ppsspp/Core/MIPS/x86/CompBranch.cpp

// Copyright (c) 2012- PPSSPP Project.

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, version 2.0 or later versions.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License 2.0 for more details.

// A copy of the GPL 2.0 should have been included with the program.
// If not, see http://www.gnu.org/licenses/

// Official git repository and contact information can be found at
// https://github.com/hrydgard/ppsspp and http://www.ppsspp.org/.

#include "Core/Reporting.h"
#include "Core/Config.h"
#include "Core/HLE/HLE.h"
#include "Core/HLE/HLETables.h"
#include "Core/Host.h"

#include "Core/MIPS/MIPS.h"
#include "Core/MIPS/MIPSCodeUtils.h"
#include "Core/MIPS/MIPSAnalyst.h"
#include "Core/MIPS/MIPSTables.h"

#include "Core/MIPS/x86/Jit.h"
#include "Core/MIPS/x86/RegCache.h"
#include "Core/MIPS/JitCommon/JitBlockCache.h"

#define _RS MIPS_GET_RS(op)
#define _RT MIPS_GET_RT(op)
#define _RD MIPS_GET_RD(op)
#define _FS MIPS_GET_FS(op)
#define _FT MIPS_GET_FT(op)
#define _FD MIPS_GET_FD(op)
#define _SA MIPS_GET_SA(op)
#define _POS  ((op>> 6) & 0x1F)
#define _SIZE ((op>>11) & 0x1F)
#define _IMM16 (signed short)(op & 0xFFFF)
#define _IMM26 (op & 0x03FFFFFF)

#define LOOPOPTIMIZATION 0

using namespace MIPSAnalyst;

// NOTE: Can't use CONDITIONAL_DISABLE in this file, branches are so special
// that they cannot be interpreted in the context of the Jit.

// But we can at least log and compare.
// #define DO_CONDITIONAL_LOG 1
#define DO_CONDITIONAL_LOG 0

// We can also disable nice delay slots.
// #define CONDITIONAL_NICE_DELAYSLOT delaySlotIsNice = false;
#define CONDITIONAL_NICE_DELAYSLOT ;

#if DO_CONDITIONAL_LOG
#define CONDITIONAL_LOG BranchLog(op);
#define CONDITIONAL_LOG_EXIT(addr) BranchLogExit(op, addr, false);
#define CONDITIONAL_LOG_EXIT_EAX() BranchLogExit(op, 0, true);
#else
#define CONDITIONAL_LOG ;
#define CONDITIONAL_LOG_EXIT(addr) ;
#define CONDITIONAL_LOG_EXIT_EAX() ;
#endif

namespace MIPSComp
{

static u32 intBranchExit;
static u32 jitBranchExit;

static void JitBranchLog(MIPSOpcode op, u32 pc)
{
	currentMIPS->pc = pc;
	currentMIPS->inDelaySlot = false;

	MIPSInterpretFunc func = MIPSGetInterpretFunc(op);
	MIPSInfo info = MIPSGetInfo(op);
	func(op);

	// Branch taken, use nextPC.
	if (currentMIPS->inDelaySlot)
		intBranchExit = currentMIPS->nextPC;
	else
	{
		// Branch not taken, likely delay slot skipped.
		if (info & LIKELY)
			intBranchExit = currentMIPS->pc;
		// Branch not taken, so increment over delay slot.
		else
			intBranchExit = currentMIPS->pc + 4;
	}

	currentMIPS->pc = pc;
	currentMIPS->inDelaySlot = false;
}

static void JitBranchLogMismatch(MIPSOpcode op, u32 pc)
{
	char temp[256];
	MIPSDisAsm(op, pc, temp, true);
	ERROR_LOG(JIT, "Bad jump: %s - int:%08x jit:%08x", temp, intBranchExit, jitBranchExit);
	host->SetDebugMode(true);
}

void Jit::BranchLog(MIPSOpcode op)
{
	FlushAll();
	ABI_CallFunctionCC(thunks.ProtectFunction((void *) &JitBranchLog, 2), op.encoding, js.compilerPC);
}

void Jit::BranchLogExit(MIPSOpcode op, u32 dest, bool useEAX)
{
	OpArg destArg = useEAX ? R(EAX) : Imm32(dest);

	CMP(32, M((void *) &intBranchExit), destArg);
	FixupBranch skip = J_CC(CC_E);

