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7203a4fa73
The old analysis pass doesn't take into account profile data, nor does it consider post-dominance. It primarily dealt with _fastPath/_slowPath. A block that is dominated by a cold block is itself cold. That's true whether it's forwards or backwards dominance. We can also consider a call to any `Never` returning function as a cold-exit, though the block(s) leading up to that call may be executed frequently because of concurrency. For now, I'm ignoring the concurrency case and assuming it's cold. To make use of this "no return" prediction, use the `-enable-noreturn-prediction` flag, which is currently off by default.
63 lines
1.9 KiB
C++
63 lines
1.9 KiB
C++
//===------------ ProfileCounter.h - PGO Propfile counter -------*- 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 - 2017 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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/// \file Declares ProfileCounter, a convenient type for PGO
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_BASIC_PROFILECOUNTER_H
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#define SWIFT_BASIC_PROFILECOUNTER_H
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#include <cassert>
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#include <cstdint>
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namespace swift {
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/// A class designed to be smaller than using Optional<uint64_t> for PGO
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class ProfileCounter {
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private:
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uint64_t count;
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public:
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explicit constexpr ProfileCounter() : count(UINT64_MAX) {}
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constexpr ProfileCounter(uint64_t Count) : count(Count) {
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if (Count == UINT64_MAX) {
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count = UINT64_MAX - 1;
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}
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}
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bool hasValue() const { return count != UINT64_MAX; }
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uint64_t getValue() const {
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assert(hasValue());
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return count;
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}
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explicit operator bool() const { return hasValue(); }
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/// Saturating addition of another counter to this one, meaning that overflow
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/// is avoided. If overflow would have happened, this function returns true
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/// and the maximum representable value will be set in this counter.
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bool add_saturating(ProfileCounter other) {
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assert(hasValue() && other.hasValue());
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// Will we go over the max representable value by adding other?
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if (count > ((UINT64_MAX-1) - other.count)) {
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count = UINT64_MAX - 1;
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return true;
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}
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count += other.count;
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return false;
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}
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};
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} // end namespace swift
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#endif // SWIFT_BASIC_PROFILECOUNTER_H
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