@@ -18,6 +18,7 @@ - Implemented BIOS routines SoftReset, RegisterRamReset, Diff8bitUnFilterWram, Diff8bitUnFilterVram, and Diff16bitUnFilter
  - Support IPv6
  - Save directory of last loaded file
  - Support BPS patches
+ - Automatically detect and optimize out idle loops
  - Configurable game overrides
  - Support loading 7-Zip files
  - Drag and drop game loading

@@ -212,6 +212,18 @@
 	_lookupIntValue(config, "fullscreen", &opts->fullscreen);
 	_lookupIntValue(config, "width", &opts->width);
 	_lookupIntValue(config, "height", &opts->height);
+
+	char* idleOptimization = 0;
+	if (_lookupCharValue(config, "idleOptimization", &idleOptimization)) {
+		if (strcasecmp(idleOptimization, "ignore") == 0) {
+			opts->idleOptimization = IDLE_LOOP_IGNORE;
+		} else if (strcasecmp(idleOptimization, "remove") == 0) {
+			opts->idleOptimization = IDLE_LOOP_REMOVE;
+		} else if (strcasecmp(idleOptimization, "detect") == 0) {
+			opts->idleOptimization = IDLE_LOOP_DETECT;
+		}
+		free(idleOptimization);
+	}
 }
 
 void GBAConfigLoadDefaults(struct GBAConfig* config, const struct GBAOptions* opts) {
@@ -231,6 +243,18 @@ ConfigurationSetIntValue(&config->defaultsTable, 0, "width", opts->width);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "height", opts->height);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "lockAspectRatio", opts->lockAspectRatio);
 	ConfigurationSetIntValue(&config->defaultsTable, 0, "resampleVideo", opts->resampleVideo);
+
+	switch (opts->idleOptimization) {
+	case IDLE_LOOP_IGNORE:
+		ConfigurationSetValue(&config->defaultsTable, 0, "idleOptimization", "ignore");
+		break;
+	case IDLE_LOOP_REMOVE:
+		ConfigurationSetValue(&config->defaultsTable, 0, "idleOptimization", "remove");
+		break;
+	case IDLE_LOOP_DETECT:
+		ConfigurationSetValue(&config->defaultsTable, 0, "idleOptimization", "detect");
+		break;
+	}
 }
 
 void GBAConfigFreeOpts(struct GBAOptions* opts) {

@@ -8,6 +8,8 @@ #define GBA_CONFIG_H
 
 #include "util/common.h"
 
+#include "gba.h"
+
 #include "util/configuration.h"
 
 struct GBAConfig {
@@ -35,6 +37,8 @@ bool resampleVideo;
 
 	bool videoSync;
 	bool audioSync;
+
+	enum GBAIdleLoopOptimization idleOptimization;
 };
 
 void GBAConfigInit(struct GBAConfig*, const char* port);

@@ -567,6 +567,7 @@ gba->memory.io[(address >> 1) + 1] = value >> 16;
 }
 
 uint16_t GBAIORead(struct GBA* gba, uint32_t address) {
+	gba->lastJump = -1; // IO reads need to invalidate detected idle loops
 	switch (address) {
 	case REG_TM0CNT_LO:
 		GBATimerUpdateRegister(gba, 0);

@@ -7,11 +7,14 @@ #include "gba-memory.h"
 
 #include "macros.h"
 
+#include "decoder.h"
 #include "gba-gpio.h"
 #include "gba-io.h"
 #include "gba-serialize.h"
 #include "hle-bios.h"
 #include "util/memory.h"
+
+#define IDLE_LOOP_THRESHOLD 10000
 
 static uint32_t _popcount32(unsigned bits);
 static uint32_t _deadbeef[2] = { 0xDEADBEEF, 0xFEEDFACE };
@@ -114,18 +117,118 @@ GBALog(gba, GBA_LOG_FATAL, "Could not map memory");
 	}
 }
 
