Source/JavaScriptCore/b3/air/AirFixObviousSpills.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2016-2017 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.
  */

 #include "config.h"
 #include "AirFixObviousSpills.h"

 #if ENABLE(B3_JIT)

 #include "AirArgInlines.h"
 #include "AirCode.h"
 #include "AirInstInlines.h"
 #include "AirPhaseScope.h"
 #include <wtf/IndexMap.h>
 #include <wtf/ListDump.h>

 namespace JSC { namespace B3 { namespace Air {

 namespace {

 namespace AirFixObviousSpillsInternal {
 static const bool verbose = false;
 }

 class FixObviousSpills {
 public:
     FixObviousSpills(Code& code)
         : m_code(code)
         , m_atHead(code.size())
     {
     }

     void run()
     {
         if (AirFixObviousSpillsInternal::verbose)
             dataLog("Code before fixObviousSpills:\n", m_code);

         computeAliases();
         fixCode();
     }

 private:
     void computeAliases()
     {
         m_atHead[m_code[0]].wasVisited = true;

         bool changed = true;
         while (changed) {
             changed = false;

             for (BasicBlock* block : m_code) {
                 m_block = block;
                 m_state = m_atHead[block];
                 if (!m_state.wasVisited)
                     continue;

                 if (AirFixObviousSpillsInternal::verbose)
                     dataLog("Executing block ", *m_block, ": ", m_state, "\n");

                 for (m_instIndex = 0; m_instIndex < block->size(); ++m_instIndex)
                     executeInst();

                 for (BasicBlock* successor : block->successorBlocks()) {
                     State& toState = m_atHead[successor];
                     if (toState.wasVisited)
                         changed |= toState.merge(m_state);
                     else {
                         toState = m_state;
                         changed = true;
                     }
                 }
             }
         }
     }

     void fixCode()
     {
         for (BasicBlock* block : m_code) {
             m_block = block;
             m_state = m_atHead[block];
             RELEASE_ASSERT(m_state.wasVisited);

             for (m_instIndex = 0; m_instIndex < block->size(); ++m_instIndex) {
                 fixInst();
                 executeInst();
             }
         }
     }

     template<typename Func>
     void forAllAliases(const Func& func)
     {
         Inst& inst = m_block->at(m_instIndex);

         switch (inst.kind.opcode) {
         case Move:
             if (inst.args[0].isSomeImm()) {
                 if (inst.args[1].isReg())
                     func(RegConst(inst.args[1].reg(), inst.args[0].value()));
                 else if (isSpillSlot(inst.args[1]))
                     func(SlotConst(inst.args[1].stackSlot(), inst.args[0].value()));
             } else if (isSpillSlot(inst.args[0]) && inst.args[1].isReg()) {
                 if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
                     func(RegConst(inst.args[1].reg(), *constant));
                 func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::AllBits));
             } else if (inst.args[0].isReg() && isSpillSlot(inst.args[1])) {
                 if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
                     func(SlotConst(inst.args[1].stackSlot(), *constant));
                 func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::AllBits));
             }
             break;

         case Move32:
             if (inst.args[0].isSomeImm()) {
                 if (inst.args[1].isReg())
                     func(RegConst(inst.args[1].reg(), static_cast<uint32_t>(inst.args[0].value())));
                 else if (isSpillSlot(inst.args[1]))
                     func(SlotConst(inst.args[1].stackSlot(), static_cast<uint32_t>(inst.args[0].value())));
             } else if (isSpillSlot(inst.args[0]) && inst.args[1].isReg()) {
                 if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
                     func(RegConst(inst.args[1].reg(), static_cast<uint32_t>(*constant)));
                 func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::ZExt32));
             } else if (inst.args[0].isReg() && isSpillSlot(inst.args[1])) {
                 if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
                     func(SlotConst(inst.args[1].stackSlot(), static_cast<int32_t>(*constant)));
                 func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::Match32));
             }
             break;

         case MoveFloat:
             if (isSpillSlot(inst.args[0]) && inst.args[1].isReg())
                 func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::Match32));
             else if (inst.args[0].isReg() && isSpillSlot(inst.args[1]))
                 func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::Match32));
             break;

         case MoveDouble:
             if (isSpillSlot(inst.args[0]) && inst.args[1].isReg())
                 func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::AllBits));
             else if (inst.args[0].isReg() && isSpillSlot(inst.args[1]))
                 func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::AllBits));
             break;

         default:
             break;
         }
     }

     void executeInst()
     {
         Inst& inst = m_block->at(m_instIndex);

         if (AirFixObviousSpillsInternal::verbose)
             dataLog("    Executing ", inst, ": ", m_state, "\n");

