On 5/16/22 10:56, Richard Sandiford wrote:
> Martin Liška <mli...@suse.cz> writes:
>> It's the warning I see every time I build GCC:
>>
>> In file included from /home/marxin/Programming/gcc/gcc/coretypes.h:478,
>> from /home/marxin/Programming/gcc/gcc/expmed.cc:26:
>> In function ‘poly_uint16 mode_to_bytes(machine_mode)’,
>> inlined from ‘typename if_nonpoly<typename T::measurement_type>::type
>> GET_MODE_SIZE(const T&) [with T = scalar_int_mode]’ at
>> /home/marxin/Programming/gcc/gcc/machmode.h:647:24,
>> inlined from ‘rtx_def* emit_store_flag_1(rtx, rtx_code, rtx, rtx,
>> machine_mode, int, int, machine_mode)’ at
>> /home/marxin/Programming/gcc/gcc/expmed.cc:5728:56:
>> /home/marxin/Programming/gcc/gcc/machmode.h:550:49: warning: ‘*(unsigned
>> int*)((char*)&int_mode + offsetof(scalar_int_mode,
>> scalar_int_mode::m_mode))’ may be used uninitialized [-Wmaybe-uninitialized]
>> 550 | ? mode_size_inline (mode) : mode_size[mode]);
>> | ^~~~
>> /home/marxin/Programming/gcc/gcc/expmed.cc: In function ‘rtx_def*
>> emit_store_flag_1(rtx, rtx_code, rtx, rtx, machine_mode, int, int,
>> machine_mode)’:
>> /home/marxin/Programming/gcc/gcc/expmed.cc:5657:19: note: ‘*(unsigned
>> int*)((char*)&int_mode + offsetof(scalar_int_mode,
>> scalar_int_mode::m_mode))’ was declared here
>> 5657 | scalar_int_mode int_mode;
>> | ^~~~~~~~
>>
>> Can we please mitigate it?
>>
>> gcc/ChangeLog:
>>
>> * expmed.cc (emit_store_flag_1): Mitigate -Wmaybe-uninitialized
>> warning.
>
> Not a strong objection, but TBH I'd rather we didn't work around false
> positives like this.
Sure, but as you know, -Wmaybe-uninitialized has pretty high rate
of false positivity :/
Martin
>
> Richard
>
>> ---
>> gcc/expmed.cc | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/gcc/expmed.cc b/gcc/expmed.cc
>> index 41738c1efe9..f23d63471ea 100644
>> --- a/gcc/expmed.cc
>> +++ b/gcc/expmed.cc
>> @@ -5654,7 +5654,7 @@ emit_store_flag_1 (rtx target, enum rtx_code code, rtx
>> op0, rtx op1,
>>
>> /* If we are comparing a double-word integer with zero or -1, we can
>> convert the comparison into one involving a single word. */
>> - scalar_int_mode int_mode;
>> + scalar_int_mode int_mode = {};
>> if (is_int_mode (mode, &int_mode)
>> && GET_MODE_BITSIZE (int_mode) == BITS_PER_WORD * 2
>> && (!MEM_P (op0) || ! MEM_VOLATILE_P (op0)))