+static void _analyzeForIdleLoop(struct GBA* gba, struct ARMCore* cpu, uint32_t address) {
+	struct ARMInstructionInfo info;
+	uint32_t nextAddress = address;
+	memset(gba->taintedRegisters, 0, sizeof(gba->taintedRegisters));
+	if (cpu->executionMode == MODE_THUMB) {
+		while (true) {
+			uint16_t opcode;
+			LOAD_16(opcode, nextAddress & cpu->memory.activeMask, cpu->memory.activeRegion);
+			ARMDecodeThumb(opcode, &info);
+			switch (info.branchType) {
+			case ARM_BRANCH_NONE:
+				if (info.operandFormat & ARM_OPERAND_MEMORY_2) {
+					if (info.mnemonic == ARM_MN_STR || gba->taintedRegisters[info.memory.baseReg]) {
+						gba->idleDetectionStep = -1;
+						return;
+					}
+					uint32_t loadAddress = gba->cachedRegisters[info.memory.baseReg];
+					uint32_t offset = 0;
+					if (info.memory.format & ARM_MEMORY_IMMEDIATE_OFFSET) {
+						offset = info.memory.offset.immediate;
+					} else if (info.memory.format & ARM_MEMORY_REGISTER_OFFSET) {
+						int reg = info.memory.offset.reg;
+						if (gba->cachedRegisters[reg]) {
+							gba->idleDetectionStep = -1;
+							return;
+						}
+						offset = gba->cachedRegisters[reg];
+					}
+					if (info.memory.format & ARM_MEMORY_OFFSET_SUBTRACT) {
+						loadAddress -= offset;
+					} else {
+						loadAddress += offset;
+					}
+					if ((loadAddress >> BASE_OFFSET) == REGION_IO) {
+						gba->idleDetectionStep = -1;
+						return;
+					}
+					if ((loadAddress >> BASE_OFFSET) < REGION_CART0 || (loadAddress >> BASE_OFFSET) > REGION_CART2_EX) {
+						gba->taintedRegisters[info.op1.reg] = true;
+					} else {
+						switch (info.memory.width) {
+						case 1:
+							gba->cachedRegisters[info.op1.reg] = GBALoad8(cpu, loadAddress, 0);
+							break;
+						case 2:
+							gba->cachedRegisters[info.op1.reg] = GBALoad16(cpu, loadAddress, 0);
+							break;
+						case 4:
+							gba->cachedRegisters[info.op1.reg] = GBALoad32(cpu, loadAddress, 0);
+							break;
+						}
+					}
+				} else if (info.operandFormat & ARM_OPERAND_AFFECTED_1) {
+					gba->taintedRegisters[info.op1.reg] = true;
+				}
+				nextAddress += WORD_SIZE_THUMB;
+				break;
+			case ARM_BRANCH:
+				if ((uint32_t) info.op1.immediate + nextAddress + WORD_SIZE_THUMB * 2 == address) {
+					gba->idleLoop = address;
+					gba->idleOptimization = IDLE_LOOP_REMOVE;
+				}
+				gba->idleDetectionStep = -1;
+				return;
+			default:
+				gba->idleDetectionStep = -1;
+				return;
+			}
+		}
+	} else {
+		gba->idleDetectionStep = -1;
+	}
+}
+
 static void GBASetActiveRegion(struct ARMCore* cpu, uint32_t address) {
 	struct GBA* gba = (struct GBA*) cpu->master;
 	struct GBAMemory* memory = &gba->memory;
 
-	if (address == gba->busyLoop && memory->activeRegion != REGION_BIOS) {
-		GBAHalt(gba);
+	int newRegion = address >> BASE_OFFSET;
+	if (gba->idleOptimization >= IDLE_LOOP_REMOVE && memory->activeRegion != REGION_BIOS) {
+		if (address == gba->lastJump && address == gba->idleLoop) {
+			GBAHalt(gba);
+		} else if (gba->idleOptimization >= IDLE_LOOP_DETECT && newRegion == memory->activeRegion) {
+			if (address == gba->lastJump) {
+				switch (gba->idleDetectionStep) {
+				case 0:
+					memcpy(gba->cachedRegisters, cpu->gprs, sizeof(gba->cachedRegisters));
+					++gba->idleDetectionStep;
+					break;
+				case 1:
+					if (memcmp(gba->cachedRegisters, cpu->gprs, sizeof(gba->cachedRegisters))) {
+						gba->idleDetectionStep = -1;
+						++gba->idleDetectionFailures;
+						if (gba->idleDetectionFailures > IDLE_LOOP_THRESHOLD) {
+							gba->idleOptimization = IDLE_LOOP_IGNORE;
+						}
+						break;
+					}
+					_analyzeForIdleLoop(gba, cpu, address);
+					break;
+				}
+			} else {
+				gba->idleDetectionStep = 0;
+			}
+		}
 	}
 
-	int newRegion = address >> BASE_OFFSET;
+	gba->lastJump = address;
 	if (newRegion == memory->activeRegion) {
 		return;
 	}
+
 	if (memory->activeRegion == REGION_BIOS) {
 		memory->biosPrefetch = cpu->prefetch[1];
 	}

