/*
* Perform a pass of top-down walk to
* 1) Eliminate redundant loads and stores
* 2) Sink stores to latest possible slot
*/
static void applyLoadStoreElimination(CompilationUnit *cUnit,
ArmLIR *headLIR,
ArmLIR *tailLIR)
{
ArmLIR *thisLIR;
cUnit->optRound++;
for (thisLIR = headLIR;
thisLIR != tailLIR;
thisLIR = NEXT_LIR(thisLIR)) {
/* Skip newly added instructions */
if (thisLIR->age >= cUnit->optRound) {
continue;
}
if (isDalvikStore(thisLIR)) {
int dRegId = DECODE_ALIAS_INFO_REG(thisLIR->aliasInfo);
int dRegIdHi = dRegId + DECODE_ALIAS_INFO_WIDE(thisLIR->aliasInfo);
int nativeRegId = thisLIR->operands[0];
ArmLIR *checkLIR;
int sinkDistance = 0;
/*
* Add r15 (pc) to the mask to prevent this instruction
* from sinking past branch instructions. Unset the Dalvik register
* bit when checking with native resource constraints.
*/
u8 stopMask = (ENCODE_REG_PC | thisLIR->useMask) &
~ENCODE_DALVIK_REG;
for (checkLIR = NEXT_LIR(thisLIR);
checkLIR != tailLIR;
checkLIR = NEXT_LIR(checkLIR)) {
/* Check if a Dalvik register load is redundant */
if (isDalvikLoad(checkLIR) &&
(checkLIR->aliasInfo == thisLIR->aliasInfo) &&
(REGTYPE(checkLIR->operands[0]) == REGTYPE(nativeRegId))) {
/* Insert a move to replace the load */
if (checkLIR->operands[0] != nativeRegId) {
ArmLIR *moveLIR;
moveLIR = dvmCompilerRegCopyNoInsert(
cUnit, checkLIR->operands[0], nativeRegId);
/*
* Insert the converted checkLIR instruction after the
* the original checkLIR since the optimization is
* scannng in the top-down order and the new instruction
* will need to be checked.
*/
dvmCompilerInsertLIRAfter((LIR *) checkLIR,
(LIR *) moveLIR);
}
checkLIR->isNop = true;
continue;
/*
* Found a true output dependency - nuke the previous store.
* The register type doesn't matter here.
*/
} else if (isDalvikStore(checkLIR) &&
(checkLIR->aliasInfo == thisLIR->aliasInfo)) {
thisLIR->isNop = true;
break;
/* Find out the latest slot that the store can be sunk into */
} else {
/* Last instruction reached */
bool stopHere = (NEXT_LIR(checkLIR) == tailLIR);
/* Store data is clobbered */
stopHere |= ((stopMask & checkLIR->defMask) != 0);
/* Store data partially clobbers the Dalvik register */
if (stopHere == false &&
((checkLIR->useMask | checkLIR->defMask) &
ENCODE_DALVIK_REG)) {
stopHere = isDalvikRegisterClobbered(thisLIR, checkLIR);
}
/* Found a new place to put the store - move it here */
if (stopHere == true) {
DEBUG_OPT(dumpDependentInsnPair(thisLIR, checkLIR,
"SINK STORE"));
/* The store can be sunk for at least one cycle */
if (sinkDistance != 0) {
ArmLIR *newStoreLIR =
dvmCompilerNew(sizeof(ArmLIR), true);
*newStoreLIR = *thisLIR;
newStoreLIR->age = cUnit->optRound;
/*
* Stop point found - insert *before* the checkLIR
* since the instruction list is scanned in the
* top-down order.
*/
dvmCompilerInsertLIRBefore((LIR *) checkLIR,
(LIR *) newStoreLIR);
thisLIR->isNop = true;
}
break;
}
/*
* Saw a real instruction that the store can be sunk after
*/
if (!isPseudoOpCode(checkLIR->opCode)) {
sinkDistance++;
}
}
}
}
}
}
/*
* Perform a pass of top-down walk, from the second-last instruction in the
* superblock, to eliminate redundant loads and stores.