         Inst::forEachDefWithExtraClobberedRegs<Arg>(
             &inst, &inst,
             [&] (const Arg& arg, Arg::Role, Bank, Width) {
                 if (AirFixObviousSpillsInternal::verbose)
                     dataLog("        Clobbering ", arg, "\n");
                 m_state.clobber(arg);
             });

         forAllAliases(
             [&] (const auto& alias) {
                 m_state.addAlias(alias);
             });
     }

     void fixInst()
     {
         Inst& inst = m_block->at(m_instIndex);

         if (AirFixObviousSpillsInternal::verbose)
             dataLog("Fixing inst ", inst, ": ", m_state, "\n");

         // Check if alias analysis says that this is unnecessary.
         bool shouldLive = true;
         forAllAliases(
             [&] (const auto& alias) {
                 shouldLive &= !m_state.contains(alias);
             });
         if (!shouldLive) {
             inst = Inst();
             return;
         }

         // First handle some special instructions.
         switch (inst.kind.opcode) {
         case Move: {
             if (inst.args[0].isBigImm() && inst.args[1].isReg()
                 && isValidForm(Add64, Arg::Imm, Arg::Tmp, Arg::Tmp)) {
                 // BigImm materializations are super expensive on both x86 and ARM. Let's try to
                 // materialize this bad boy using math instead. Note that we use unsigned math here
                 // since it's more deterministic.
                 uint64_t myValue = inst.args[0].value();
                 Reg myDest = inst.args[1].reg();
                 for (const RegConst& regConst : m_state.regConst) {
                     uint64_t otherValue = regConst.constant;

                     // Let's try add. That's the only thing that works on all platforms, since it's
                     // the only cheap arithmetic op that x86 does in three operands. Long term, we
                     // should add fancier materializations here for ARM if the BigImm is yuge.
                     uint64_t delta = myValue - otherValue;

                     if (Arg::isValidImmForm(delta)) {
                         inst.kind = Add64;
                         inst.args.resize(3);
                         inst.args[0] = Arg::imm(delta);
                         inst.args[1] = Tmp(regConst.reg);
                         inst.args[2] = Tmp(myDest);
                         return;
                     }
                 }
                 return;
             }
             break;
         }

         default:
             break;
         }

         // FIXME: This code should be taught how to simplify the spill-to-spill move
         // instruction. Basically it needs to know to remove the scratch arg.
         // https://bugs.webkit.org/show_bug.cgi?id=171133

         // Create a copy in case we invalidate the instruction. That doesn't happen often.
         Inst instCopy = inst;

         // The goal is to replace references to stack slots. We only care about early uses. We can't
         // handle UseDefs. We could teach this to handle UseDefs if we inserted a store instruction
         // after and we proved that the register aliased to the stack slot dies here. We can get that
         // information from the liveness analysis. We also can't handle late uses, because we don't
         // look at late clobbers when doing this.
         bool didThings = false;
         auto handleArg = [&] (Arg& arg, Arg::Role role, Bank, Width width) {
             if (!isSpillSlot(arg))
                 return;
             if (!Arg::isEarlyUse(role))
                 return;
             if (Arg::isAnyDef(role))
                 return;

             // Try to get a register if at all possible.
             if (const RegSlot* alias = m_state.getRegSlot(arg.stackSlot())) {
                 switch (width) {
                 case Width64:
                     if (alias->mode != RegSlot::AllBits)
                         return;
                     if (AirFixObviousSpillsInternal::verbose)
                         dataLog("    Replacing ", arg, " with ", alias->reg, "\n");
                     arg = Tmp(alias->reg);
                     didThings = true;
                     return;
                 case Width32:
                     if (AirFixObviousSpillsInternal::verbose)
                         dataLog("    Replacing ", arg, " with ", alias->reg, " (subwidth case)\n");
                     arg = Tmp(alias->reg);
                     didThings = true;
                     return;
                 default:
                     return;
                 }
             }

