Source/JavaScriptCore/b3/B3StackmapValue.h - WebKit - Git at Google

 /*
  * Copyright (C) 2015-2018 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #pragma once

 #if ENABLE(B3_JIT)

 #include "B3ConstrainedValue.h"
 #include "B3Value.h"
 #include "B3ValueRep.h"
 #include "CCallHelpers.h"
 #include "RegisterSet.h"
 #include <wtf/SharedTask.h>

 namespace JSC { namespace B3 {

 class StackmapGenerationParams;

 typedef void StackmapGeneratorFunction(CCallHelpers&, const StackmapGenerationParams&);
 typedef SharedTask<StackmapGeneratorFunction> StackmapGenerator;

 class JS_EXPORT_PRIVATE StackmapValue : public Value {
 public:
     static bool accepts(Kind kind)
     {
         // This needs to include opcodes of all subclasses.
         switch (kind.opcode()) {
         case CheckAdd:
         case CheckSub:
         case CheckMul:
         case Check:
         case Patchpoint:
             return true;
         default:
             return false;
         }
     }

     ~StackmapValue();

     // Use this to add children.
     void append(const ConstrainedValue& value)
     {
         append(value.value(), value.rep());
     }

     void append(Value*, const ValueRep&);

     template<typename VectorType>
     void appendVector(const VectorType& vector)
     {
         for (const auto& value : vector)
             append(value);
     }

     // Helper for appending a bunch of values with some ValueRep.
     template<typename VectorType>
     void appendVectorWithRep(const VectorType& vector, const ValueRep& rep)
     {
         for (Value* value : vector)
             append(value, rep);
     }

     // Helper for appending cold any's. This often used by clients to implement OSR.
     template<typename VectorType>
     void appendColdAnys(const VectorType& vector)
     {
         appendVectorWithRep(vector, ValueRep::ColdAny);
     }
     template<typename VectorType>
     void appendLateColdAnys(const VectorType& vector)
     {
         appendVectorWithRep(vector, ValueRep::LateColdAny);
     }

     // This is a helper for something you might do a lot of: append a value that should be constrained
     // to SomeRegister.
     void appendSomeRegister(Value*);
     void appendSomeRegisterWithClobber(Value*);

