AirGenerate.cpp   [plain text]

/*
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#include "config.h"
#include "AirGenerate.h"

#if ENABLE(B3_JIT)

#include "AirAllocateStack.h"
#include "AirCode.h"
#include "AirDumpAsJS.h"
#include "AirEliminateDeadCode.h"
#include "AirFixObviousSpills.h"
#include "AirFixPartialRegisterStalls.h"
#include "AirGenerationContext.h"
#include "AirHandleCalleeSaves.h"
#include "AirIteratedRegisterCoalescing.h"
#include "AirLogRegisterPressure.h"
#include "AirLowerAfterRegAlloc.h"
#include "AirLowerMacros.h"
#include "AirOpcodeUtils.h"
#include "AirOptimizeBlockOrder.h"
#include "AirReportUsedRegisters.h"
#include "AirSimplifyCFG.h"
#include "AirSpillEverything.h"
#include "AirValidate.h"
#include "B3Common.h"
#include "B3IndexMap.h"
#include "B3Procedure.h"
#include "B3TimingScope.h"
#include "CCallHelpers.h"
#include "DisallowMacroScratchRegisterUsage.h"

namespace JSC { namespace B3 { namespace Air {

void prepareForGeneration(Code& code)
{
    TimingScope timingScope("Air::prepareForGeneration");
    
    // We don't expect the incoming code to have predecessors computed.
    code.resetReachability();
    
    if (shouldValidateIR())
        validate(code);

    // If we're doing super verbose dumping, the phase scope of any phase will already do a dump.
    if (shouldDumpIR(AirMode) && !shouldDumpIRAtEachPhase(AirMode)) {
        dataLog("Initial air:\n");
        dataLog(code);
    }

    lowerMacros(code);

    // This is where we run our optimizations and transformations.
    // FIXME: Add Air optimizations.
    // https://bugs.webkit.org/show_bug.cgi?id=150456
    
    eliminateDeadCode(code);

    // Register allocation for all the Tmps that do not have a corresponding machine register.
    // After this phase, every Tmp has a reg.
    //
    // For debugging, you can use spillEverything() to put everything to the stack between each Inst.
    if (Options::airSpillsEverything())
        spillEverything(code);
    else
        iteratedRegisterCoalescing(code);

    if (Options::logAirRegisterPressure()) {
        dataLog("Register pressure after register allocation:\n");
        logRegisterPressure(code);
    }

    // This replaces uses of spill slots with registers or constants if possible. It does this by
    // minimizing the amount that we perturb the already-chosen register allocation. It may extend
    // the live ranges of registers though.
    fixObviousSpills(code);

    lowerAfterRegAlloc(code);

    // Prior to this point the prologue and epilogue is implicit. This makes it explicit. It also
    // does things like identify which callee-saves we're using and saves them.
    handleCalleeSaves(code);
    
    if (Options::dumpAirAsJSBeforeAllocateStack()) {
        dataLog("Dumping Air as JS before allocateStack:\n");
        dumpAsJS(code, WTF::dataFile());
        dataLog("Air hash: ", code.jsHash(), "\n");
    }

    // This turns all Stack and CallArg Args into Addr args that use the frame pointer. It does
    // this by first-fit allocating stack slots. It should be pretty darn close to optimal, so we
    // shouldn't have to worry about this very much.
    allocateStack(code);
    
    if (Options::dumpAirAfterAllocateStack()) {
        dataLog("Dumping Air after allocateStack:\n");
        dataLog(code);
        dataLog("Air hash: ", code.jsHash(), "\n");
    }

    // If we coalesced moves then we can unbreak critical edges. This is the main reason for this
    // phase.
    simplifyCFG(code);

    // This sorts the basic blocks in Code to achieve an ordering that maximizes the likelihood that a high
    // frequency successor is also the fall-through target.
    optimizeBlockOrder(code);

    // This is needed to satisfy a requirement of B3::StackmapValue.
    reportUsedRegisters(code);

    // Attempt to remove false dependencies between instructions created by partial register changes.
    // This must be executed as late as possible as it depends on the instructions order and register
    // use. We _must_ run this after reportUsedRegisters(), since that kills variable assignments
    // that seem dead. Luckily, this phase does not change register liveness, so that's OK.
    fixPartialRegisterStalls(code);

    if (shouldValidateIR())
        validate(code);