             // Revert to immediate if that didn't work.
             if (const SlotConst* alias = m_state.getSlotConst(arg.stackSlot())) {
                 if (AirFixObviousSpillsInternal::verbose)
                     dataLog("    Replacing ", arg, " with constant ", alias->constant, "\n");
                 if (Arg::isValidImmForm(alias->constant))
                     arg = Arg::imm(alias->constant);
                 else
                     arg = Arg::bigImm(alias->constant);
                 didThings = true;
                 return;
             }
         };

         inst.forEachArg(handleArg);
         if (!didThings || inst.isValidForm())
             return;

         // We introduced something invalid along the way. Back up and carefully handle each argument.
         inst = instCopy;
         ASSERT(inst.isValidForm());
         inst.forEachArg(
             [&] (Arg& arg, Arg::Role role, Bank bank, Width width) {
                 Arg argCopy = arg;
                 handleArg(arg, role, bank, width);
                 if (!inst.isValidForm())
                     arg = argCopy;
             });
     }

     static bool isSpillSlot(const Arg& arg)
     {
         return arg.isStack() && arg.stackSlot()->isSpill();
     }

     struct RegConst {
         RegConst()
         {
         }

         RegConst(Reg reg, int64_t constant)
             : reg(reg)
             , constant(constant)
         {
         }

         explicit operator bool() const
         {
             return !!reg;
         }

         bool operator==(const RegConst& other) const
         {
             return reg == other.reg
                 && constant == other.constant;
         }

         void dump(PrintStream& out) const
         {
             out.print(reg, "->", constant);
         }

         Reg reg;
         int64_t constant { 0 };
     };

     struct RegSlot {
         enum Mode : int8_t {
             AllBits,
             ZExt32, // Register contains zero-extended contents of stack slot.
             Match32 // Low 32 bits of register match low 32 bits of stack slot.
         };

         RegSlot()
         {
         }

         RegSlot(Reg reg, StackSlot* slot, Mode mode)
             : slot(slot)
             , reg(reg)
             , mode(mode)
         {
         }

         explicit operator bool() const
         {
             return slot && reg;
         }

         bool operator==(const RegSlot& other) const
         {
             return slot == other.slot
                 && reg == other.reg
                 && mode == other.mode;
         }

         void dump(PrintStream& out) const
         {
             out.print(pointerDump(slot), "->", reg);
             switch (mode) {
             case AllBits:
                 out.print("(AllBits)");
                 break;
             case ZExt32:
                 out.print("(ZExt32)");
                 break;
             case Match32:
                 out.print("(Match32)");
                 break;
             }
         }

         StackSlot* slot { nullptr };
         Reg reg;
         Mode mode { AllBits };
     };

     struct SlotConst {
         SlotConst()
         {
         }

         SlotConst(StackSlot* slot, int64_t constant)
             : slot(slot)
             , constant(constant)
         {
         }

         explicit operator bool() const
         {
             return slot;
         }

         bool operator==(const SlotConst& other) const
         {
             return slot == other.slot
                 && constant == other.constant;
         }

         void dump(PrintStream& out) const
         {
             out.print(pointerDump(slot), "->", constant);
         }

         StackSlot* slot { nullptr };
         int64_t constant { 0 };
     };

     struct State {
         void addAlias(const RegConst& newAlias)
         {
             return regConst.append(newAlias);
         }
         void addAlias(const RegSlot& newAlias)
         {
             return regSlot.append(newAlias);
         }
         void addAlias(const SlotConst& newAlias)
         {
             return slotConst.append(newAlias);
         }

         bool contains(const RegConst& alias)
         {
             return regConst.contains(alias);
         }
         bool contains(const RegSlot& alias)
         {
             return regSlot.contains(alias);
         }
         bool contains(const SlotConst& alias)
         {
             return slotConst.contains(alias);
         }

         const RegConst* getRegConst(Reg reg) const
         {
             for (const RegConst& alias : regConst) {
                 if (alias.reg == reg)
                     return &alias;
             }
             return nullptr;
         }