*
* An earlier load can eliminate a later load iff
* 1) They are must-aliases
* 2) The native register is not clobbered in between
* 3) The memory location is not written to in between
*
* An earlier store can eliminate a later load iff
* 1) They are must-aliases
* 2) The native register is not clobbered in between
* 3) The memory location is not written to in between
*
* A later store can be eliminated by an earlier store iff
* 1) They are must-aliases
* 2) The memory location is not written to in between
*/
static void applyLoadStoreElimination(CompilationUnit *cUnit,
MipsLIR *headLIR,
MipsLIR *tailLIR)
{
MipsLIR *thisLIR;
if (headLIR == tailLIR) return;
for (thisLIR = PREV_LIR(tailLIR);
thisLIR != headLIR;
thisLIR = PREV_LIR(thisLIR)) {
int sinkDistance = 0;
/* Skip non-interesting instructions */
if ((thisLIR->flags.isNop == true) ||
isPseudoOpCode(thisLIR->opcode) ||
!(EncodingMap[thisLIR->opcode].flags & (IS_LOAD | IS_STORE))) {
continue;
}
int nativeRegId = thisLIR->operands[0];
bool isThisLIRLoad = EncodingMap[thisLIR->opcode].flags & IS_LOAD;
MipsLIR *checkLIR;
/* Use the mem mask to determine the rough memory location */
u8 thisMemMask = (thisLIR->useMask | thisLIR->defMask) & ENCODE_MEM;
/*
* Currently only eliminate redundant ld/st for constant and Dalvik
* register accesses.
*/
if (!(thisMemMask & (ENCODE_LITERAL | ENCODE_DALVIK_REG))) continue;
/*
* Add r15 (pc) to the resource mask to prevent this instruction
* from sinking past branch instructions. Also take out the memory
* region bits since stopMask is used to check data/control
* dependencies.
*/
u8 stopUseRegMask = (ENCODE_REG_PC | thisLIR->useMask) &
~ENCODE_MEM;
u8 stopDefRegMask = thisLIR->defMask & ~ENCODE_MEM;
for (checkLIR = NEXT_LIR(thisLIR);
checkLIR != tailLIR;
checkLIR = NEXT_LIR(checkLIR)) {
/*
* Skip already dead instructions (whose dataflow information is
* outdated and misleading).
*/
if (checkLIR->flags.isNop) continue;
u8 checkMemMask = (checkLIR->useMask | checkLIR->defMask) &
ENCODE_MEM;
u8 aliasCondition = thisMemMask & checkMemMask;
bool stopHere = false;
/*
* Potential aliases seen - check the alias relations
*/
if (checkMemMask != ENCODE_MEM && aliasCondition != 0) {
bool isCheckLIRLoad = EncodingMap[checkLIR->opcode].flags &
IS_LOAD;
if (aliasCondition == ENCODE_LITERAL) {
/*
* Should only see literal loads in the instruction
* stream.
*/
assert(!(EncodingMap[checkLIR->opcode].flags &
IS_STORE));
/* Same value && same register type */
if (checkLIR->aliasInfo == thisLIR->aliasInfo &&
REGTYPE(checkLIR->operands[0]) == REGTYPE(nativeRegId)){
/*
* Different destination register - insert
* a move
*/
if (checkLIR->operands[0] != nativeRegId) {
convertMemOpIntoMove(cUnit, checkLIR,
checkLIR->operands[0],
nativeRegId);
}
checkLIR->flags.isNop = true;
}
} else if (aliasCondition == ENCODE_DALVIK_REG) {
/* Must alias */
if (checkLIR->aliasInfo == thisLIR->aliasInfo) {
/* Only optimize compatible registers */
bool regCompatible =
REGTYPE(checkLIR->operands[0]) ==
REGTYPE(nativeRegId);
if ((isThisLIRLoad && isCheckLIRLoad) ||
(!isThisLIRLoad && isCheckLIRLoad)) {
/* RAR or RAW */
if (regCompatible) {
/*
* Different destination register -
* insert a move
*/
if (checkLIR->operands[0] !=
nativeRegId) {
convertMemOpIntoMove(cUnit,
checkLIR,
checkLIR->operands[0],
nativeRegId);
}
checkLIR->flags.isNop = true;
} else {
/*
* Destinaions are of different types -
* something complicated going on so
* stop looking now.
