src/jit/CompileInfo.h

/* -*- 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_CompileInfo_h
#define jit_CompileInfo_h

#include "mozilla/Assertions.h"  // MOZ_ASSERT
#include "mozilla/Maybe.h"       // mozilla::Maybe, mozilla::Some

#include <algorithm>  // std::max
#include <stdint.h>   // uint32_t

#include "jit/CompileWrappers.h"  // CompileRuntime
#include "jit/JitFrames.h"        // MinJITStackSize
#include "js/TypeDecls.h"         // jsbytecode
#include "vm/BindingKind.h"       // BindingLocation
#include "vm/BytecodeUtil.h"      // JSOp
#include "vm/JSAtomState.h"       // JSAtomState
#include "vm/JSFunction.h"        // JSFunction
#include "vm/JSScript.h"          // JSScript
#include "vm/Scope.h"             // BindingIter

namespace js {

class ModuleObject;

namespace jit {

class InlineScriptTree;

inline unsigned StartArgSlot(JSScript* script) {
  // Reserved slots:
  // Slot 0: Environment chain.
  // Slot 1: Return value.

  // When needed:
  // Slot 2: Argumentsobject.

  // Note: when updating this, please also update the assert in
  // SnapshotWriter::startFrame
  return 2 + (script->needsArgsObj() ? 1 : 0);
}

inline unsigned CountArgSlots(JSScript* script, JSFunction* fun) {
  // Slot x + 0: This value.
  // Slot x + 1: Argument 1.
  // ...
  // Slot x + n: Argument n.

  // Note: when updating this, please also update the assert in
  // SnapshotWriter::startFrame
  return StartArgSlot(script) + (fun ? fun->nargs() + 1 : 0);
}

// Contains information about the compilation source for IR being generated.
class CompileInfo {
 public:
  CompileInfo(CompileRuntime* runtime, JSScript* script, JSFunction* fun,
              jsbytecode* osrPc, bool scriptNeedsArgsObj,
              InlineScriptTree* inlineScriptTree)
      : script_(script),
        fun_(fun),
        osrPc_(osrPc),
        scriptNeedsArgsObj_(scriptNeedsArgsObj),
        hadEagerTruncationBailout_(script->hadEagerTruncationBailout()),
        hadSpeculativePhiBailout_(script->hadSpeculativePhiBailout()),
        hadLICMInvalidation_(script->hadLICMInvalidation()),
        hadReorderingBailout_(script->hadReorderingBailout()),
        hadBoundsCheckBailout_(script->failedBoundsCheck()),
        hadUnboxFoldingBailout_(script->hadUnboxFoldingBailout()),
        mayReadFrameArgsDirectly_(script->mayReadFrameArgsDirectly()),
        anyFormalIsForwarded_(script->anyFormalIsForwarded()),
        isDerivedClassConstructor_(script->isDerivedClassConstructor()),
        inlineScriptTree_(inlineScriptTree) {
    MOZ_ASSERT_IF(osrPc, JSOp(*osrPc) == JSOp::LoopHead);

    // The function here can flow in from anywhere so look up the canonical
    // function to ensure that we do not try to embed a nursery pointer in
    // jit-code. Precisely because it can flow in from anywhere, it's not
    // guaranteed to be non-lazy. Hence, don't access its script!
    if (fun_) {
      fun_ = fun_->baseScript()->function();
      MOZ_ASSERT(fun_->isTenured());
    }

    nimplicit_ = StartArgSlot(script) /* env chain and argument obj */
                 + (fun ? 1 : 0);     /* this */
    nargs_ = fun ? fun->nargs() : 0;
    nlocals_ = script->nfixed();

    // An extra slot is needed for global scopes because InitGLexical (stack
    // depth 1) is compiled as a SetProp (stack depth 2) on the global lexical
    // scope.
    uint32_t extra = script->isGlobalCode() ? 1 : 0;
    nstack_ = std::max<unsigned>(script->nslots() - script->nfixed(),
                                 MinJITStackSize) +
              extra;
    nslots_ = nimplicit_ + nargs_ + nlocals_ + nstack_;

    // For derived class constructors, find and cache the frame slot for
    // the .this binding. This slot is assumed to be always
    // observable. See isObservableFrameSlot.
    if (script->isDerivedClassConstructor()) {
      MOZ_ASSERT(script->functionHasThisBinding());
      for (BindingIter bi(script); bi; bi++) {
        if (bi.name() != runtime->names().dotThis) {
          continue;
        }
        BindingLocation loc = bi.location();
        if (loc.kind() == BindingLocation::Kind::Frame) {
          thisSlotForDerivedClassConstructor_ =
              mozilla::Some(localSlot(loc.slot()));
          break;
        }
      }
    }