         const RegSlot* getRegSlot(Reg reg) const
         {
             for (const RegSlot& alias : regSlot) {
                 if (alias.reg == reg)
                     return &alias;
             }
             return nullptr;
         }

         const RegSlot* getRegSlot(StackSlot* slot) const
         {
             for (const RegSlot& alias : regSlot) {
                 if (alias.slot == slot)
                     return &alias;
             }
             return nullptr;
         }

         const RegSlot* getRegSlot(Reg reg, StackSlot* slot) const
         {
             for (const RegSlot& alias : regSlot) {
                 if (alias.reg == reg && alias.slot == slot)
                     return &alias;
             }
             return nullptr;
         }

         const SlotConst* getSlotConst(StackSlot* slot) const
         {
             for (const SlotConst& alias : slotConst) {
                 if (alias.slot == slot)
                     return &alias;
             }
             return nullptr;
         }

         Optional<int64_t> constantFor(const Arg& arg)
         {
             if (arg.isReg()) {
                 if (const RegConst* alias = getRegConst(arg.reg()))
                     return alias->constant;
                 return WTF::nullopt;
             }
             if (arg.isStack()) {
                 if (const SlotConst* alias = getSlotConst(arg.stackSlot()))
                     return alias->constant;
                 return WTF::nullopt;
             }
             return WTF::nullopt;
         }

         void clobber(const Arg& arg)
         {
             if (arg.isReg()) {
                 regConst.removeAllMatching(
                     [&] (const RegConst& alias) -> bool {
                         return alias.reg == arg.reg();
                     });
                 regSlot.removeAllMatching(
                     [&] (const RegSlot& alias) -> bool {
                         return alias.reg == arg.reg();
                     });
                 return;
             }
             if (arg.isStack()) {
                 slotConst.removeAllMatching(
                     [&] (const SlotConst& alias) -> bool {
                         return alias.slot == arg.stackSlot();
                     });
                 regSlot.removeAllMatching(
                     [&] (const RegSlot& alias) -> bool {
                         return alias.slot == arg.stackSlot();
                     });
             }
         }

         bool merge(const State& other)
         {
             bool changed = false;

             changed |= !!regConst.removeAllMatching(
                 [&] (RegConst& alias) -> bool {
                     const RegConst* otherAlias = other.getRegConst(alias.reg);
                     if (!otherAlias)
                         return true;
                     if (alias.constant != otherAlias->constant)
                         return true;
                     return false;
                 });

             changed |= !!slotConst.removeAllMatching(
                 [&] (SlotConst& alias) -> bool {
                     const SlotConst* otherAlias = other.getSlotConst(alias.slot);
                     if (!otherAlias)
                         return true;
                     if (alias.constant != otherAlias->constant)
                         return true;
                     return false;
                 });

             changed |= !!regSlot.removeAllMatching(
                 [&] (RegSlot& alias) -> bool {
                     const RegSlot* otherAlias = other.getRegSlot(alias.reg, alias.slot);
                     if (!otherAlias)
                         return true;
                     if (alias.mode != RegSlot::Match32 && alias.mode != otherAlias->mode) {
                         alias.mode = RegSlot::Match32;
                         changed = true;
                     }
                     return false;
                 });

             return changed;
         }

         void dump(PrintStream& out) const
         {
             out.print(
                 "{regConst = [", listDump(regConst), "], slotConst = [", listDump(slotConst),
                 "], regSlot = [", listDump(regSlot), "], wasVisited = ", wasVisited, "}");
         }

         Vector<RegConst> regConst;
         Vector<SlotConst> slotConst;
         Vector<RegSlot> regSlot;
         bool wasVisited { false };
     };

     Code& m_code;
     IndexMap<BasicBlock*, State> m_atHead;
     State m_state;
     BasicBlock* m_block { nullptr };
     unsigned m_instIndex { 0 };
 };

 } // anonymous namespace

 void fixObviousSpills(Code& code)
 {
     PhaseScope phaseScope(code, "fixObviousSpills");