	MOV(32, M((void *) &jitBranchExit), destArg);
	ABI_CallFunctionCC(thunks.ProtectFunction((void *) &JitBranchLogMismatch, 2), op.encoding, js.compilerPC);
	// Restore EAX, we probably ruined it.
	if (useEAX)
		MOV(32, R(EAX), M((void *) &jitBranchExit));

	SetJumpTarget(skip);
}

static CCFlags FlipCCFlag(CCFlags flag)
{
	switch (flag)
	{
	case CC_O: return CC_NO;
	case CC_NO: return CC_O;
	case CC_B: return CC_NB;
	case CC_NB: return CC_B;
	case CC_Z: return CC_NZ;
	case CC_NZ: return CC_Z;
	case CC_BE: return CC_NBE;
	case CC_NBE: return CC_BE;
	case CC_S: return CC_NS;
	case CC_NS: return CC_S;
	case CC_P: return CC_NP;
	case CC_NP: return CC_P;
	case CC_L: return CC_NL;
	case CC_NL: return CC_L;
	case CC_LE: return CC_NLE;
	case CC_NLE: return CC_LE;
	}
	ERROR_LOG_REPORT(JIT, false, "FlipCCFlag: Unexpected CC flag: %d", flag);
	return CC_O;
}

bool Jit::PredictTakeBranch(u32 targetAddr, bool likely) {
	// If it's likely, it's... probably likely, right?
	if (likely)
		return true;

	// TODO: Normal branch prediction would be to take branches going upward to lower addresses.
	// However, this results in worse performance as of this comment's writing.
	// The reverse check generally gives better or same performance.
	return targetAddr > js.compilerPC;
}

void Jit::CompBranchExits(CCFlags cc, u32 targetAddr, u32 notTakenAddr, bool delaySlotIsNice, bool likely, bool andLink) {
	// We may want to try to continue along this branch a little while, to reduce reg flushing.
	if (CanContinueBranch())
	{
		bool predictTakeBranch = PredictTakeBranch(targetAddr, likely);
		if (predictTakeBranch)
			cc = FlipCCFlag(cc);

		Gen::FixupBranch ptr;
		RegCacheState state;
		if (!likely)
		{
			if (!delaySlotIsNice)
				CompileDelaySlot(DELAYSLOT_SAFE);
			ptr = J_CC(cc, true);
			GetStateAndFlushAll(state);
		}
		else
		{
			ptr = J_CC(cc, true);
			if (predictTakeBranch)
				GetStateAndFlushAll(state);
			else
				CompileDelaySlot(DELAYSLOT_FLUSH);
		}

		if (predictTakeBranch)
		{
			// We flipped the cc, the not taken case is first.
			CONDITIONAL_LOG_EXIT(notTakenAddr);
			WriteExit(notTakenAddr, js.nextExit++);

			// Now our taken path.  Bring the regs back, we didn't flush 'em after all.
			SetJumpTarget(ptr);
			RestoreState(state);
			CONDITIONAL_LOG_EXIT(targetAddr);

			if (andLink)
				gpr.SetImm(MIPS_REG_RA, js.compilerPC + 8);

			// Don't forget to run the delay slot if likely.
			if (likely)
				CompileDelaySlot(DELAYSLOT_NICE);

			// Account for the increment in the loop.
			js.compilerPC = targetAddr - 4;
			// In case the delay slot was a break or something.
			js.compiling = true;
		}
		else
		{
			// Take the branch
			if (andLink)
				MOV(32, M(&mips_->r[MIPS_REG_RA]), Imm32(js.compilerPC + 8));
			CONDITIONAL_LOG_EXIT(targetAddr);
			WriteExit(targetAddr, js.nextExit++);

			// Not taken
			SetJumpTarget(ptr);
			RestoreState(state);
			CONDITIONAL_LOG_EXIT(notTakenAddr);

			// Account for the delay slot.
			js.compilerPC += 4;
			// In case the delay slot was a break or something.
			js.compiling = true;
		}
	}
	else
	{
		Gen::FixupBranch ptr;
		if (!likely)
		{
			if (!delaySlotIsNice)
				CompileDelaySlot(DELAYSLOT_SAFE_FLUSH);
			else
				FlushAll();
			ptr = J_CC(cc, true);
		}
		else
		{
			FlushAll();
			ptr = J_CC(cc, true);
			CompileDelaySlot(DELAYSLOT_FLUSH);
		}

		// Take the branch
		if (andLink)
			MOV(32, M(&mips_->r[MIPS_REG_RA]), Imm32(js.compilerPC + 8));
		CONDITIONAL_LOG_EXIT(targetAddr);
		WriteExit(targetAddr, js.nextExit++);

