static bool
constantFoldStringConcatenation(ApplyInst *AI,
llvm::SetVector<SILInstruction *> &WorkList) {
SILBuilder B(AI);
// Try to apply the string literal concatenation optimization.
auto *Concatenated = tryToConcatenateStrings(AI, B);
// Bail if string literal concatenation could not be performed.
if (!Concatenated)
return false;
// Replace all uses of the old instruction by a new instruction.
AI->replaceAllUsesWith(Concatenated);
auto RemoveCallback = [&](SILInstruction *DeadI) { WorkList.remove(DeadI); };
// Remove operands that are not used anymore.
// Even if they are apply_inst, it is safe to
// do so, because they can only be applies
// of functions annotated as string.utf16
// or string.utf16.
for (auto &Op : AI->getAllOperands()) {
SILValue Val = Op.get();
Op.drop();
if (Val->use_empty()) {
auto *DeadI = dyn_cast<SILInstruction>(Val);
recursivelyDeleteTriviallyDeadInstructions(DeadI, /*force*/ true,
RemoveCallback);
WorkList.remove(DeadI);
}
}
// Schedule users of the new instruction for constant folding.
// We only need to schedule the string.concat invocations.
for (auto AIUse : Concatenated->getUses()) {
if (isApplyOfStringConcat(*AIUse->getUser())) {
WorkList.insert(AIUse->getUser());
}
}
// Delete the old apply instruction.
recursivelyDeleteTriviallyDeadInstructions(AI, /*force*/ true,
RemoveCallback);
return true;
}