     FixObviousSpills fixObviousSpills(code);
     fixObviousSpills.run();
 }

 } } } // namespace JSC::B3::Air

 #endif // ENABLE(B3_JIT)
	/*
	* Copyright (C) 2016-2017 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.
	*/

	#include "config.h"
	#include "AirFixObviousSpills.h"

	#if ENABLE(B3_JIT)

	#include "AirArgInlines.h"
	#include "AirCode.h"
	#include "AirInstInlines.h"
	#include "AirPhaseScope.h"
	#include <wtf/IndexMap.h>
	#include <wtf/ListDump.h>

	namespace JSC { namespace B3 { namespace Air {

	namespace {

	namespace AirFixObviousSpillsInternal {
	static const bool verbose = false;
	}

	class FixObviousSpills {
	public:
	FixObviousSpills(Code& code)
	: m_code(code)
	, m_atHead(code.size())
	{
	}

	void run()
	{
	if (AirFixObviousSpillsInternal::verbose)
	dataLog("Code before fixObviousSpills:\n", m_code);

	computeAliases();
	fixCode();
	}

	private:
	void computeAliases()
	{
	m_atHead[m_code[0]].wasVisited = true;

	bool changed = true;
	while (changed) {
	changed = false;

	for (BasicBlock* block : m_code) {
	m_block = block;
	m_state = m_atHead[block];
	if (!m_state.wasVisited)
	continue;

	if (AirFixObviousSpillsInternal::verbose)
	dataLog("Executing block ", *m_block, ": ", m_state, "\n");

	for (m_instIndex = 0; m_instIndex < block->size(); ++m_instIndex)
	executeInst();

	for (BasicBlock* successor : block->successorBlocks()) {
	State& toState = m_atHead[successor];
	if (toState.wasVisited)
	changed \|= toState.merge(m_state);
	else {
	toState = m_state;
	changed = true;
	}
	}
	}
	}
	}

	void fixCode()
	{
	for (BasicBlock* block : m_code) {
	m_block = block;
	m_state = m_atHead[block];
	RELEASE_ASSERT(m_state.wasVisited);

	for (m_instIndex = 0; m_instIndex < block->size(); ++m_instIndex) {
	fixInst();
	executeInst();
	}
	}
	}

	template<typename Func>
	void forAllAliases(const Func& func)
	{
	Inst& inst = m_block->at(m_instIndex);

	switch (inst.kind.opcode) {
	case Move:
	if (inst.args[0].isSomeImm()) {
	if (inst.args[1].isReg())
	func(RegConst(inst.args[1].reg(), inst.args[0].value()));
	else if (isSpillSlot(inst.args[1]))
	func(SlotConst(inst.args[1].stackSlot(), inst.args[0].value()));
	} else if (isSpillSlot(inst.args[0]) && inst.args[1].isReg()) {
	if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
	func(RegConst(inst.args[1].reg(), *constant));
	func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::AllBits));
	} else if (inst.args[0].isReg() && isSpillSlot(inst.args[1])) {
	if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
	func(SlotConst(inst.args[1].stackSlot(), *constant));
	func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::AllBits));
	}
	break;

	case Move32:
	if (inst.args[0].isSomeImm()) {
	if (inst.args[1].isReg())
	func(RegConst(inst.args[1].reg(), static_cast<uint32_t>(inst.args[0].value())));
	else if (isSpillSlot(inst.args[1]))
	func(SlotConst(inst.args[1].stackSlot(), static_cast<uint32_t>(inst.args[0].value())));
	} else if (isSpillSlot(inst.args[0]) && inst.args[1].isReg()) {
	if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
	func(RegConst(inst.args[1].reg(), static_cast<uint32_t>(*constant)));
	func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::ZExt32));
	} else if (inst.args[0].isReg() && isSpillSlot(inst.args[1])) {
	if (Optional<int64_t> constant = m_state.constantFor(inst.args[0]))
	func(SlotConst(inst.args[1].stackSlot(), static_cast<int32_t>(*constant)));
	func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::Match32));
	}
	break;

	case MoveFloat:
	if (isSpillSlot(inst.args[0]) && inst.args[1].isReg())
	func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::Match32));
	else if (inst.args[0].isReg() && isSpillSlot(inst.args[1]))
	func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::Match32));
	break;

