https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99122
--- Comment #34 from Richard Biener <rguenth at gcc dot gnu.org> ---
interestingly I see
a.9_70 = .builtin_alloca_with_align (iftmp.8_1, 8);
(*a.9_70) = inline22.get_zero (); [static-chain: &FRAME.20] [return slot
optimization]
so there's no WITH_SIZE_EXPR, but the return value ends up done by reference:
leaq -80(%rbp), %rdx
movq %rdx, %r10
movq %rax, %rdi
call inline22__get_zero.0
movq %rbx, %rsp
movq -8(%rbp), %rbx
leave
so I wonder if omitting DECL_BY_REFERENCE is simply a bug? I mean the
ABI of the callee must be aware and it seems CALL_EXPR_RETURN_SLOT_OPT
is set by gimplification. IIRC CALL_EXPR_RETURN_SLOT_OPT also only means
we _may_ return by reference not that we must.
/* In a CALL_EXPR, means that it's safe to use the target of the call
expansion as the return slot for a call that returns in memory. */
#define CALL_EXPR_RETURN_SLOT_OPT(NODE) \
(CALL_EXPR_CHECK (NODE)->base.private_flag)
But of course if we do not exercise the return slot opt then there definitely
is a WITH_SIZE_EXPR missing. Unless I'm missing somehting ...
The gimplifier code checks
else if (TREE_CODE (*to_p) != SSA_NAME
&& (!is_gimple_variable (*to_p)
|| needs_to_live_in_memory (*to_p)))
/* Don't use the original target if it's already addressable;
if its address escapes, and the called function uses the
NRV optimization, a conforming program could see *to_p
change before the called function returns; see c++/19317.
When optimizing, the return_slot pass marks more functions
as safe after we have escape info. */
use_target = false;
so I wonder if you can modify the Ada testcase so that
CALL_EXPR_RETURN_SLOT_OPT is not set?
