void BlockState::init(DSEContext &Ctx, bool Optimistic) {
std::vector<LSLocation> &LV = Ctx.getLocationVault();
LocationNum = LV.size();
// For function that requires just 1 iteration of the data flow to converge
// we set the initial state of BBWriteSetIn to 0.
//
// For other functions, the initial state of BBWriteSetIn should be all 1's.
// Otherwise the dataflow solution could be too conservative.
//
// Consider this case, the dead store by var a = 10 before the loop will not
// be eliminated if the BBWriteSetIn is set to 0 initially.
//
// var a = 10
// for _ in 0...1024 {}
// a = 10
//
// However, by doing so, we can only eliminate the dead stores after the
// data flow stabilizes.
//
BBWriteSetIn.resize(LocationNum, Optimistic);
BBWriteSetOut.resize(LocationNum, false);
BBWriteSetMid.resize(LocationNum, false);
// GenSet and KillSet initially empty.
BBGenSet.resize(LocationNum, false);
BBKillSet.resize(LocationNum, false);
// MaxStoreSet is optimistically set to true initially.
BBMaxStoreSet.resize(LocationNum, true);
// DeallocateLocation initially empty.
BBDeallocateLocation.resize(LocationNum, false);
}
void BlockState::initStoreSetAtEndOfBlock(DSEContext &Ctx) {
std::vector<LSLocation> &LocationVault = Ctx.getLocationVault();
// We set the store bit at the end of the basic block in which a stack
// allocated location is deallocated.
for (unsigned i = 0; i < LocationVault.size(); ++i) {
// Turn on the store bit at the block which the stack slot is deallocated.
if (auto *ASI = dyn_cast<AllocStackInst>(LocationVault[i].getBase())) {
for (auto X : findDeallocStackInst(ASI)) {
SILBasicBlock *DSIBB = X->getParent();
if (DSIBB != BB)
continue;
startTrackingLocation(BBDeallocateLocation, i);
}
}
if (auto *ARI = dyn_cast<AllocRefInst>(LocationVault[i].getBase())) {
if (!ARI->isAllocatingStack())
continue;
for (auto X : findDeallocRefInst(ARI)) {
SILBasicBlock *DSIBB = X->getParent();
if (DSIBB != BB)
continue;
startTrackingLocation(BBDeallocateLocation, i);
}
}
}
}