     const Vector<ValueRep>& reps() const { return m_reps; }

     // Stackmaps allow you to specify that the operation may clobber some registers. Clobbering a register
     // means that the operation appears to store a value into the register, but the compiler doesn't
     // assume to know anything about what kind of value might have been stored. In B3's model of
     // execution, registers are read or written at instruction boundaries rather than inside the
     // instructions themselves. A register could be read or written immediately before the instruction
     // executes, or immediately after. Note that at a boundary between instruction A and instruction B we
     // simultaneously look at what A does after it executes and what B does before it executes. This is
     // because when the compiler considers what happens to registers, it views the boundary between two
     // instructions as a kind of atomic point where the late effects of A happen at the same time as the
     // early effects of B.
     //
     // The compiler views a stackmap as a single instruction, even though of course the stackmap may be
     // composed of any number of instructions (if it's a Patchpoint). You can claim that a stackmap value
     // clobbers a set of registers before the stackmap's instruction or after. Clobbering before is called
     // early clobber, while clobbering after is called late clobber.
     //
     // This is quite flexible but it has its limitations. Any register listed as an early clobber will
     // interfere with all uses of the stackmap. Any register listed as a late clobber will interfere with
     // all defs of the stackmap (i.e. the result). This means that it's currently not possible to claim
     // to clobber a register while still allowing that register to be used for both an input and an output
     // of the instruction. It just so happens that B3's sole client (the FTL) currently never wants to
     // convey such a constraint, but it will want it eventually (FIXME:
     // https://bugs.webkit.org/show_bug.cgi?id=151823).
     //
     // Note that a common use case of early clobber sets is to indicate that this is the set of registers
     // that shall not be used for inputs to the value. But B3 supports two different ways of specifying
     // this, the other being LateUse in combination with late clobber (not yet available to stackmaps
     // directly, FIXME: https://bugs.webkit.org/show_bug.cgi?id=151335). A late use makes the use of that
     // value appear to happen after the instruction. This means that a late use cannot use the same
     // register as the result and it cannot use the same register as either early or late clobbered
     // registers. Late uses are usually a better way of saying that a clobbered register cannot be used
     // for an input. Early clobber means that some register(s) interfere with *all* inputs, while LateUse
     // means that some value interferes with whatever is live after the instruction. Below is a list of
     // examples of how the FTL can handle its various kinds of scenarios using a combination of early
     // clobber, late clobber, and late use. These examples are for X86_64, w.l.o.g.
     //
     // Basic ById patchpoint: Early and late clobber of r11. Early clobber prevents any inputs from using
     // r11 since that would mess with the MacroAssembler's assumptions when we
     // AllowMacroScratchRegisterUsage. Late clobber tells B3 that the patchpoint may overwrite r11.
     //
     // ById patchpoint in a try block with some live state: This might throw an exception after already
     // assigning to the result. So, this should LateUse all stackmap values to ensure that the stackmap
     // values don't interfere with the result. Note that we do not LateUse the non-OSR inputs of the ById
     // since LateUse implies that the use is cold: the register allocator will assume that the use is not
     // important for the critical path. Also, early and late clobber of r11.
     //
     // Basic ByIdFlush patchpoint: We could do Flush the same way we did it with LLVM: ignore it and let
     // PolymorphicAccess figure it out. Or, we could add internal clobber support (FIXME:
     // https://bugs.webkit.org/show_bug.cgi?id=151823). Or, we could do it by early clobbering r11, late
     // clobbering all volatile registers, and constraining the result to some register. Or, we could do
     // that but leave the result constrained to SomeRegister, which will cause it to use a callee-save
     // register. Internal clobber support would allow us to use SomeRegister while getting the result into
     // a volatile register.
     //
     // ByIdFlush patchpoint in a try block with some live state: LateUse all for-OSR stackmap values,
     // early clobber of r11 to prevent the other inputs from using r11, and late clobber of all volatile
     // registers to make way for the call. To handle the result, we could do any of what is listed in the
     // previous paragraph.
     //
     // Basic JS call: Force all non-OSR inputs into specific locations (register, stack, whatever).
     // All volatile registers are late-clobbered. The output is constrained to a register as well.
     //
     // JS call in a try block with some live state: LateUse all for-OSR stackmap values, fully constrain
     // all non-OSR inputs and the result, and late clobber all volatile registers.
     //
     // JS tail call: Pass all inputs as a warm variant of Any (FIXME:
     // https://bugs.webkit.org/show_bug.cgi?id=151811).
     //
     // Note that we cannot yet do all of these things because although Air already supports all of these
     // various forms of uses (LateUse and warm unconstrained use), B3 doesn't yet expose all of it. The
     // bugs are:
     // https://bugs.webkit.org/show_bug.cgi?id=151335 (LateUse)
     // https://bugs.webkit.org/show_bug.cgi?id=151811 (warm Any)
     void clobberEarly(const RegisterSet& set)
     {
         m_earlyClobbered.merge(set);
     }

     void clobberLate(const RegisterSet& set)
     {
         m_lateClobbered.merge(set);
     }

     void clobber(const RegisterSet& set)
     {
         clobberEarly(set);
         clobberLate(set);
     }

     RegisterSet& earlyClobbered() { return m_earlyClobbered; }
     RegisterSet& lateClobbered() { return m_lateClobbered; }
     const RegisterSet& earlyClobbered() const { return m_earlyClobbered; }
     const RegisterSet& lateClobbered() const { return m_lateClobbered; }

     void setGenerator(RefPtr<StackmapGenerator> generator)
     {
         m_generator = generator;
     }

     template<typename Functor>
     void setGenerator(const Functor& functor)
     {
         m_generator = createSharedTask<StackmapGeneratorFunction>(functor);
     }

     RefPtr<StackmapGenerator> generator() const { return m_generator; }

     ConstrainedValue constrainedChild(unsigned index) const
     {
         return ConstrainedValue(child(index), index < m_reps.size() ? m_reps[index] : ValueRep::ColdAny);
     }

     void setConstrainedChild(unsigned index, const ConstrainedValue&);

     void setConstraint(unsigned index, const ValueRep&);

     class ConstrainedValueCollection {
     public:

         ConstrainedValueCollection(const StackmapValue& value)
             : m_value(value)
         {
         }

         unsigned size() const { return m_value.numChildren(); }

         ConstrainedValue at(unsigned index) const { return m_value.constrainedChild(index); }

