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111 lines
3.7 KiB
C++
111 lines
3.7 KiB
C++
//===--- BasicBlockBits.h - SILBasicBlock bit utilities ---------*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines utilities for BasicBlock bit fields and sets.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_SIL_BASICBLOCKBITS_H
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#define SWIFT_SIL_BASICBLOCKBITS_H
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#include "swift/SIL/SILBitfield.h"
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namespace swift {
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/// Utility to add a custom bitfield to a function's basic blocks.
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///
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/// This can be used by transforms to store temporary flags or tiny values per
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/// basic block.
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/// The bits are stored in a 32 bit field within each basic block (\see
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/// SILBasicBlock::customBits) which is very efficient: no memory allocation
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/// is needed, no hash set or map is needed for lookup and there is no
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/// initialization cost (in contrast to BasicBlockData which needs to iterate
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/// over all blocks at initialization).
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///
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/// Invariants:
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/// * BasicBlockBitfield instances must be allocated and deallocated
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/// following a strict stack discipline, because bit-positions in
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/// SILBasicBlock::customBits are "allocated" and "freed" with a stack-allocation
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/// algorithm. This means, it's fine to use a BasicBlockBitfield as (or in)
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/// local variables, e.g. in transformations. But it's not possible to store
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/// a BasicBlockBitfield in an Analysis.
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/// * The total number of bits which are alive at the same time must not exceed
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/// 32 (the size of SILBasicBlock::customBits).
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class BasicBlockBitfield : public SILBitfield<BasicBlockBitfield, SILBasicBlock> {
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template <class, class> friend class SILBitfield;
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BasicBlockBitfield *insertInto(SILFunction *function) {
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BasicBlockBitfield *oldParent = function->newestAliveBlockBitfield;
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function->newestAliveBlockBitfield = this;
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return oldParent;
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}
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public:
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BasicBlockBitfield(SILFunction *function, int size) :
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SILBitfield(function, size, insertInto(function)) {}
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~BasicBlockBitfield() {
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assert(function->newestAliveBlockBitfield == this &&
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"BasicBlockBitfield destructed too early");
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function->newestAliveBlockBitfield = parent;
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}
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};
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/// A BasicBlockBitfield containing a single bit - a flag.
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class BasicBlockFlag {
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BasicBlockBitfield bit;
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public:
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BasicBlockFlag(SILFunction *function) : bit(function, 1) {}
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SILFunction *getFunction() const { return bit.getFunction(); }
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bool get(SILBasicBlock *block) const { return (bool)bit.get(block); }
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void set(SILBasicBlock *block, bool value = true) {
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bit.set(block, (unsigned)value);
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}
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void reset(SILBasicBlock *block) { bit.set(block, 0); }
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/// Sets the flag and returns the old value.
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bool testAndSet(SILBasicBlock *block) {
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bool oldValue = get(block);
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set(block);
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return oldValue;
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}
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};
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/// A BasicBlockFlag with a set-like API.
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class BasicBlockSet {
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BasicBlockFlag flag;
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public:
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using Element = SILBasicBlock *;
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BasicBlockSet(SILFunction *function) : flag(function) {}
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SILFunction *getFunction() const { return flag.getFunction(); }
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bool contains(SILBasicBlock *block) const { return flag.get(block); }
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/// Returns true if \p block was not contained in the set before inserting.
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bool insert(SILBasicBlock *block) { return !flag.testAndSet(block); }
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void erase(SILBasicBlock *block) { flag.reset(block); }
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};
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using BasicBlockSetWithSize = KnownSizeSet<BasicBlockSet>;
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} // namespace swift
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#endif
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