*/
stopHere = true;
}
} else if (isThisLIRLoad && !isCheckLIRLoad) {
/* WAR - register value is killed */
stopHere = true;
} else if (!isThisLIRLoad && !isCheckLIRLoad) {
/* WAW - nuke the earlier store */
thisLIR->flags.isNop = true;
stopHere = true;
}
/* Partial overlap */
} else if (isDalvikRegisterClobbered(thisLIR, checkLIR)) {
/*
* It is actually ok to continue if checkLIR
* is a read. But it is hard to make a test
* case for this so we just stop here to be
* conservative.
*/
stopHere = true;
}
}
/* Memory content may be updated. Stop looking now. */
if (stopHere) {
break;
/* The checkLIR has been transformed - check the next one */
} else if (checkLIR->flags.isNop) {
continue;
}
}
/*
* this and check LIRs have no memory dependency. Now check if
* their register operands have any RAW, WAR, and WAW
* dependencies. If so, stop looking.
*/
if (stopHere == false) {
stopHere = CHECK_REG_DEP(stopUseRegMask, stopDefRegMask,
checkLIR);
}
if (stopHere == true) {
DEBUG_OPT(dumpDependentInsnPair(thisLIR, checkLIR,
"REG CLOBBERED"));
/* Only sink store instructions */
if (sinkDistance && !isThisLIRLoad) {
MipsLIR *newStoreLIR =
(MipsLIR *) dvmCompilerNew(sizeof(MipsLIR), true);
*newStoreLIR = *thisLIR;
/*
* Stop point found - insert *before* the checkLIR
* since the instruction list is scanned in the
* top-down order.
*/
dvmCompilerInsertLIRBefore((LIR *) checkLIR,
(LIR *) newStoreLIR);
thisLIR->flags.isNop = true;
}
break;
} else if (!checkLIR->flags.isNop) {
sinkDistance++;
}
}
}
}
static void applyLoadHoisting(CompilationUnit *cUnit,
ArmLIR *headLIR,
ArmLIR *tailLIR)
{
ArmLIR *thisLIR;
/*
* Don't want to hoist in front of first load following a barrier (or
* first instruction of the block.
*/
bool firstLoad = true;
int maxHoist = dvmCompilerTargetOptHint(kMaxHoistDistance);
cUnit->optRound++;
for (thisLIR = headLIR;
thisLIR != tailLIR;
thisLIR = NEXT_LIR(thisLIR)) {
/* Skip newly added instructions */
if (thisLIR->age >= cUnit->optRound ||
thisLIR->isNop == true) {
continue;
}
if (firstLoad && (EncodingMap[thisLIR->opCode].flags & IS_LOAD)) {
/*
* Ensure nothing will be hoisted in front of this load because
* it's result will likely be needed soon.
*/
thisLIR->defMask |= ENCODE_MEM_USE;
firstLoad = false;
}
firstLoad |= (thisLIR->defMask == ENCODE_ALL);
if (isDalvikLoad(thisLIR)) {
int dRegId = DECODE_ALIAS_INFO_REG(thisLIR->aliasInfo);
int dRegIdHi = dRegId + DECODE_ALIAS_INFO_WIDE(thisLIR->aliasInfo);
int nativeRegId = thisLIR->operands[0];
ArmLIR *checkLIR;
int hoistDistance = 0;
u8 stopUseMask = (ENCODE_REG_PC | thisLIR->useMask);
u8 stopDefMask = thisLIR->defMask;
u8 checkResult;
/* First check if the load can be completely elinimated */
for (checkLIR = PREV_LIR(thisLIR);
checkLIR != headLIR;
checkLIR = PREV_LIR(checkLIR)) {
if (checkLIR->isNop) continue;
/*
* Check if the Dalvik register is previously accessed
* with exactly the same type.