		// Not taken
		SetJumpTarget(ptr);
		CONDITIONAL_LOG_EXIT(notTakenAddr);
		WriteExit(notTakenAddr, js.nextExit++);
		js.compiling = false;
	}
}

void Jit::BranchRSRTComp(MIPSOpcode op, Gen::CCFlags cc, bool likely)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in RSRTComp delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	int offset = _IMM16 << 2;
	MIPSGPReg rt = _RT;
	MIPSGPReg rs = _RS;
	u32 targetAddr = js.compilerPC + offset + 4;

	if (jo.immBranches && gpr.IsImm(rs) && gpr.IsImm(rt) && js.numInstructions < jo.continueMaxInstructions)
	{
		// The cc flags are opposites: when NOT to take the branch.
		bool skipBranch;
		s32 rsImm = (s32)gpr.GetImm(rs);
		s32 rtImm = (s32)gpr.GetImm(rt);

		switch (cc)
		{
		case CC_E: skipBranch = rsImm == rtImm; break;
		case CC_NE: skipBranch = rsImm != rtImm; break;
		default: skipBranch = false; _dbg_assert_msg_(JIT, false, "Bad cc flag in BranchRSRTComp().");
		}

		if (skipBranch)
		{
			// Skip the delay slot if likely, otherwise it'll be the next instruction.
			if (likely)
				js.compilerPC += 4;
			return;
		}

		// Branch taken.  Always compile the delay slot, and then go to dest.
		CompileDelaySlot(DELAYSLOT_NICE);
		// Account for the increment in the loop.
		js.compilerPC = targetAddr - 4;
		// In case the delay slot was a break or something.
		js.compiling = true;
		return;
	}

	MIPSOpcode delaySlotOp = Memory::Read_Instruction(js.compilerPC+4);
	bool delaySlotIsNice = IsDelaySlotNiceReg(op, delaySlotOp, rt, rs);
	CONDITIONAL_NICE_DELAYSLOT;
	if (!likely && delaySlotIsNice)
		CompileDelaySlot(DELAYSLOT_NICE);

	if (gpr.IsImm(rt) && gpr.GetImm(rt) == 0)
	{
		gpr.KillImmediate(rs, true, false);
		CMP(32, gpr.R(rs), Imm32(0));
	}
	else
	{
		gpr.MapReg(rs, true, false);
		CMP(32, gpr.R(rs), gpr.R(rt));
	}

	CompBranchExits(cc, targetAddr, js.compilerPC + 8, delaySlotIsNice, likely, false);
}

void Jit::BranchRSZeroComp(MIPSOpcode op, Gen::CCFlags cc, bool andLink, bool likely)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in RSZeroComp delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	int offset = _IMM16 << 2;
	MIPSGPReg rs = _RS;
	u32 targetAddr = js.compilerPC + offset + 4;

	if (jo.immBranches && gpr.IsImm(rs) && js.numInstructions < jo.continueMaxInstructions)
	{
		// The cc flags are opposites: when NOT to take the branch.
		bool skipBranch;
		s32 imm = (s32)gpr.GetImm(rs);

		switch (cc)
		{
		case CC_G: skipBranch = imm > 0; break;
		case CC_GE: skipBranch = imm >= 0; break;
		case CC_L: skipBranch = imm < 0; break;
		case CC_LE: skipBranch = imm <= 0; break;
		default: skipBranch = false; _dbg_assert_msg_(JIT, false, "Bad cc flag in BranchRSZeroComp().");
		}

		if (skipBranch)
		{
			// Skip the delay slot if likely, otherwise it'll be the next instruction.
			if (likely)
				js.compilerPC += 4;
			return;
		}

		// Branch taken.  Always compile the delay slot, and then go to dest.
		CompileDelaySlot(DELAYSLOT_NICE);
		if (andLink)
			gpr.SetImm(MIPS_REG_RA, js.compilerPC + 8);

		// Account for the increment in the loop.
		js.compilerPC = targetAddr - 4;
		// In case the delay slot was a break or something.
		js.compiling = true;
		return;
	}

	MIPSOpcode delaySlotOp = Memory::Read_Instruction(js.compilerPC + 4);
	bool delaySlotIsNice = IsDelaySlotNiceReg(op, delaySlotOp, rs);
	CONDITIONAL_NICE_DELAYSLOT;
	if (!likely && delaySlotIsNice)
		CompileDelaySlot(DELAYSLOT_NICE);

	gpr.MapReg(rs, true, false);
	CMP(32, gpr.R(rs), Imm32(0));

