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//===--- BorrowScopeOpts.cpp ----------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
///
/// \file
///
/// Optimizations that attempt to simplify and or eliminate borrow scopes. Today
/// we only eliminate scopes, but we could also eliminate redundant scopes by
/// converting struct_extract operations to use destructure operations.
///
//===----------------------------------------------------------------------===//
#include "Context.h"
#include "SemanticARCOptVisitor.h"
using namespace swift;
using namespace swift::semanticarc;
bool SemanticARCOptVisitor::visitBeginBorrowInst(BeginBorrowInst *bbi) {
// Quickly check if we are supposed to perform this transformation.
if (!ctx.shouldPerform(ARCTransformKind::RedundantBorrowScopeElimPeephole))
return false;
// Non-redundant, lexical borrow scopes must remain in order to ensure that
// value lifetimes are not observably shortened.
if (bbi->isLexical() && !isNestedLexicalBeginBorrow(bbi)) {
return false;
}
auto kind = bbi->getOperand()->getOwnershipKind();
SmallVector<EndBorrowInst *, 16> endBorrows;
for (auto *op : bbi->getUses()) {
if (!op->isLifetimeEnding()) {
// Make sure that this operand can accept our arguments kind.
if (op->canAcceptKind(kind))
continue;
return false;
}
// Otherwise, this borrow is being consumed. See if our consuming inst is an
// end_borrow. If it isn't, then return false, this scope is
// needed. Otherwise, add the end_borrow to our list of end borrows.
auto *ebi = dyn_cast<EndBorrowInst>(op->getUser());
if (!ebi) {
return false;
}
endBorrows.push_back(ebi);
}
// At this point, we know that the begin_borrow's operand can be
// used as an argument to all non-end borrow uses. Eliminate the
// begin borrow and end borrows.
while (!endBorrows.empty()) {
auto *ebi = endBorrows.pop_back_val();
eraseInstruction(ebi);
}
eraseAndRAUWSingleValueInstruction(bbi, bbi->getOperand());
return true;
}
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