	case MoveDouble:
	if (isSpillSlot(inst.args[0]) && inst.args[1].isReg())
	func(RegSlot(inst.args[1].reg(), inst.args[0].stackSlot(), RegSlot::AllBits));
	else if (inst.args[0].isReg() && isSpillSlot(inst.args[1]))
	func(RegSlot(inst.args[0].reg(), inst.args[1].stackSlot(), RegSlot::AllBits));
	break;

	default:
	break;
	}
	}

	void executeInst()
	{
	Inst& inst = m_block->at(m_instIndex);

	if (AirFixObviousSpillsInternal::verbose)
	dataLog(" Executing ", inst, ": ", m_state, "\n");

	Inst::forEachDefWithExtraClobberedRegs<Arg>(
	&inst, &inst,
	[&] (const Arg& arg, Arg::Role, Bank, Width) {
	if (AirFixObviousSpillsInternal::verbose)
	dataLog(" Clobbering ", arg, "\n");
	m_state.clobber(arg);
	});

	forAllAliases(
	[&] (const auto& alias) {
	m_state.addAlias(alias);
	});
	}

	void fixInst()
	{
	Inst& inst = m_block->at(m_instIndex);

	if (AirFixObviousSpillsInternal::verbose)
	dataLog("Fixing inst ", inst, ": ", m_state, "\n");

	// Check if alias analysis says that this is unnecessary.
	bool shouldLive = true;
	forAllAliases(
	[&] (const auto& alias) {
	shouldLive &= !m_state.contains(alias);
	});
	if (!shouldLive) {
	inst = Inst();
	return;
	}

	// First handle some special instructions.
	switch (inst.kind.opcode) {
	case Move: {
	if (inst.args[0].isBigImm() && inst.args[1].isReg()
	&& isValidForm(Add64, Arg::Imm, Arg::Tmp, Arg::Tmp)) {
	// BigImm materializations are super expensive on both x86 and ARM. Let's try to
	// materialize this bad boy using math instead. Note that we use unsigned math here
	// since it's more deterministic.
	uint64_t myValue = inst.args[0].value();
	Reg myDest = inst.args[1].reg();
	for (const RegConst& regConst : m_state.regConst) {
	uint64_t otherValue = regConst.constant;

	// Let's try add. That's the only thing that works on all platforms, since it's
	// the only cheap arithmetic op that x86 does in three operands. Long term, we
	// should add fancier materializations here for ARM if the BigImm is yuge.
	uint64_t delta = myValue - otherValue;

	if (Arg::isValidImmForm(delta)) {
	inst.kind = Add64;
	inst.args.resize(3);
	inst.args[0] = Arg::imm(delta);
	inst.args[1] = Tmp(regConst.reg);
	inst.args[2] = Tmp(myDest);
	return;
	}
	}
	return;
	}
	break;
	}

	default:
	break;
	}

	// FIXME: This code should be taught how to simplify the spill-to-spill move
	// instruction. Basically it needs to know to remove the scratch arg.
	// https://bugs.webkit.org/show_bug.cgi?id=171133

	// Create a copy in case we invalidate the instruction. That doesn't happen often.
	Inst instCopy = inst;

	// The goal is to replace references to stack slots. We only care about early uses. We can't
	// handle UseDefs. We could teach this to handle UseDefs if we inserted a store instruction
	// after and we proved that the register aliased to the stack slot dies here. We can get that
	// information from the liveness analysis. We also can't handle late uses, because we don't
	// look at late clobbers when doing this.
	bool didThings = false;
	auto handleArg = [&] (Arg& arg, Arg::Role role, Bank, Width width) {
	if (!isSpillSlot(arg))
	return;
	if (!Arg::isEarlyUse(role))
	return;
	if (Arg::isAnyDef(role))
	return;

	// Try to get a register if at all possible.
	if (const RegSlot* alias = m_state.getRegSlot(arg.stackSlot())) {
	switch (width) {
	case Width64:
	if (alias->mode != RegSlot::AllBits)
	return;
	if (AirFixObviousSpillsInternal::verbose)
	dataLog(" Replacing ", arg, " with ", alias->reg, "\n");
	arg = Tmp(alias->reg);
	didThings = true;
	return;
	case Width32:
	if (AirFixObviousSpillsInternal::verbose)
	dataLog(" Replacing ", arg, " with ", alias->reg, " (subwidth case)\n");
	arg = Tmp(alias->reg);
	didThings = true;
	return;
	default:
	return;
	}
	}

