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Fix DCE of begin_borrow with @guaranteed operand

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For the lower most begin_borrows with @guaranteed operands, there
was no @guaranteed phi computation, restructure the code and fix this case.
This commit is contained in:
Meghana Gupta
2023-01-05 20:11:25 -08:00
parent 0144fb6eea
commit cdeb55a20a
2 changed files with 57 additions and 19 deletions
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34
lib/SILOptimizer/Transforms/DeadCodeElimination.cpp
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@@ -283,37 +283,33 @@ void DCE::markLive() {
break;
}
case SILInstructionKind::BeginBorrowInst: {
// Currently we only support borrows of owned values.
// Nested borrow handling can be complex in the presence of reborrows.
// So it is not handled currently.
auto *borrowInst = cast<BeginBorrowInst>(&I);
// Populate guaranteedPhiDependencies for this borrowInst
findGuaranteedPhiDependencies(BorrowedValue(borrowInst));
auto disableBorrowDCE = [&](SILValue borrow) {
visitTransitiveEndBorrows(borrow, [&](EndBorrowInst *endBorrow) {
markInstructionLive(endBorrow);
});
};
// If we have a begin_borrow of a @guaranteed operand, disable DCE'ing
// of parent borrow scopes. Dead reborrows needs complex handling, whuch
// is why it is disabled for now.
if (borrowInst->getOperand()->getOwnershipKind() ==
OwnershipKind::Guaranteed) {
// Visit the end_borrows of all the borrow scopes that this
// begin_borrow could be borrowing.
SmallVector<SILValue, 4> roots;
findGuaranteedReferenceRoots(borrowInst->getOperand(),
/*lookThroughNestedBorrows=*/false,
roots);
// Visit the end_borrows of all the borrow scopes that this
// begin_borrow could be borrowing, and mark them live.
for (auto root : roots) {
visitTransitiveEndBorrows(root,
[&](EndBorrowInst *endBorrow) {
markInstructionLive(endBorrow);
});
disableBorrowDCE(root);
}
continue;
}
// Populate guaranteedPhiDependencies for this borrow
findGuaranteedPhiDependencies(BorrowedValue(borrowInst));
// Don't optimize a borrow scope if it is lexical or has a pointer
// escape.
// If we have a lexical borrow scope or a pointer escape, disable DCE.
if (borrowInst->isLexical() ||
hasPointerEscape(BorrowedValue(borrowInst))) {
// Visit all end_borrows and mark them live
visitTransitiveEndBorrows(borrowInst, [&](EndBorrowInst *endBorrow) {
markInstructionLive(endBorrow);
});
continue;
disableBorrowDCE(borrowInst);
}
break;
}