruct) -> ()
%funcres = apply %func(%b) : $@convention(thin) (@guaranteed NonTrivialStruct) -> ()
br bb2(%b : $NonTrivialStruct, %b : $NonTrivialStruct)
bb2(%phi1 : @guaranteed $NonTrivialStruct, %phi2 : @guaranteed $NonTrivialStruct):
end_borrow %phi1 : $NonTrivialStruct
destroy_value %0 : $NonTrivialStruct
%9999 = tuple()
return %9999 : $()
}