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Improve handling of ignored function call return values #16046

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Merged
merged 2 commits into from
Jul 29, 2014
Merged

Improve handling of ignored function call return values #16046

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39135ec
Omit unnecessary stack slots for ignored return values
dotdash Jul 28, 2014
a1c95ec
Emit lifetime end markers for allocas for ignored return values
dotdash Jul 28, 2014
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21 changes: 12 additions & 9 deletions src/librustc/middle/trans/callee.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -775,6 +775,8 @@ pub fn trans_call_inner<'a>(
// We trans them in place in `trans_intrinsic_call`
assert!(abi != synabi::RustIntrinsic);

let is_rust_fn = abi == synabi::Rust || abi == synabi::RustCall;

// Generate a location to store the result. If the user does
// not care about the result, just make a stack slot.
let opt_llretslot = match dest {
Expand All @@ -783,14 +785,17 @@ pub fn trans_call_inner<'a>(
None
}
Some(expr::SaveIn(dst)) => Some(dst),
Some(expr::Ignore) => {
Some(expr::Ignore) if !is_rust_fn ||
type_of::return_uses_outptr(ccx, ret_ty) ||
ty::type_needs_drop(bcx.tcx(), ret_ty) => {
if !type_is_zero_size(ccx, ret_ty) {
Some(alloc_ty(bcx, ret_ty, "__llret"))
} else {
let llty = type_of::type_of(ccx, ret_ty);
Some(C_undef(llty.ptr_to()))
}
}
Some(expr::Ignore) => None
};

let mut llresult = unsafe {
Expand All @@ -803,7 +808,7 @@ pub fn trans_call_inner<'a>(
// and done, either the return value of the function will have been
// written in opt_llretslot (if it is Some) or `llresult` will be
// set appropriately (otherwise).
if abi == synabi::Rust || abi == synabi::RustCall {
if is_rust_fn {
let mut llargs = Vec::new();

// Push the out-pointer if we use an out-pointer for this
Expand Down Expand Up @@ -878,15 +883,13 @@ pub fn trans_call_inner<'a>(

// If the caller doesn't care about the result of this fn call,
// drop the temporary slot we made.
match dest {
None => {
assert!(!type_of::return_uses_outptr(bcx.ccx(), ret_ty));
}
Some(expr::Ignore) => {
match (dest, opt_llretslot) {
(Some(expr::Ignore), Some(llretslot)) => {
// drop the value if it is not being saved.
bcx = glue::drop_ty(bcx, opt_llretslot.unwrap(), ret_ty);
bcx = glue::drop_ty(bcx, llretslot, ret_ty);
call_lifetime_end(bcx, llretslot);
}
Some(expr::SaveIn(_)) => { }
_ => {}
}

if ty::type_is_bot(ret_ty) {
Expand Down