	// Revert to immediate if that didn't work.
	if (const SlotConst* alias = m_state.getSlotConst(arg.stackSlot())) {
	if (AirFixObviousSpillsInternal::verbose)
	dataLog(" Replacing ", arg, " with constant ", alias->constant, "\n");
	if (Arg::isValidImmForm(alias->constant))
	arg = Arg::imm(alias->constant);
	else
	arg = Arg::bigImm(alias->constant);
	didThings = true;
	return;
	}
	};

	inst.forEachArg(handleArg);
	if (!didThings \|\| inst.isValidForm())
	return;

	// We introduced something invalid along the way. Back up and carefully handle each argument.
	inst = instCopy;
	ASSERT(inst.isValidForm());
	inst.forEachArg(
	[&] (Arg& arg, Arg::Role role, Bank bank, Width width) {
	Arg argCopy = arg;
	handleArg(arg, role, bank, width);
	if (!inst.isValidForm())
	arg = argCopy;
	});
	}

	static bool isSpillSlot(const Arg& arg)
	{
	return arg.isStack() && arg.stackSlot()->isSpill();
	}

	struct RegConst {
	RegConst()
	{
	}

	RegConst(Reg reg, int64_t constant)
	: reg(reg)
	, constant(constant)
	{
	}

	explicit operator bool() const
	{
	return !!reg;
	}

	bool operator==(const RegConst& other) const
	{
	return reg == other.reg
	&& constant == other.constant;
	}

	void dump(PrintStream& out) const
	{
	out.print(reg, "->", constant);
	}

	Reg reg;
	int64_t constant { 0 };
	};

	struct RegSlot {
	enum Mode : int8_t {
	AllBits,
	ZExt32, // Register contains zero-extended contents of stack slot.
	Match32 // Low 32 bits of register match low 32 bits of stack slot.
	};

	RegSlot()
	{
	}

	RegSlot(Reg reg, StackSlot* slot, Mode mode)
	: slot(slot)
	, reg(reg)
	, mode(mode)
	{
	}

	explicit operator bool() const
	{
	return slot && reg;
	}

	bool operator==(const RegSlot& other) const
	{
	return slot == other.slot
	&& reg == other.reg
	&& mode == other.mode;
	}

	void dump(PrintStream& out) const
	{
	out.print(pointerDump(slot), "->", reg);
	switch (mode) {
	case AllBits:
	out.print("(AllBits)");
	break;
	case ZExt32:
	out.print("(ZExt32)");
	break;
	case Match32:
	out.print("(Match32)");
	break;
	}
	}

	StackSlot* slot { nullptr };
	Reg reg;
	Mode mode { AllBits };
	};

	struct SlotConst {
	SlotConst()
	{
	}

	SlotConst(StackSlot* slot, int64_t constant)
	: slot(slot)
	, constant(constant)
	{
	}

	explicit operator bool() const
	{
	return slot;
	}

	bool operator==(const SlotConst& other) const
	{
	return slot == other.slot
	&& constant == other.constant;
	}

	void dump(PrintStream& out) const
	{
	out.print(pointerDump(slot), "->", constant);
	}

	StackSlot* slot { nullptr };
	int64_t constant { 0 };
	};

	struct State {
	void addAlias(const RegConst& newAlias)
	{
	return regConst.append(newAlias);
	}
	void addAlias(const RegSlot& newAlias)
	{
	return regSlot.append(newAlias);
	}
	void addAlias(const SlotConst& newAlias)
	{
	return slotConst.append(newAlias);
	}

	bool contains(const RegConst& alias)
	{
	return regConst.contains(alias);
	}
	bool contains(const RegSlot& alias)
	{
	return regSlot.contains(alias);
	}
	bool contains(const SlotConst& alias)
	{
	return slotConst.contains(alias);
	}

