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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef jit_ICState_h
#define jit_ICState_h
#include "jit/JitOptions.h"
namespace js {
namespace jit {
// Used to track trial inlining status for a Baseline IC.
// See also setTrialInliningState below.
enum class TrialInliningState : uint8_t {
Initial = 0,
Candidate,
Inlined,
MonomorphicInlined,
Failure,
};
// ICState stores information about a Baseline or Ion IC.
class ICState {
public:
// When we attach the maximum number of stubs, we discard all stubs and
// transition the IC to Megamorphic to attach stubs that are more generic
// (handle more cases). If we again attach the maximum number of stubs, we
// transition to Generic and (depending on the IC) will either attach a
// single stub that handles everything or stop attaching new stubs.
//
// We also transition to Generic when we repeatedly fail to attach a stub,
// to avoid wasting time trying.
enum class Mode : uint8_t { Specialized = 0, Megamorphic, Generic };
private:
uint8_t mode_ : 2;
// The TrialInliningState for a Baseline IC.
uint8_t trialInliningState_ : 3;
// Whether WarpOracle created a snapshot based on stubs attached to this
// Baseline IC.
bool usedByTranspiler_ : 1;
// Whether stubs attached to this IC have been folded together into a single
// stub. Used as a hint when attaching additional stubs to try folding them
// too. The folded stub may be removed later by GC sweeping so this is not
// exact.
bool mayHaveFoldedStub_ : 1;
// Number of optimized stubs currently attached to this IC.
uint8_t numOptimizedStubs_;
// Number of times we failed to attach a stub.
uint8_t numFailures_;
static const size_t MaxOptimizedStubs = 6;
void setMode(Mode mode) {
mode_ = uint32_t(mode);
MOZ_ASSERT(Mode(mode_) == mode, "mode must fit in bitfield");
}
void transition(Mode mode) {
MOZ_ASSERT(mode > this->mode());
setMode(mode);
numFailures_ = 0;
}
MOZ_ALWAYS_INLINE size_t maxFailures() const {
// Allow more failures if we attached stubs.
static_assert(MaxOptimizedStubs == 6,
"numFailures_/maxFailures should fit in uint8_t");
size_t res = 5 + size_t(40) * numOptimizedStubs_;
MOZ_ASSERT(res <= UINT8_MAX, "numFailures_ should not overflow");
return res;
}
public:
ICState() { reset(); }
Mode mode() const { return Mode(mode_); }
size_t numOptimizedStubs() const { return numOptimizedStubs_; }
bool hasFailures() const { return (numFailures_ != 0); }
bool newStubIsFirstStub() const {
return (mode() == Mode::Specialized && numOptimizedStubs() == 0);
}
MOZ_ALWAYS_INLINE bool canAttachStub() const {
// Note: we cannot assert that numOptimizedStubs_ <= MaxOptimizedStubs
// because old-style baseline ICs may attach more stubs than
// MaxOptimizedStubs allows.
if (mode() == Mode::Generic || JitOptions.disableCacheIR) {
return false;
}
return true;
}
[[nodiscard]] MOZ_ALWAYS_INLINE bool shouldTransition() {
// Note: we cannot assert that numOptimizedStubs_ <= MaxOptimizedStubs
// because old-style baseline ICs may attach more stubs than
// MaxOptimizedStubs allows.
if (mode() == Mode::Generic) {
return false;
}
if (numOptimizedStubs_ < MaxOptimizedStubs &&
numFailures_ < maxFailures()) {
return false;
}
return true;
}
// If this returns true, we transitioned to a new mode and the caller
// should discard all stubs.
[[nodiscard]] MOZ_ALWAYS_INLINE bool maybeTransition() {
if (!shouldTransition()) {
return false;
}
if (numFailures_ >= maxFailures() || mode() == Mode::Megamorphic) {
transition(Mode::Generic);
return true;
}
MOZ_ASSERT(mode() == Mode::Specialized);
transition(Mode::Megamorphic);
return true;
}
void reset() {
setMode(Mode::Specialized);
#ifdef DEBUG
if (JitOptions.forceMegamorphicICs) {
setMode(Mode::Megamorphic);
}
#endif
trialInliningState_ = uint32_t(TrialInliningState::Initial);
usedByTranspiler_ = false;
mayHaveFoldedStub_ = false;
numOptimizedStubs_ = 0;
numFailures_ = 0;
}
void trackAttached() {
// We'd like to assert numOptimizedStubs_ < MaxOptimizedStubs, but
// since this code is also used for non-CacheIR Baseline stubs, assert
// < 16 for now. Note that we do have the stronger assert in other
// methods, because they are only used by CacheIR ICs.
MOZ_ASSERT(numOptimizedStubs_ < 16);
numOptimizedStubs_++;
// As a heuristic, reduce the failure count after each successful attach
// to delay hitting Generic mode. Reset to 1 instead of 0 so that
// code which inspects state can distinguish no-failures from rare-failures.
numFailures_ = std::min(numFailures_, static_cast<uint8_t>(1));
}
void trackNotAttached() {
// Note: we can't assert numFailures_ < maxFailures() because
// maxFailures() depends on numOptimizedStubs_ and it's possible a
// GC discarded stubs before we got here.
numFailures_++;
MOZ_ASSERT(numFailures_ > 0, "numFailures_ should not overflow");
}
void trackUnlinkedStub() {
MOZ_ASSERT(numOptimizedStubs_ > 0);
numOptimizedStubs_--;
}
void trackUnlinkedAllStubs() { numOptimizedStubs_ = 0; }
void clearUsedByTranspiler() { usedByTranspiler_ = false; }
void setUsedByTranspiler() { usedByTranspiler_ = true; }
bool usedByTranspiler() const { return usedByTranspiler_; }
void clearMayHaveFoldedStub() { mayHaveFoldedStub_ = false; }
void setMayHaveFoldedStub() { mayHaveFoldedStub_ = true; }
bool mayHaveFoldedStub() const { return mayHaveFoldedStub_; }
TrialInliningState trialInliningState() const {
return TrialInliningState(trialInliningState_);
}
void setTrialInliningState(TrialInliningState state) {
#ifdef DEBUG
// Moving to the Failure state is always valid. The other states should
// happen in this order:
//
// Initial -> Candidate --> Inlined
// \-> MonomorphicInlined
//
// This ensures we perform trial inlining at most once per IC site.
if (state != TrialInliningState::Failure) {
switch (trialInliningState()) {
case TrialInliningState::Initial:
MOZ_ASSERT(state == TrialInliningState::Candidate);
break;
case TrialInliningState::Candidate:
MOZ_ASSERT(state == TrialInliningState::Candidate ||
state == TrialInliningState::Inlined ||
state == TrialInliningState::MonomorphicInlined);
break;
case TrialInliningState::Inlined:
case TrialInliningState::MonomorphicInlined:
case TrialInliningState::Failure:
MOZ_CRASH("Inlined and Failure can only change to Failure");
break;
}
}
#endif
trialInliningState_ = uint32_t(state);
MOZ_ASSERT(trialInliningState() == state,
"TrialInliningState must fit in bitfield");
}
};
} // namespace jit
} // namespace js
#endif /* jit_ICState_h */
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