    // Do a final dump of Air. Note that we have to do this even if we are doing per-phase dumping,
    // since the final generation is not a phase.
    if (shouldDumpIR(AirMode)) {
        dataLog("Air after ", code.lastPhaseName(), ", before generation:\n");
        dataLog(code);
    }
}

void generate(Code& code, CCallHelpers& jit)
{
    TimingScope timingScope("Air::generate");

    DisallowMacroScratchRegisterUsage disallowScratch(jit);

    // And now, we generate code.
    jit.emitFunctionPrologue();
    if (code.frameSize())
        jit.addPtr(CCallHelpers::TrustedImm32(-code.frameSize()), MacroAssembler::stackPointerRegister);

    auto argFor = [&] (const RegisterAtOffset& entry) -> CCallHelpers::Address {
        return CCallHelpers::Address(GPRInfo::callFrameRegister, entry.offset());
    };
    
    for (const RegisterAtOffset& entry : code.calleeSaveRegisters()) {
        if (entry.reg().isGPR())
            jit.storePtr(entry.reg().gpr(), argFor(entry));
        else
            jit.storeDouble(entry.reg().fpr(), argFor(entry));
    }

    GenerationContext context;
    context.code = &code;
    IndexMap<BasicBlock, CCallHelpers::Label> blockLabels(code.size());
    IndexMap<BasicBlock, CCallHelpers::JumpList> blockJumps(code.size());

    auto link = [&] (CCallHelpers::Jump jump, BasicBlock* target) {
        if (blockLabels[target].isSet()) {
            jump.linkTo(blockLabels[target], &jit);
            return;
        }

        blockJumps[target].append(jump);
    };

    PCToOriginMap& pcToOriginMap = code.proc().pcToOriginMap();
    auto addItem = [&] (Inst& inst) {
        if (!inst.origin) {
            pcToOriginMap.appendItem(jit.label(), Origin());
            return;
        }
        pcToOriginMap.appendItem(jit.label(), inst.origin->origin());
    };

    for (BasicBlock* block : code) {
        blockJumps[block].link(&jit);
        blockLabels[block] = jit.label();
        ASSERT(block->size() >= 1);
        for (unsigned i = 0; i < block->size() - 1; ++i) {
            Inst& inst = block->at(i);
            addItem(inst);
            CCallHelpers::Jump jump = inst.generate(jit, context);
            ASSERT_UNUSED(jump, !jump.isSet());
        }

        if (block->last().opcode == Jump
            && block->successorBlock(0) == code.findNextBlock(block))
            continue;

        addItem(block->last());

        if (isReturn(block->last().opcode)) {
            // We currently don't represent the full prologue/epilogue in Air, so we need to
            // have this override.
            if (code.frameSize()) {
                for (const RegisterAtOffset& entry : code.calleeSaveRegisters()) {
                    if (entry.reg().isGPR())
                        jit.loadPtr(argFor(entry), entry.reg().gpr());
                    else
                        jit.loadDouble(argFor(entry), entry.reg().fpr());
                }
                jit.emitFunctionEpilogue();
            } else
                jit.emitFunctionEpilogueWithEmptyFrame();
            jit.ret();
            addItem(block->last());
            continue;
        }

        CCallHelpers::Jump jump = block->last().generate(jit, context);
        switch (block->numSuccessors()) {
        case 0:
            ASSERT(!jump.isSet());
            break;
        case 1:
            link(jump, block->successorBlock(0));
            break;
        case 2:
            link(jump, block->successorBlock(0));
            if (block->successorBlock(1) != code.findNextBlock(block))
                link(jit.jump(), block->successorBlock(1));
            break;
        default:
            RELEASE_ASSERT_NOT_REACHED();
            break;
        }
        addItem(block->last());
    }

    pcToOriginMap.appendItem(jit.label(), Origin());
    // FIXME: Make late paths have Origins: https://bugs.webkit.org/show_bug.cgi?id=153689
    for (auto& latePath : context.latePaths)
        latePath->run(jit, context);
    pcToOriginMap.appendItem(jit.label(), Origin());
}

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

#endif // ENABLE(B3_JIT)