	const RegConst* getRegConst(Reg reg) const
	{
	for (const RegConst& alias : regConst) {
	if (alias.reg == reg)
	return &alias;
	}
	return nullptr;
	}

	const RegSlot* getRegSlot(Reg reg) const
	{
	for (const RegSlot& alias : regSlot) {
	if (alias.reg == reg)
	return &alias;
	}
	return nullptr;
	}

	const RegSlot* getRegSlot(StackSlot* slot) const
	{
	for (const RegSlot& alias : regSlot) {
	if (alias.slot == slot)
	return &alias;
	}
	return nullptr;
	}

	const RegSlot* getRegSlot(Reg reg, StackSlot* slot) const
	{
	for (const RegSlot& alias : regSlot) {
	if (alias.reg == reg && alias.slot == slot)
	return &alias;
	}
	return nullptr;
	}

	const SlotConst* getSlotConst(StackSlot* slot) const
	{
	for (const SlotConst& alias : slotConst) {
	if (alias.slot == slot)
	return &alias;
	}
	return nullptr;
	}

	Optional<int64_t> constantFor(const Arg& arg)
	{
	if (arg.isReg()) {
	if (const RegConst* alias = getRegConst(arg.reg()))
	return alias->constant;
	return WTF::nullopt;
	}
	if (arg.isStack()) {
	if (const SlotConst* alias = getSlotConst(arg.stackSlot()))
	return alias->constant;
	return WTF::nullopt;
	}
	return WTF::nullopt;
	}

	void clobber(const Arg& arg)
	{
	if (arg.isReg()) {
	regConst.removeAllMatching(
	[&] (const RegConst& alias) -> bool {
	return alias.reg == arg.reg();
	});
	regSlot.removeAllMatching(
	[&] (const RegSlot& alias) -> bool {
	return alias.reg == arg.reg();
	});
	return;
	}
	if (arg.isStack()) {
	slotConst.removeAllMatching(
	[&] (const SlotConst& alias) -> bool {
	return alias.slot == arg.stackSlot();
	});
	regSlot.removeAllMatching(
	[&] (const RegSlot& alias) -> bool {
	return alias.slot == arg.stackSlot();
	});
	}
	}

	bool merge(const State& other)
	{
	bool changed = false;

	changed \|= !!regConst.removeAllMatching(
	[&] (RegConst& alias) -> bool {
	const RegConst* otherAlias = other.getRegConst(alias.reg);
	if (!otherAlias)
	return true;
	if (alias.constant != otherAlias->constant)
	return true;
	return false;
	});

	changed \|= !!slotConst.removeAllMatching(
	[&] (SlotConst& alias) -> bool {
	const SlotConst* otherAlias = other.getSlotConst(alias.slot);
	if (!otherAlias)
	return true;
	if (alias.constant != otherAlias->constant)
	return true;
	return false;
	});

	changed \|= !!regSlot.removeAllMatching(
	[&] (RegSlot& alias) -> bool {
	const RegSlot* otherAlias = other.getRegSlot(alias.reg, alias.slot);
	if (!otherAlias)
	return true;
	if (alias.mode != RegSlot::Match32 && alias.mode != otherAlias->mode) {
	alias.mode = RegSlot::Match32;
	changed = true;
	}
	return false;
	});

	return changed;
	}

	void dump(PrintStream& out) const
	{
	out.print(
	"{regConst = [", listDump(regConst), "], slotConst = [", listDump(slotConst),
	"], regSlot = [", listDump(regSlot), "], wasVisited = ", wasVisited, "}");
	}

	Vector<RegConst> regConst;
	Vector<SlotConst> slotConst;
	Vector<RegSlot> regSlot;
	bool wasVisited { false };
	};

	Code& m_code;
	IndexMap<BasicBlock*, State> m_atHead;
	State m_state;
	BasicBlock* m_block { nullptr };
	unsigned m_instIndex { 0 };
	};

	} // anonymous namespace

	void fixObviousSpills(Code& code)
	{
	PhaseScope phaseScope(code, "fixObviousSpills");

	FixObviousSpills fixObviousSpills(code);
	fixObviousSpills.run();
	}

	} } } // namespace JSC::B3::Air

	#endif // ENABLE(B3_JIT)