@@ -26,7 +26,7 @@ { "V49J", SAVEDATA_SRAM, GPIO_RUMBLE, -1 },
 	{ "V49E", SAVEDATA_SRAM, GPIO_RUMBLE, -1 },
 
 	// Final Fantasy Tactics Advance
-	{ "AFXE", SAVEDATA_FLASH512, GPIO_NONE, 0x8000418 },
+	{ "AFXE", SAVEDATA_FLASH512, GPIO_NONE, 0x8000428 },
 
 	// Koro Koro Puzzle - Happy Panechu!
 	{ "KHPJ", SAVEDATA_EEPROM, GPIO_TILT, -1 },
@@ -240,6 +240,9 @@ }
 	}
 
 	if (override->idleLoop != 0xFFFFFFFF) {
-		gba->busyLoop = override->idleLoop;
+		gba->idleLoop = override->idleLoop;
+		if (gba->idleOptimization == IDLE_LOOP_DETECT) {
+			gba->idleOptimization = IDLE_LOOP_REMOVE;
+		}
 	}
 }

@@ -120,6 +120,7 @@ ARMInit(&cpu);
 	gba.sync = &threadContext->sync;
 	threadContext->gba = &gba;
 	gba.logLevel = threadContext->logLevel;
+	gba.idleOptimization = threadContext->idleOptimization;
 #ifdef USE_PTHREADS
 	pthread_setspecific(_contextKey, threadContext);
 #else
@@ -260,6 +261,8 @@
 	if (opts->audioBuffers) {
 		threadContext->audioBuffers = opts->audioBuffers;
 	}
+
+	threadContext->idleOptimization = opts->idleOptimization;
 }
 
 void GBAMapArgumentsToContext(const struct GBAArguments* args, struct GBAThread* threadContext) {

@@ -72,6 +72,7 @@ const char* fname;
 	int activeKeys;
 	struct GBAAVStream* stream;
 	struct Configuration* overrides;
+	enum GBAIdleLoopOptimization idleOptimization;
 
 	bool hasOverride;
 	struct GBACartridgeOverride override;

@@ -76,7 +76,11 @@ gba->logLevel = GBA_LOG_INFO | GBA_LOG_WARN | GBA_LOG_ERROR | GBA_LOG_FATAL;
 
 	gba->biosChecksum = GBAChecksum(gba->memory.bios, SIZE_BIOS);
 
-	gba->busyLoop = -1;
+	gba->idleOptimization = IDLE_LOOP_REMOVE;
+	gba->idleLoop = -1;
+	gba->lastJump = 0;
+	gba->idleDetectionStep = 0;
+	gba->idleDetectionFailures = 0;
 	gba->performingDMA = false;
 }
 

@@ -75,6 +75,12 @@ GBA_COMPONENT_DEBUGGER,
 	GBA_COMPONENT_MAX
 };
 
+enum GBAIdleLoopOptimization {
+	IDLE_LOOP_IGNORE = -1,
+	IDLE_LOOP_REMOVE = 0,
+	IDLE_LOOP_DETECT
+};
+
 enum {
 	SP_BASE_SYSTEM = 0x03007F00,
 	SP_BASE_IRQ = 0x03007FA0,
@@ -120,7 +126,6 @@
 	int springIRQ;
 	uint32_t biosChecksum;
 	int* keySource;
-	uint32_t busyLoop;
 	struct GBARotationSource* rotationSource;
 	struct GBALuminanceSource* luminanceSource;
 	struct GBARTCSource* rtcSource;
@@ -136,6 +141,14 @@
 	const char* activeFile;
 
 	int logLevel;
+
+	enum GBAIdleLoopOptimization idleOptimization;
+	uint32_t idleLoop;
+	uint32_t lastJump;
+	int idleDetectionStep;
+	int idleDetectionFailures;
+	int32_t cachedRegisters[16];
+	bool taintedRegisters[16];
 };
 
 struct GBACartridge {

@@ -56,7 +56,11 @@ struct GBAConfig config;
 	GBAConfigInit(&config, "perf");
 	GBAConfigLoad(&config);
 
-	struct GBAOptions opts = {};
+	struct GBAOptions opts = {
+		.idleOptimization = IDLE_LOOP_DETECT
+	};
+	GBAConfigLoadDefaults(&config, &opts);
+
 	struct GBAArguments args = {};
 	if (!parseArguments(&args, &config, argc, argv, &subparser)) {
 		usage(argv[0], PERF_USAGE);
@@ -69,7 +73,7 @@
 	renderer.outputBuffer = malloc(256 * 256 * 4);
 	renderer.outputBufferStride = 256;
 
-	struct GBAThread context = { };
+	struct GBAThread context = {};
 	_thread = &context;
 
 	if (!perfOpts.noVideo) {