void rewriteFunctionType(IrFuncTy &fty) override {
const bool externD = (fty.type->linkage == LINKd &&
fty.type->parameterList.varargs != VARARGvariadic);
// return value:
if (!fty.ret->byref) {
Type *rt = fty.type->next->toBasetype(); // for sret, rt == void
if (isAggregate(rt) && !isMagicCppStruct(rt) && canRewriteAsInt(rt) &&
// don't rewrite cfloat for extern(D)
!(externD && rt->ty == Tcomplex32)) {
integerRewrite.applyToIfNotObsolete(*fty.ret);
}
}
// extern(D): try passing an argument in EAX
if (externD) {
// try an implicit argument...
if (fty.arg_this) {
Logger::println("Putting 'this' in register");
fty.arg_this->attrs.addAttribute(LLAttribute::InReg);
} else if (fty.arg_nest) {
Logger::println("Putting context ptr in register");
fty.arg_nest->attrs.addAttribute(LLAttribute::InReg);
} else if (IrFuncTyArg *sret = fty.arg_sret) {
Logger::println("Putting sret ptr in register");
// sret and inreg are incompatible, but the ABI requires the
// sret parameter to be in EAX in this situation...
sret->attrs.removeAttribute(LLAttribute::StructRet);
sret->attrs.addAttribute(LLAttribute::InReg);
}
// ... otherwise try the last argument
else if (!fty.args.empty()) {
// The last parameter is passed in EAX rather than being pushed on the
// stack if the following conditions are met:
// * It fits in EAX.
// * It is not a 3 byte struct.
// * It is not a floating point type.
IrFuncTyArg *last = fty.args.back();
Type *lastTy = last->type->toBasetype();
unsigned sz = lastTy->size();
if (last->byref && !last->isByVal()) {
Logger::println("Putting last (byref) parameter in register");
last->attrs.addAttribute(LLAttribute::InReg);
} else if (!lastTy->isfloating() && (sz == 1 || sz == 2 || sz == 4)) {
// rewrite aggregates as integers to make inreg work
if (lastTy->ty == Tstruct || lastTy->ty == Tsarray) {
integerRewrite.applyTo(*last);
// undo byval semantics applied via passByVal() returning true
last->byref = false;
last->attrs.clear();
}
last->attrs.addAttribute(LLAttribute::InReg);
}
}
// all other arguments are passed on the stack, don't rewrite
}
// extern(C++) on Posix: non-POD args are passed indirectly by-value
else if (!isMSVC && fty.type->linkage == LINKcpp) {
for (auto arg : fty.args) {
if (!arg->byref && !isPOD(arg->type))
indirectByvalRewrite.applyTo(*arg);
}
}
workaroundIssue1356(fty.args);
// Clang does not pass empty structs, while it seems that GCC does,
// at least on Linux x86. We don't know whether the C compiler will
// be Clang or GCC, so just assume Clang on OS X and G++ on Linux.
if (externD || !isOSX)
return;
size_t i = 0;
while (i < fty.args.size()) {
Type *type = fty.args[i]->type->toBasetype();
if (type->ty == Tstruct) {
// Do not pass empty structs at all for C++ ABI compatibility.
// Tests with clang reveal that more complex "empty" types, for
// example a struct containing an empty struct, are not
// optimized in the same way.
auto sd = static_cast<TypeStruct *>(type)->sym;
if (sd->fields.empty()) {
fty.args.erase(fty.args.begin() + i);
continue;
}
}
++i;
}
}