	CompBranchExits(cc, targetAddr, js.compilerPC + 8, delaySlotIsNice, likely, andLink);
}


void Jit::Comp_RelBranch(MIPSOpcode op)
{
	switch (op>>26) 
	{
	case 4: BranchRSRTComp(op, CC_NZ, false); break;//beq
	case 5: BranchRSRTComp(op, CC_Z,  false); break;//bne

	case 6: BranchRSZeroComp(op, CC_G, false, false); break;//blez
	case 7: BranchRSZeroComp(op, CC_LE, false, false); break;//bgtz

	case 20: BranchRSRTComp(op, CC_NZ, true); break;//beql
	case 21: BranchRSRTComp(op, CC_Z,  true); break;//bnel

	case 22: BranchRSZeroComp(op, CC_G, false, true); break;//blezl
	case 23: BranchRSZeroComp(op, CC_LE, false, true); break;//bgtzl

	default:
		_dbg_assert_msg_(CPU,0,"Trying to compile instruction that can't be compiled");
		break;
	}
}

void Jit::Comp_RelBranchRI(MIPSOpcode op)
{
	switch ((op >> 16) & 0x1F)
	{
	case 0: BranchRSZeroComp(op, CC_GE, false, false); break; //if ((s32)R(rs) <  0) DelayBranchTo(addr); else PC += 4; break;//bltz
	case 1: BranchRSZeroComp(op, CC_L, false, false);  break; //if ((s32)R(rs) >= 0) DelayBranchTo(addr); else PC += 4; break;//bgez
	case 2: BranchRSZeroComp(op, CC_GE, false, true);  break; //if ((s32)R(rs) <  0) DelayBranchTo(addr); else PC += 8; break;//bltzl
	case 3: BranchRSZeroComp(op, CC_L, false, true);   break; //if ((s32)R(rs) >= 0) DelayBranchTo(addr); else PC += 8; break;//bgezl
	case 16: BranchRSZeroComp(op, CC_GE, true, false); break; //R(MIPS_REG_RA) = PC + 8; if ((s32)R(rs) <  0) DelayBranchTo(addr); else PC += 4; break;//bltzal
	case 17: BranchRSZeroComp(op, CC_L, true, false);  break; //R(MIPS_REG_RA) = PC + 8; if ((s32)R(rs) >= 0) DelayBranchTo(addr); else PC += 4; break;//bgezal
	case 18: BranchRSZeroComp(op, CC_GE, true, true);  break; //R(MIPS_REG_RA) = PC + 8; if ((s32)R(rs) <  0) DelayBranchTo(addr); else SkipLikely(); break;//bltzall
	case 19: BranchRSZeroComp(op, CC_L, true, true);   break; //R(MIPS_REG_RA) = PC + 8; if ((s32)R(rs) >= 0) DelayBranchTo(addr); else SkipLikely(); break;//bgezall
	default:
		_dbg_assert_msg_(CPU,0,"Trying to compile instruction that can't be compiled");
		break;
	}
}


// If likely is set, discard the branch slot if NOT taken.
void Jit::BranchFPFlag(MIPSOpcode op, Gen::CCFlags cc, bool likely)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in FPFlag delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	int offset = _IMM16 << 2;
	u32 targetAddr = js.compilerPC + offset + 4;

	MIPSOpcode delaySlotOp = Memory::Read_Instruction(js.compilerPC + 4);
	bool delaySlotIsNice = IsDelaySlotNiceFPU(op, delaySlotOp);
	CONDITIONAL_NICE_DELAYSLOT;
	if (!likely && delaySlotIsNice)
		CompileDelaySlot(DELAYSLOT_NICE);

	TEST(32, M((void *)&(mips_->fpcond)), Imm32(1));

	CompBranchExits(cc, targetAddr, js.compilerPC + 8, delaySlotIsNice, likely, false);
}


void Jit::Comp_FPUBranch(MIPSOpcode op)
{
	switch((op >> 16) & 0x1f)
	{
	case 0:	BranchFPFlag(op, CC_NZ, false); break; //bc1f
	case 1: BranchFPFlag(op, CC_Z,	false); break; //bc1t
	case 2: BranchFPFlag(op, CC_NZ, true);	break; //bc1fl
	case 3: BranchFPFlag(op, CC_Z,	true);	break; //bc1tl
	default:
		_dbg_assert_msg_(CPU,0,"Trying to interpret instruction that can't be interpreted");
		break;
	}
}