*/
if ((isDalvikLoad(checkLIR) || isDalvikStore(checkLIR)) &&
(checkLIR->aliasInfo == thisLIR->aliasInfo) &&
(checkLIR->operands[0] == nativeRegId)) {
/*
* If it is previously accessed but with a different type,
* the search will terminate later at the point checking
* for partially overlapping stores.
*/
thisLIR->isNop = true;
break;
}
/*
* No earlier use/def can reach this load if:
* 1) Head instruction is reached
*/
if (checkLIR == headLIR) {
break;
}
checkResult = (stopUseMask | stopDefMask) & checkLIR->defMask;
/*
* If both instructions are verified Dalvik accesses, clear the
* may- and must-alias bits to detect true resource
* dependencies.
*/
if (checkResult & ENCODE_DALVIK_REG) {
checkResult &= ~(ENCODE_DALVIK_REG | ENCODE_FRAME_REF);
}
/*
* 2) load target register is clobbered
* 3) A branch is seen (stopUseMask has the PC bit set).
*/
if (checkResult) {
break;
}
/* Store data partially clobbers the Dalvik register */
if (isDalvikStore(checkLIR) &&
isDalvikRegisterClobbered(thisLIR, checkLIR)) {
break;
}
}
/* The load has been eliminated */
if (thisLIR->isNop) continue;
/*
* The load cannot be eliminated. See if it can be hoisted to an
* earlier spot.
*/
for (checkLIR = PREV_LIR(thisLIR);
/* empty by intention */;
checkLIR = PREV_LIR(checkLIR)) {
if (checkLIR->isNop) continue;
/*
* Check if the "thisLIR" load is redundant
* NOTE: At one point, we also triggered if the checkLIR
* instruction was a load. However, that tended to insert
* a load/use dependency because the full scheduler is
* not yet complete. When it is, we chould also trigger
* on loads.
*/
if (isDalvikStore(checkLIR) &&
(checkLIR->aliasInfo == thisLIR->aliasInfo) &&
(REGTYPE(checkLIR->operands[0]) == REGTYPE(nativeRegId))) {
/* Insert a move to replace the load */
if (checkLIR->operands[0] != nativeRegId) {
ArmLIR *moveLIR;
moveLIR = dvmCompilerRegCopyNoInsert(
cUnit, nativeRegId, checkLIR->operands[0]);
/*
* Convert *thisLIR* load into a move
*/
dvmCompilerInsertLIRAfter((LIR *) checkLIR,
(LIR *) moveLIR);
}
thisLIR->isNop = true;
break;
/* Find out if the load can be yanked past the checkLIR */
} else {
/* Last instruction reached */
bool stopHere = (checkLIR == headLIR);
/* Base address is clobbered by checkLIR */
checkResult = stopUseMask & checkLIR->defMask;
if (checkResult & ENCODE_DALVIK_REG) {
checkResult &= ~(ENCODE_DALVIK_REG | ENCODE_FRAME_REF);
}
stopHere |= (checkResult != 0);
/* Load target clobbers use/def in checkLIR */
checkResult = stopDefMask &
(checkLIR->useMask | checkLIR->defMask);
if (checkResult & ENCODE_DALVIK_REG) {
checkResult &= ~(ENCODE_DALVIK_REG | ENCODE_FRAME_REF);
}
stopHere |= (checkResult != 0);
/* Store data partially clobbers the Dalvik register */
if (stopHere == false &&
(checkLIR->defMask & ENCODE_DALVIK_REG)) {
stopHere = isDalvikRegisterClobbered(thisLIR, checkLIR);
}
/*
* Stop at an earlier Dalvik load if the offset of checkLIR
* is not less than thisLIR
*
* Experiments show that doing
*
* ldr r1, [r5, #16]
* ldr r0, [r5, #20]
*
* is much faster than
*
* ldr r0, [r5, #20]
* ldr r1, [r5, #16]
*/
if (isDalvikLoad(checkLIR)) {
int dRegId2 =
DECODE_ALIAS_INFO_REG(checkLIR->aliasInfo);
if (dRegId2 <= dRegId) {
stopHere = true;
}
}
/* Don't go too far */
stopHere |= (hoistDistance >= maxHoist);
/* Found a new place to put the load - move it here */
if (stopHere == true) {
DEBUG_OPT(dumpDependentInsnPair(thisLIR, checkLIR,
"HOIST LOAD"));
/* The load can be hoisted for at least one cycle */
if (hoistDistance != 0) {
ArmLIR *newLoadLIR =
dvmCompilerNew(sizeof(ArmLIR), true);
*newLoadLIR = *thisLIR;
newLoadLIR->age = cUnit->optRound;
/*
* Stop point found - insert *after* the checkLIR
* since the instruction list is scanned in the
* bottom-up order.
