bool expandAtomicRMWToLLSC(AtomicRMWInst *AI);
bool expandAtomicRMWToCmpXchg(AtomicRMWInst *AI);
bool expandAtomicCmpXchg(AtomicCmpXchgInst *CI);
+ bool isIdempotentRMW(AtomicRMWInst *AI);
+ bool simplifyIdempotentRMW(AtomicRMWInst *AI);
};
}
MadeChange |= expandAtomicLoad(LI);
} else if (SI && TargetLowering->shouldExpandAtomicStoreInIR(SI)) {
MadeChange |= expandAtomicStore(SI);
- } else if (RMWI && TargetLowering->shouldExpandAtomicRMWInIR(RMWI)) {
- MadeChange |= expandAtomicRMW(RMWI);
+ } else if (RMWI) {
+ // There are two different ways of expanding RMW instructions:
+ // - into a load if it is idempotent
+ // - into a Cmpxchg/LL-SC loop otherwise
+ // we try them in that order.
+ MadeChange |= (isIdempotentRMW(RMWI) &&
+ simplifyIdempotentRMW(RMWI)) ||
+ (TargetLowering->shouldExpandAtomicRMWInIR(RMWI) &&
+ expandAtomicRMW(RMWI));
} else if (CASI && TargetLowering->hasLoadLinkedStoreConditional()) {
MadeChange |= expandAtomicCmpXchg(CASI);
}
CI->eraseFromParent();
return true;
}
+
+bool AtomicExpand::isIdempotentRMW(AtomicRMWInst* RMWI) {
+ auto C = dyn_cast<ConstantInt>(RMWI->getValOperand());
+ if(!C)
+ return false;
+
+ AtomicRMWInst::BinOp Op = RMWI->getOperation();
+ switch(Op) {
+ case AtomicRMWInst::Add:
+ case AtomicRMWInst::Sub:
+ case AtomicRMWInst::Or:
+ case AtomicRMWInst::Xor:
+ return C->isZero();
+ case AtomicRMWInst::And:
+ return C->isMinusOne();
+ // FIXME: we could also treat Min/Max/UMin/UMax by the INT_MIN/INT_MAX/...
+ default:
+ return false;
+ }
+}
+
+bool AtomicExpand::simplifyIdempotentRMW(AtomicRMWInst* RMWI) {
+ auto TLI = TM->getSubtargetImpl()->getTargetLowering();
+
+ if (auto ResultingLoad = TLI->lowerIdempotentRMWIntoFencedLoad(RMWI)) {
+ if (TLI->shouldExpandAtomicLoadInIR(ResultingLoad))
+ expandAtomicLoad(ResultingLoad);
+ return true;
+ }
+
+ return false;
+}