// If likely is set, discard the branch slot if NOT taken.
void Jit::BranchVFPUFlag(MIPSOpcode op, Gen::CCFlags cc, bool likely)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in VFPU delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	int offset = _IMM16 << 2;
	u32 targetAddr = js.compilerPC + offset + 4;

	MIPSOpcode delaySlotOp = Memory::Read_Instruction(js.compilerPC + 4);

	// Sometimes there's a VFPU branch in a delay slot (Disgaea 2: Dark Hero Days, Zettai Hero Project, La Pucelle)
	// The behavior is undefined - the CPU may take the second branch even if the first one passes.
	// However, it does consistently try each branch, which these games seem to expect.
	bool delaySlotIsBranch = MIPSCodeUtils::IsVFPUBranch(delaySlotOp);
	bool delaySlotIsNice = !delaySlotIsBranch && IsDelaySlotNiceVFPU(op, delaySlotOp);
	CONDITIONAL_NICE_DELAYSLOT;
	if (!likely && delaySlotIsNice)
		CompileDelaySlot(DELAYSLOT_NICE);
	if (delaySlotIsBranch && (signed short)(delaySlotOp & 0xFFFF) != (signed short)(op & 0xFFFF) - 1)
		ERROR_LOG_REPORT(JIT, "VFPU branch in VFPU delay slot at %08x with different target %d / %d", js.compilerPC, (signed short)(delaySlotOp & 0xFFFF), (signed short)(op & 0xFFFF) - 1);

	// THE CONDITION
	int imm3 = (op >> 18) & 7;

	//int val = (mips_->vfpuCtrl[VFPU_CTRL_CC] >> imm3) & 1;
	TEST(32, M((void *)&(mips_->vfpuCtrl[VFPU_CTRL_CC])), Imm32(1 << imm3));

	u32 notTakenTarget = js.compilerPC + (delaySlotIsBranch ? 4 : 8);
	CompBranchExits(cc, targetAddr, notTakenTarget, delaySlotIsNice, likely, false);
}


void Jit::Comp_VBranch(MIPSOpcode op)
{
	switch ((op >> 16) & 3)
	{
	case 0:	BranchVFPUFlag(op, CC_NZ, false); break; //bvf
	case 1: BranchVFPUFlag(op, CC_Z,	false); break; //bvt
	case 2: BranchVFPUFlag(op, CC_NZ, true);	break; //bvfl
	case 3: BranchVFPUFlag(op, CC_Z,	true);	break; //bvtl
	default:
		_dbg_assert_msg_(CPU,0,"Comp_VBranch: Invalid instruction");
		break;
	}
}

void Jit::Comp_Jump(MIPSOpcode op)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in Jump delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	u32 off = _IMM26 << 2;
	u32 targetAddr = (js.compilerPC & 0xF0000000) | off;

	// Might be a stubbed address or something?
	if (!Memory::IsValidAddress(targetAddr))
	{
		if (js.nextExit == 0)
			ERROR_LOG_REPORT(JIT, "Jump to invalid address: %08x", targetAddr)
		else
			js.compiling = false;
		// TODO: Mark this block dirty or something?  May be indication it will be changed by imports.
		return;
	}

	switch (op >> 26) 
	{
	case 2: //j
		CompileDelaySlot(DELAYSLOT_NICE);
		if (jo.continueJumps && js.numInstructions < jo.continueMaxInstructions)
		{
			// Account for the increment in the loop.
			js.compilerPC = targetAddr - 4;
			// In case the delay slot was a break or something.
			js.compiling = true;
			return;
		}
		FlushAll();
		CONDITIONAL_LOG_EXIT(targetAddr);
		WriteExit(targetAddr, js.nextExit++);
		break;

	case 3: //jal
		// Save return address - might be overwritten by delay slot.
		gpr.SetImm(MIPS_REG_RA, js.compilerPC + 8);
		CompileDelaySlot(DELAYSLOT_NICE);
		if (jo.continueJumps && js.numInstructions < jo.continueMaxInstructions)
		{
			// Account for the increment in the loop.
			js.compilerPC = targetAddr - 4;
			// In case the delay slot was a break or something.
			js.compiling = true;
			return;
		}
		FlushAll();
		CONDITIONAL_LOG_EXIT(targetAddr);
		WriteExit(targetAddr, js.nextExit++);
		break;

	default:
		_dbg_assert_msg_(CPU,0,"Trying to compile instruction that can't be compiled");
		break;
	}
	js.compiling = false;
}

static u32 savedPC;

void Jit::Comp_JumpReg(MIPSOpcode op)
{
	CONDITIONAL_LOG;
	if (js.inDelaySlot) {
		ERROR_LOG_REPORT(JIT, "Branch in JumpReg delay slot at %08x in block starting at %08x", js.compilerPC, js.blockStart);
		return;
	}
	MIPSGPReg rs = _RS;
	MIPSGPReg rd = _RD;
	bool andLink = (op & 0x3f) == 9;