         ConstrainedValue operator[](unsigned index) const { return at(index); }

         class iterator {
         public:
             using iterator_category = std::forward_iterator_tag;
             using value_type = ConstrainedValue;
             using difference_type = int;
             using pointer = void;
             using reference = ConstrainedValue;

             iterator()
                 : m_collection(nullptr)
                 , m_index(0)
             {
             }

             iterator(const ConstrainedValueCollection& collection, unsigned index)
                 : m_collection(&collection)
                 , m_index(index)
             {
             }

             ConstrainedValue operator*() const
             {
                 return m_collection->at(m_index);
             }

             iterator& operator++()
             {
                 m_index++;
                 return *this;
             }

             bool operator==(const iterator& other) const
             {
                 ASSERT(m_collection == other.m_collection);
                 return m_index == other.m_index;
             }

             bool operator!=(const iterator& other) const
             {
                 return !(*this == other);
             }

         private:
             const ConstrainedValueCollection* m_collection;
             unsigned m_index;
         };

         iterator begin() const { return iterator(*this, 0); }
         iterator end() const { return iterator(*this, size()); }

     private:
         const StackmapValue& m_value;
     };

     ConstrainedValueCollection constrainedChildren() const
     {
         return ConstrainedValueCollection(*this);
     }

     B3_SPECIALIZE_VALUE_FOR_VARARGS_CHILDREN

 protected:
     void dumpChildren(CommaPrinter&, PrintStream&) const override;
     void dumpMeta(CommaPrinter&, PrintStream&) const override;

     StackmapValue(CheckedOpcodeTag, Kind, Type, Origin);

 private:
     friend class CheckSpecial;
     friend class PatchpointSpecial;
     friend class StackmapGenerationParams;
     friend class StackmapSpecial;

     Vector<ValueRep> m_reps;
     RefPtr<StackmapGenerator> m_generator;
     RegisterSet m_earlyClobbered;
     RegisterSet m_lateClobbered;
     RegisterSet m_usedRegisters; // Stackmaps could be further duplicated by Air, but that's unlikely, so we just merge the used registers sets if that were to happen.
 };

 } } // namespace JSC::B3

 #endif // ENABLE(B3_JIT)
	/*
	* Copyright (C) 2015-2018 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#pragma once

	#if ENABLE(B3_JIT)

	#include "B3ConstrainedValue.h"
	#include "B3Value.h"
	#include "B3ValueRep.h"
	#include "CCallHelpers.h"
	#include "RegisterSet.h"
	#include <wtf/SharedTask.h>

	namespace JSC { namespace B3 {

	class StackmapGenerationParams;

	typedef void StackmapGeneratorFunction(CCallHelpers&, const StackmapGenerationParams&);
	typedef SharedTask<StackmapGeneratorFunction> StackmapGenerator;

	class JS_EXPORT_PRIVATE StackmapValue : public Value {
	public:
	static bool accepts(Kind kind)
	{
	// This needs to include opcodes of all subclasses.
	switch (kind.opcode()) {
	case CheckAdd:
	case CheckSub:
	case CheckMul:
	case Check:
	case Patchpoint:
	return true;
	default:
	return false;
	}
	}

	~StackmapValue();

	// Use this to add children.
	void append(const ConstrainedValue& value)
	{
	append(value.value(), value.rep());
	}

	void append(Value*, const ValueRep&);

	template<typename VectorType>
	void appendVector(const VectorType& vector)
	{
	for (const auto& value : vector)
	append(value);
	}

	// Helper for appending a bunch of values with some ValueRep.
	template<typename VectorType>
	void appendVectorWithRep(const VectorType& vector, const ValueRep& rep)
	{
	for (Value* value : vector)
	append(value, rep);
	}

	// Helper for appending cold any's. This often used by clients to implement OSR.
	template<typename VectorType>
	void appendColdAnys(const VectorType& vector)
	{
	appendVectorWithRep(vector, ValueRep::ColdAny);
	}
	template<typename VectorType>
	void appendLateColdAnys(const VectorType& vector)
	{
	appendVectorWithRep(vector, ValueRep::LateColdAny);
	}

