Re: [PATCH] Basic asm blocks should always be volatile

[Andrew Pinski <pinskia@gmail.com>]

On Tue, Jun 27, 2023 at 9:15 AM Julian Waters <tanksherman27@gmail.com> wrote:
>
> Hi Andrew,
>
> That can't be right, on my system a test of asm vs asm volatile with -O3 and -flto=auto yields very different results, with only the latter being correct. The patch fixed it and caused gcc to emit correct assembly

Can you provide a few testcases? Because the gimplifier should always happen.

Thanks,
Andrew Pinski

>
> best regards,
> Julian
>
> On Wed, Jun 28, 2023 at 12:08 AM Andrew Pinski <pinskia@gmail.com> wrote:
>>
>> On Tue, Jun 27, 2023 at 9:03 AM Julian Waters via Gcc <gcc@gcc.gnu.org> wrote:
>> >
>> > gcc's documentatation mentions that all basic asm blocks are always volatile,
>> > yet the parser fails to account for this by only ever setting
>> > volatile_p to true
>> > if the volatile qualifier is found. This patch fixes this by adding a
>> > special case check for extended_p before finish_asm_statement is called
>>
>> The patch which are you doing will not change the behavior of GCC as
>> GCC already treats them as volatile later on.
>> non-extended inline-asm has no outputs so the following code in the
>> gimplifier will kick in and turn the gimple statement into volatile:
>>       gimple_asm_set_volatile (stmt, ASM_VOLATILE_P (expr) || noutputs == 0);
>>
>> (note I am about to push a patch which changes the condition slightly
>> to have `asm goto` as volatile).
>>
>> Thanks,
>> Andrew
>>
>> >
>> > From 3094be39e3e65a6a638f05fafd858b89fefde6b5 Mon Sep 17 00:00:00 2001
>> > From: TheShermanTanker <tanksherman27@gmail.com>
>> > Date: Tue, 27 Jun 2023 23:56:38 +0800
>> > Subject: [PATCH] asm not using extended syntax should always be volatile
>> >
>> > ---
>> >  gcc/cp/parser.cc | 3 +++
>> >  1 file changed, 3 insertions(+)
>> >
>> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
>> > index a6341b9..ef3d06a 100644
>> > --- a/gcc/cp/parser.cc
>> > +++ b/gcc/cp/parser.cc
>> > @@ -22355,6 +22355,9 @@ cp_parser_asm_definition (cp_parser* parser)
>> >        /* Create the ASM_EXPR.  */
>> >        if (parser->in_function_body)
>> >   {
>> > +          if (!extended_p) {
>> > +            volatile_p = true;
>> > +          }
>> >     asm_stmt = finish_asm_stmt (asm_loc, volatile_p, string, outputs,
>> >         inputs, clobbers, labels, inline_p);
>> >     /* If the extended syntax was not used, mark the ASM_EXPR.  */
>> > --
>> > 2.35.1.windows.2