/// PropagateConstantsIntoArguments - Look at all uses of the specified
/// function. If all uses are direct call sites, and all pass a particular
/// constant in for an argument, propagate that constant in as the argument.
///
bool IPCP::PropagateConstantsIntoArguments(Function &F) {
if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.
// For each argument, keep track of its constant value and whether it is a
// constant or not. The bool is driven to true when found to be non-constant.
SmallVector<std::pair<Constant*, bool>, 16> ArgumentConstants;
ArgumentConstants.resize(F.arg_size());
unsigned NumNonconstant = 0;
for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
User *U = *UI;
// Ignore blockaddress uses.
if (isa<BlockAddress>(U)) continue;
// Used by a non-instruction, or not the callee of a function, do not
// transform.
if (!isa<CallInst>(U) && !isa<InvokeInst>(U))
return false;
CallSite CS(cast<Instruction>(U));
if (!CS.isCallee(UI))
return false;
// Check out all of the potentially constant arguments. Note that we don't
// inspect varargs here.
CallSite::arg_iterator AI = CS.arg_begin();
Function::arg_iterator Arg = F.arg_begin();
for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
++i, ++AI, ++Arg) {
// If this argument is known non-constant, ignore it.
if (ArgumentConstants[i].second)
continue;
Constant *C = dyn_cast<Constant>(*AI);
if (C && ArgumentConstants[i].first == 0) {
ArgumentConstants[i].first = C; // First constant seen.
} else if (C && ArgumentConstants[i].first == C) {
// Still the constant value we think it is.
} else if (*AI == &*Arg) {
// Ignore recursive calls passing argument down.
} else {
// Argument became non-constant. If all arguments are non-constant now,
// give up on this function.
if (++NumNonconstant == ArgumentConstants.size())
return false;
ArgumentConstants[i].second = true;
}
}
}
// If we got to this point, there is a constant argument!
assert(NumNonconstant != ArgumentConstants.size());
bool MadeChange = false;
Function::arg_iterator AI = F.arg_begin();
for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
// Do we have a constant argument?
if (ArgumentConstants[i].second || AI->use_empty() ||
AI->hasInAllocaAttr() || (AI->hasByValAttr() && !F.onlyReadsMemory()))
continue;
Value *V = ArgumentConstants[i].first;
if (V == 0) V = UndefValue::get(AI->getType());
AI->replaceAllUsesWith(V);
++NumArgumentsProped;
MadeChange = true;
}
return MadeChange;
}