	// This is a helper for something you might do a lot of: append a value that should be constrained
	// to SomeRegister.
	void appendSomeRegister(Value*);
	void appendSomeRegisterWithClobber(Value*);

	const Vector<ValueRep>& reps() const { return m_reps; }

	// Stackmaps allow you to specify that the operation may clobber some registers. Clobbering a register
	// means that the operation appears to store a value into the register, but the compiler doesn't
	// assume to know anything about what kind of value might have been stored. In B3's model of
	// execution, registers are read or written at instruction boundaries rather than inside the
	// instructions themselves. A register could be read or written immediately before the instruction
	// executes, or immediately after. Note that at a boundary between instruction A and instruction B we
	// simultaneously look at what A does after it executes and what B does before it executes. This is
	// because when the compiler considers what happens to registers, it views the boundary between two
	// instructions as a kind of atomic point where the late effects of A happen at the same time as the
	// early effects of B.
	//
	// The compiler views a stackmap as a single instruction, even though of course the stackmap may be
	// composed of any number of instructions (if it's a Patchpoint). You can claim that a stackmap value
	// clobbers a set of registers before the stackmap's instruction or after. Clobbering before is called
	// early clobber, while clobbering after is called late clobber.
	//
	// This is quite flexible but it has its limitations. Any register listed as an early clobber will
	// interfere with all uses of the stackmap. Any register listed as a late clobber will interfere with
	// all defs of the stackmap (i.e. the result). This means that it's currently not possible to claim
	// to clobber a register while still allowing that register to be used for both an input and an output
	// of the instruction. It just so happens that B3's sole client (the FTL) currently never wants to
	// convey such a constraint, but it will want it eventually (FIXME:
	// https://bugs.webkit.org/show_bug.cgi?id=151823).
	//
	// Note that a common use case of early clobber sets is to indicate that this is the set of registers
	// that shall not be used for inputs to the value. But B3 supports two different ways of specifying
	// this, the other being LateUse in combination with late clobber (not yet available to stackmaps
	// directly, FIXME: https://bugs.webkit.org/show_bug.cgi?id=151335). A late use makes the use of that
	// value appear to happen after the instruction. This means that a late use cannot use the same
	// register as the result and it cannot use the same register as either early or late clobbered
	// registers. Late uses are usually a better way of saying that a clobbered register cannot be used
	// for an input. Early clobber means that some register(s) interfere with all inputs, while LateUse
	// means that some value interferes with whatever is live after the instruction. Below is a list of
	// examples of how the FTL can handle its various kinds of scenarios using a combination of early
	// clobber, late clobber, and late use. These examples are for X86_64, w.l.o.g.
	//
	// Basic ById patchpoint: Early and late clobber of r11. Early clobber prevents any inputs from using
	// r11 since that would mess with the MacroAssembler's assumptions when we
	// AllowMacroScratchRegisterUsage. Late clobber tells B3 that the patchpoint may overwrite r11.
	//
	// ById patchpoint in a try block with some live state: This might throw an exception after already
	// assigning to the result. So, this should LateUse all stackmap values to ensure that the stackmap
	// values don't interfere with the result. Note that we do not LateUse the non-OSR inputs of the ById
	// since LateUse implies that the use is cold: the register allocator will assume that the use is not
	// important for the critical path. Also, early and late clobber of r11.
	//
	// Basic ByIdFlush patchpoint: We could do Flush the same way we did it with LLVM: ignore it and let
	// PolymorphicAccess figure it out. Or, we could add internal clobber support (FIXME:
	// https://bugs.webkit.org/show_bug.cgi?id=151823). Or, we could do it by early clobbering r11, late
	// clobbering all volatile registers, and constraining the result to some register. Or, we could do
	// that but leave the result constrained to SomeRegister, which will cause it to use a callee-save
	// register. Internal clobber support would allow us to use SomeRegister while getting the result into
	// a volatile register.
	//
	// ByIdFlush patchpoint in a try block with some live state: LateUse all for-OSR stackmap values,
	// early clobber of r11 to prevent the other inputs from using r11, and late clobber of all volatile
	// registers to make way for the call. To handle the result, we could do any of what is listed in the
	// previous paragraph.
	//
	// Basic JS call: Force all non-OSR inputs into specific locations (register, stack, whatever).
	// All volatile registers are late-clobbered. The output is constrained to a register as well.
	//
	// JS call in a try block with some live state: LateUse all for-OSR stackmap values, fully constrain
	// all non-OSR inputs and the result, and late clobber all volatile registers.
	//
	// JS tail call: Pass all inputs as a warm variant of Any (FIXME:
	// https://bugs.webkit.org/show_bug.cgi?id=151811).
	//
	// Note that we cannot yet do all of these things because although Air already supports all of these
	// various forms of uses (LateUse and warm unconstrained use), B3 doesn't yet expose all of it. The
	// bugs are:
	// https://bugs.webkit.org/show_bug.cgi?id=151335 (LateUse)
	// https://bugs.webkit.org/show_bug.cgi?id=151811 (warm Any)
	void clobberEarly(const RegisterSet& set)
	{
	m_earlyClobbered.merge(set);
	}