*/
dvmCompilerInsertLIRAfter((LIR *) checkLIR,
(LIR *) newLoadLIR);
thisLIR->isNop = true;
}
break;
}
/*
* Saw a real instruction that hosting the load is
* beneficial
*/
if (!isPseudoOpCode(checkLIR->opCode)) {
hoistDistance++;
}
}
}
} else if (isLiteralLoad(thisLIR)) {
int litVal = thisLIR->aliasInfo;
int nativeRegId = thisLIR->operands[0];
ArmLIR *checkLIR;
int hoistDistance = 0;
u8 stopUseMask = (ENCODE_REG_PC | thisLIR->useMask) &
~ENCODE_LITPOOL_REF;
u8 stopDefMask = thisLIR->defMask & ~ENCODE_LITPOOL_REF;
/* First check if the load can be completely elinimated */
for (checkLIR = PREV_LIR(thisLIR);
checkLIR != headLIR;
checkLIR = PREV_LIR(checkLIR)) {
if (checkLIR->isNop) continue;
/* Reloading same literal into same tgt reg? Eliminate if so */
if (isLiteralLoad(checkLIR) &&
(checkLIR->aliasInfo == litVal) &&
(checkLIR->operands[0] == nativeRegId)) {
thisLIR->isNop = true;
break;
}
/*
* No earlier use/def can reach this load if:
* 1) Head instruction is reached
* 2) load target register is clobbered
* 3) A branch is seen (stopUseMask has the PC bit set).
*/
if ((checkLIR == headLIR) ||
(stopUseMask | stopDefMask) & checkLIR->defMask) {
break;
}
}
/* The load has been eliminated */
if (thisLIR->isNop) continue;
/*
* The load cannot be eliminated. See if it can be hoisted to an
* earlier spot.
*/
for (checkLIR = PREV_LIR(thisLIR);
/* empty by intention */;
checkLIR = PREV_LIR(checkLIR)) {
if (checkLIR->isNop) continue;
/*
* TUNING: once a full scheduler exists, check here
* for conversion of a redundant load into a copy similar
* to the way redundant loads are handled above.
*/
/* Find out if the load can be yanked past the checkLIR */
/* Last instruction reached */
bool stopHere = (checkLIR == headLIR);
/* Base address is clobbered by checkLIR */
stopHere |= ((stopUseMask & checkLIR->defMask) != 0);
/* Load target clobbers use/def in checkLIR */
stopHere |= ((stopDefMask &
(checkLIR->useMask | checkLIR->defMask)) != 0);
/* Avoid re-ordering literal pool loads */
stopHere |= isLiteralLoad(checkLIR);
/* Don't go too far */
stopHere |= (hoistDistance >= maxHoist);
/* Found a new place to put the load - move it here */
if (stopHere == true) {
DEBUG_OPT(dumpDependentInsnPair(thisLIR, checkLIR,
"HOIST LOAD"));
/* The store can be hoisted for at least one cycle */
if (hoistDistance != 0) {
ArmLIR *newLoadLIR =
dvmCompilerNew(sizeof(ArmLIR), true);
*newLoadLIR = *thisLIR;
newLoadLIR->age = cUnit->optRound;
/*
* Insertion is guaranteed to succeed since checkLIR
* is never the first LIR on the list
*/
dvmCompilerInsertLIRAfter((LIR *) checkLIR,
(LIR *) newLoadLIR);
thisLIR->isNop = true;
}
break;
}
/*
* Saw a real instruction that hosting the load is
* beneficial
*/
if (!isPseudoOpCode(checkLIR->opCode)) {
hoistDistance++;
}
}
}
}
}