	MIPSOpcode delaySlotOp = Memory::Read_Instruction(js.compilerPC + 4);
	bool delaySlotIsNice = IsDelaySlotNiceReg(op, delaySlotOp, rs);
	if (andLink && rs == rd)
		delaySlotIsNice = false;
	CONDITIONAL_NICE_DELAYSLOT;

	if (IsSyscall(delaySlotOp))
	{
		// If this is a syscall, write the pc (for thread switching and other good reasons.)
		gpr.MapReg(rs, true, false);
		MOV(32, M(&currentMIPS->pc), gpr.R(rs));
		if (andLink)
			gpr.SetImm(rd, js.compilerPC + 8);
		CompileDelaySlot(DELAYSLOT_FLUSH);

		// Syscalls write the exit code for us.
		_dbg_assert_msg_(JIT, !js.compiling, "Expected syscall to write an exit code.");
		return;
	}
	else if (delaySlotIsNice)
	{
		if (andLink)
			gpr.SetImm(rd, js.compilerPC + 8);
		CompileDelaySlot(DELAYSLOT_NICE);

		if (!andLink && rs == MIPS_REG_RA && g_Config.bDiscardRegsOnJRRA) {
			// According to the MIPS ABI, there are some regs we don't need to preserve.
			// Let's discard them so we don't need to write them back.
			// NOTE: Not all games follow the MIPS ABI! Tekken 6, for example, will crash
			// with this enabled.
			gpr.DiscardRegContentsIfCached(MIPS_REG_COMPILER_SCRATCH);
			for (int i = MIPS_REG_A0; i <= MIPS_REG_T7; i++)
				gpr.DiscardRegContentsIfCached((MIPSGPReg)i);
			gpr.DiscardRegContentsIfCached(MIPS_REG_T8);
			gpr.DiscardRegContentsIfCached(MIPS_REG_T9);
		}

		if (jo.continueJumps && gpr.IsImm(rs) && js.numInstructions < jo.continueMaxInstructions)
		{
			// Account for the increment in the loop.
			js.compilerPC = gpr.GetImm(rs) - 4;
			// In case the delay slot was a break or something.
			js.compiling = true;
			return;
		}

		MOV(32, R(EAX), gpr.R(rs));
		FlushAll();
	}
	else
	{
		// Latch destination now - save it in memory.
		gpr.MapReg(rs, true, false);
		MOV(32, M(&savedPC), gpr.R(rs));
		if (andLink)
			gpr.SetImm(rd, js.compilerPC + 8);
		CompileDelaySlot(DELAYSLOT_NICE);
		MOV(32, R(EAX), M(&savedPC));
		FlushAll();
	}

	switch (op & 0x3f)
	{
	case 8: //jr
		break;
	case 9: //jalr
		break;
	default:
		_dbg_assert_msg_(CPU,0,"Trying to compile instruction that can't be compiled");
		break;
	}

	CONDITIONAL_LOG_EXIT_EAX();
	WriteExitDestInEAX();
	js.compiling = false;
}

void Jit::Comp_Syscall(MIPSOpcode op)
{
	// TODO: Maybe discard v0, v1, and some temps?  Definitely at?
	FlushAll();

	// If we're in a delay slot, this is off by one.
	const int offset = js.inDelaySlot ? -1 : 0;
	WriteDowncount(offset);
	js.downcountAmount = -offset;

	// Skip the CallSyscall where possible.
	void *quickFunc = GetQuickSyscallFunc(op);
	if (quickFunc)
		ABI_CallFunctionP(quickFunc, (void *)GetSyscallInfo(op));
	else
		ABI_CallFunctionC((void *)&CallSyscall, op.encoding);

	WriteSyscallExit();
	js.compiling = false;
}

void Jit::Comp_Break(MIPSOpcode op)
{
	Comp_Generic(op);
	WriteSyscallExit();
	js.compiling = false;
}

}	 // namespace Mipscomp