	void clobberLate(const RegisterSet& set)
	{
	m_lateClobbered.merge(set);
	}

	void clobber(const RegisterSet& set)
	{
	clobberEarly(set);
	clobberLate(set);
	}

	RegisterSet& earlyClobbered() { return m_earlyClobbered; }
	RegisterSet& lateClobbered() { return m_lateClobbered; }
	const RegisterSet& earlyClobbered() const { return m_earlyClobbered; }
	const RegisterSet& lateClobbered() const { return m_lateClobbered; }

	void setGenerator(RefPtr<StackmapGenerator> generator)
	{
	m_generator = generator;
	}

	template<typename Functor>
	void setGenerator(const Functor& functor)
	{
	m_generator = createSharedTask<StackmapGeneratorFunction>(functor);
	}

	RefPtr<StackmapGenerator> generator() const { return m_generator; }

	ConstrainedValue constrainedChild(unsigned index) const
	{
	return ConstrainedValue(child(index), index < m_reps.size() ? m_reps[index] : ValueRep::ColdAny);
	}

	void setConstrainedChild(unsigned index, const ConstrainedValue&);

	void setConstraint(unsigned index, const ValueRep&);

	class ConstrainedValueCollection {
	public:

	ConstrainedValueCollection(const StackmapValue& value)
	: m_value(value)
	{
	}

	unsigned size() const { return m_value.numChildren(); }

	ConstrainedValue at(unsigned index) const { return m_value.constrainedChild(index); }

	ConstrainedValue operator[](unsigned index) const { return at(index); }

	class iterator {
	public:
	using iterator_category = std::forward_iterator_tag;
	using value_type = ConstrainedValue;
	using difference_type = int;
	using pointer = void;
	using reference = ConstrainedValue;

	iterator()
	: m_collection(nullptr)
	, m_index(0)
	{
	}

	iterator(const ConstrainedValueCollection& collection, unsigned index)
	: m_collection(&collection)
	, m_index(index)
	{
	}

	ConstrainedValue operator*() const
	{
	return m_collection->at(m_index);
	}

	iterator& operator++()
	{
	m_index++;
	return *this;
	}

	bool operator==(const iterator& other) const
	{
	ASSERT(m_collection == other.m_collection);
	return m_index == other.m_index;
	}

	bool operator!=(const iterator& other) const
	{
	return !(*this == other);
	}

	private:
	const ConstrainedValueCollection* m_collection;
	unsigned m_index;
	};

	iterator begin() const { return iterator(*this, 0); }
	iterator end() const { return iterator(*this, size()); }

	private:
	const StackmapValue& m_value;
	};

	ConstrainedValueCollection constrainedChildren() const
	{
	return ConstrainedValueCollection(*this);
	}

	B3_SPECIALIZE_VALUE_FOR_VARARGS_CHILDREN

	protected:
	void dumpChildren(CommaPrinter&, PrintStream&) const override;
	void dumpMeta(CommaPrinter&, PrintStream&) const override;

	StackmapValue(CheckedOpcodeTag, Kind, Type, Origin);

	private:
	friend class CheckSpecial;
	friend class PatchpointSpecial;
	friend class StackmapGenerationParams;
	friend class StackmapSpecial;

	Vector<ValueRep> m_reps;
	RefPtr<StackmapGenerator> m_generator;
	RegisterSet m_earlyClobbered;
	RegisterSet m_lateClobbered;
	RegisterSet m_usedRegisters; // Stackmaps could be further duplicated by Air, but that's unlikely, so we just merge the used registers sets if that were to happen.
	};

	} } // namespace JSC::B3

	#endif // ENABLE(B3_JIT)