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Avoid unnecessary scratch datums for by-copy function arguments #7237

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Avoid unnecessary scratch datums for by-copy function arguments #7237

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43 changes: 27 additions & 16 deletions src/librustc/middle/trans/callee.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -828,22 +828,33 @@ pub fn trans_arg_expr(bcx: block,
ty::ByCopy => {
debug!("by copy arg with type %s, storing to scratch",
bcx.ty_to_str(arg_datum.ty));
let scratch = scratch_datum(bcx, arg_datum.ty, false);

arg_datum.store_to_datum(bcx,
arg_expr.id,
INIT,
scratch);

// Technically, ownership of val passes to the callee.
// However, we must cleanup should we fail before the
// callee is actually invoked.
scratch.add_clean(bcx);
temp_cleanups.push(scratch.val);

match arg_datum.appropriate_mode() {
ByValue => val = Load(bcx, scratch.val),
ByRef(_) => val = scratch.val,
if ty::type_needs_drop(bcx.tcx(), arg_datum.ty) ||
arg_datum.appropriate_mode().is_by_ref() {
debug!("by copy arg with type %s, storing to scratch",
bcx.ty_to_str(arg_datum.ty));
let scratch = scratch_datum(bcx, arg_datum.ty, false);

arg_datum.store_to_datum(bcx,
arg_expr.id,
INIT,
scratch);

// Technically, ownership of val passes to the callee.
// However, we must cleanup should we fail before the
// callee is actually invoked.
scratch.add_clean(bcx);
temp_cleanups.push(scratch.val);

match scratch.appropriate_mode() {
ByValue => val = Load(bcx, scratch.val),
ByRef(_) => val = scratch.val,
}
} else {
debug!("by copy arg with type %s");
match arg_datum.mode {
ByRef(_) => val = Load(bcx, arg_datum.val),
ByValue => val = arg_datum.val,
}
}
}
}
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