    // If the script uses an environment in body, the environment chain
    // will need to be observable.
    needsBodyEnvironmentObject_ = script->needsBodyEnvironment();
    funNeedsSomeEnvironmentObject_ =
        fun ? fun->needsSomeEnvironmentObject() : false;
  }

  explicit CompileInfo(unsigned nlocals)
      : script_(nullptr),
        fun_(nullptr),
        osrPc_(nullptr),
        scriptNeedsArgsObj_(false),
        hadEagerTruncationBailout_(false),
        hadSpeculativePhiBailout_(false),
        hadLICMInvalidation_(false),
        hadReorderingBailout_(false),
        hadBoundsCheckBailout_(false),
        hadUnboxFoldingBailout_(false),
        mayReadFrameArgsDirectly_(false),
        anyFormalIsForwarded_(false),
        inlineScriptTree_(nullptr),
        needsBodyEnvironmentObject_(false),
        funNeedsSomeEnvironmentObject_(false) {
    nimplicit_ = 0;
    nargs_ = 0;
    nlocals_ = nlocals;
    nstack_ = 1; /* For FunctionCompiler::pushPhiInput/popPhiOutput */
    nslots_ = nlocals_ + nstack_;
  }

  JSScript* script() const { return script_; }
  bool compilingWasm() const { return script() == nullptr; }
  JSFunction* funMaybeLazy() const { return fun_; }
  ModuleObject* module() const { return script_->module(); }
  jsbytecode* osrPc() const { return osrPc_; }
  InlineScriptTree* inlineScriptTree() const { return inlineScriptTree_; }

  const char* filename() const { return script_->filename(); }

  unsigned lineno() const { return script_->lineno(); }

  // Total number of slots: args, locals, and stack.
  unsigned nslots() const { return nslots_; }

  // Number of slots needed for env chain, return value,
  // maybe argumentsobject and this value.
  unsigned nimplicit() const { return nimplicit_; }
  // Number of arguments (without counting this value).
  unsigned nargs() const { return nargs_; }
  // Number of slots needed for all local variables.  This includes "fixed
  // vars" (see above) and also block-scoped locals.
  unsigned nlocals() const { return nlocals_; }
  unsigned ninvoke() const { return nslots_ - nstack_; }

  uint32_t environmentChainSlot() const {
    MOZ_ASSERT(script());
    return 0;
  }
  uint32_t returnValueSlot() const {
    MOZ_ASSERT(script());
    return 1;
  }
  uint32_t argsObjSlot() const {
    MOZ_ASSERT(needsArgsObj());
    return 2;
  }
  uint32_t thisSlot() const {
    MOZ_ASSERT(funMaybeLazy());
    MOZ_ASSERT(nimplicit_ > 0);
    return nimplicit_ - 1;
  }
  uint32_t firstArgSlot() const { return nimplicit_; }
  uint32_t argSlotUnchecked(uint32_t i) const {
    // During initialization, some routines need to get at arg
    // slots regardless of how regular argument access is done.
    MOZ_ASSERT(i < nargs_);
    return nimplicit_ + i;
  }
  uint32_t argSlot(uint32_t i) const {
    // This should only be accessed when compiling functions for
    // which argument accesses don't need to go through the
    // argument object.
    MOZ_ASSERT(!argsObjAliasesFormals());
    return argSlotUnchecked(i);
  }
  uint32_t firstLocalSlot() const { return nimplicit_ + nargs_; }
  uint32_t localSlot(uint32_t i) const { return firstLocalSlot() + i; }
  uint32_t firstStackSlot() const { return firstLocalSlot() + nlocals(); }
  uint32_t stackSlot(uint32_t i) const { return firstStackSlot() + i; }

  uint32_t totalSlots() const {
    MOZ_ASSERT(script() && funMaybeLazy());
    return nimplicit() + nargs() + nlocals();
  }

  bool hasMappedArgsObj() const { return script()->hasMappedArgsObj(); }
  bool needsArgsObj() const { return scriptNeedsArgsObj_; }
  bool argsObjAliasesFormals() const {
    return scriptNeedsArgsObj_ && script()->hasMappedArgsObj();
  }

  bool needsBodyEnvironmentObject() const {
    return needsBodyEnvironmentObject_;
  }

  enum class SlotObservableKind {
    // This slot must be preserved because it's observable outside SSA uses.
    // It can't be recovered before or during bailout.
    ObservableNotRecoverable,

    // This slot must be preserved because it's observable, but it can be
    // recovered.
    ObservableRecoverable,

    // This slot is not observable outside SSA uses.
    NotObservable,
  };

  inline SlotObservableKind getSlotObservableKind(uint32_t slot) const {
    // Locals and expression stack slots.
    if (slot >= firstLocalSlot()) {
      // The |this| slot for a derived class constructor is a local slot.
      // It should never be optimized out, as a Debugger might need to perform
      // TDZ checks on it via, e.g., an exceptionUnwind handler. The TDZ check
      // is required for correctness if the handler decides to continue
      // execution.
      if (thisSlotForDerivedClassConstructor_ &&
          *thisSlotForDerivedClassConstructor_ == slot) {
        return SlotObservableKind::ObservableNotRecoverable;
      }
      return SlotObservableKind::NotObservable;
    }

    // Formal argument slots.
    if (slot >= firstArgSlot()) {
      MOZ_ASSERT(funMaybeLazy());
      MOZ_ASSERT(slot - firstArgSlot() < nargs());

      // Preserve formal arguments if they might be read when creating a rest or
      // arguments object. In non-strict scripts, Function.arguments can create
      // an arguments object dynamically so we always preserve the arguments.
      if (mayReadFrameArgsDirectly_ || !script()->strict()) {
        return SlotObservableKind::ObservableRecoverable;
      }
      return SlotObservableKind::NotObservable;
    }

    // |this| slot is observable but it can be recovered.
    if (funMaybeLazy() && slot == thisSlot()) {
      return SlotObservableKind::ObservableRecoverable;
    }

    // Environment chain slot.
    if (slot == environmentChainSlot()) {
      // If environments can be added in the body (after the prologue) we need
      // to preserve the environment chain slot. It can't be recovered.
      if (needsBodyEnvironmentObject()) {
        return SlotObservableKind::ObservableNotRecoverable;
      }
      // If the function may need an arguments object, also preserve the
      // environment chain because it may be needed to reconstruct the arguments
      // object during bailout.
      if (funNeedsSomeEnvironmentObject_ || needsArgsObj()) {
        return SlotObservableKind::ObservableRecoverable;
      }
      return SlotObservableKind::NotObservable;
    }

    // The arguments object is observable. If it does not escape, it can
    // be recovered.
    if (needsArgsObj() && slot == argsObjSlot()) {
      MOZ_ASSERT(funMaybeLazy());
      return SlotObservableKind::ObservableRecoverable;
    }

    MOZ_ASSERT(slot == returnValueSlot());
    return SlotObservableKind::NotObservable;
  }

  // Returns true if a slot can be observed out-side the current frame while
  // the frame is active on the stack.  This implies that these definitions
  // would have to be executed and that they cannot be removed even if they
  // are unused.
  inline bool isObservableSlot(uint32_t slot) const {
    SlotObservableKind kind = getSlotObservableKind(slot);
    return (kind == SlotObservableKind::ObservableNotRecoverable ||
            kind == SlotObservableKind::ObservableRecoverable);
  }

  // Returns true if a slot can be recovered before or during a bailout.  A
  // definition which can be observed and recovered, implies that this
  // definition can be optimized away as long as we can compute its values.
  bool isRecoverableOperand(uint32_t slot) const {
    SlotObservableKind kind = getSlotObservableKind(slot);
    return (kind == SlotObservableKind::ObservableRecoverable ||
            kind == SlotObservableKind::NotObservable);
  }

  // Check previous bailout states to prevent doing the same bailout in the
  // next compilation.
  bool hadEagerTruncationBailout() const { return hadEagerTruncationBailout_; }
  bool hadSpeculativePhiBailout() const { return hadSpeculativePhiBailout_; }
  bool hadLICMInvalidation() const { return hadLICMInvalidation_; }
  bool hadReorderingBailout() const { return hadReorderingBailout_; }
  bool hadBoundsCheckBailout() const { return hadBoundsCheckBailout_; }
  bool hadUnboxFoldingBailout() const { return hadUnboxFoldingBailout_; }

  bool mayReadFrameArgsDirectly() const { return mayReadFrameArgsDirectly_; }
  bool anyFormalIsForwarded() const { return anyFormalIsForwarded_; }

  bool isDerivedClassConstructor() const { return isDerivedClassConstructor_; }

 private:
  unsigned nimplicit_;
  unsigned nargs_;
  unsigned nlocals_;
  unsigned nstack_;
  unsigned nslots_;
  mozilla::Maybe<unsigned> thisSlotForDerivedClassConstructor_;
  JSScript* script_;
  JSFunction* fun_;
  jsbytecode* osrPc_;

  bool scriptNeedsArgsObj_;

  // Record the state of previous bailouts in order to prevent compiling the
  // same function identically the next time.
  bool hadEagerTruncationBailout_;
  bool hadSpeculativePhiBailout_;
  bool hadLICMInvalidation_;
  bool hadReorderingBailout_;
  bool hadBoundsCheckBailout_;
  bool hadUnboxFoldingBailout_;

  bool mayReadFrameArgsDirectly_;
  bool anyFormalIsForwarded_;

  bool isDerivedClassConstructor_;

  InlineScriptTree* inlineScriptTree_;

  // Whether a script needs environments within its body. This informs us
  // that the environment chain is not easy to reconstruct.
  bool needsBodyEnvironmentObject_;
  bool funNeedsSomeEnvironmentObject_;
};

}  // namespace jit
}  // namespace js

#endif /* jit_CompileInfo_h */