Re: [PATCH] Mark asm goto with outputs as volatile

[Andrew Pinski <pinskia@gmail.com>]

On Tue, Jun 27, 2023 at 12:14 AM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Tue, Jun 27, 2023 at 5:26 AM Andrew Pinski via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > The manual references asm goto as being implicitly volatile already
> > and that was done when asm goto could not have outputs. When outputs
> > were added to `asm goto`, only asm goto without outputs were still being
> > marked as volatile. Now some parts of GCC decide, removing the `asm goto`
> > is ok if the output is not used, though not updating the CFG (this happens
> > on both the RTL level and the gimple level). Since the biggest user of `asm goto`
> > is the Linux kernel and they expect them to be volatile (they use them to
> > copy to/from userspace), we should just mark the inline-asm as volatile.
> >
> > OK? Bootstrapped and tested on x86_64-linux-gnu.
>
> OK.

Committed to GCC 12 and GCC 13 branches also.

Thanks,
Andrew

>
> >         PR middle-end/110420
> >         PR middle-end/103979
> >         PR middle-end/98619
> >
> > gcc/ChangeLog:
> >
> >         * gimplify.cc (gimplify_asm_expr): Mark asm with labels as volatile.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.c-torture/compile/asmgoto-6.c: New test.
> > ---
> >  gcc/gimplify.cc                               |  7 ++++-
> >  .../gcc.c-torture/compile/asmgoto-6.c         | 26 +++++++++++++++++++
> >  2 files changed, 32 insertions(+), 1 deletion(-)
> >  create mode 100644 gcc/testsuite/gcc.c-torture/compile/asmgoto-6.c
> >
> > diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
> > index 0e24b915b8f..dc6a00e8bd9 100644
> > --- a/gcc/gimplify.cc
> > +++ b/gcc/gimplify.cc
> > @@ -6935,7 +6935,12 @@ gimplify_asm_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
> >        stmt = gimple_build_asm_vec (TREE_STRING_POINTER (ASM_STRING (expr)),
> >                                    inputs, outputs, clobbers, labels);
> >
> > -      gimple_asm_set_volatile (stmt, ASM_VOLATILE_P (expr) || noutputs == 0);
> > +      /* asm is volatile if it was marked by the user as volatile or
> > +        there is no outputs or this is an asm goto.  */
> > +      gimple_asm_set_volatile (stmt,
> > +                              ASM_VOLATILE_P (expr)
> > +                              || noutputs == 0
> > +                              || labels);
> >        gimple_asm_set_input (stmt, ASM_INPUT_P (expr));
> >        gimple_asm_set_inline (stmt, ASM_INLINE_P (expr));
> >
> > diff --git a/gcc/testsuite/gcc.c-torture/compile/asmgoto-6.c b/gcc/testsuite/gcc.c-torture/compile/asmgoto-6.c
> > new file mode 100644
> > index 00000000000..0652bd4e4e1
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.c-torture/compile/asmgoto-6.c
> > @@ -0,0 +1,26 @@
> > +
> > +/* { dg-do compile } */
> > +/* PR middle-end/110420 */
> > +/* PR middle-end/103979 */
> > +/* PR middle-end/98619 */
> > +/* Test that the middle-end does not remove the asm goto
> > +   with an output. */
> > +
> > +static int t;
> > +void g(void);
> > +
> > +void f(void)
> > +{
> > +  int  __gu_val;
> > +  asm goto("#my asm "
> > +     : "=&r"(__gu_val)
> > +     :
> > +     :
> > +     : Efault);
> > +  t = __gu_val;
> > +  g();
> > +Efault:
> > +}
> > +
> > +/* Make sure "my asm " is still in the assembly. */
> > +/* { dg-final { scan-assembler "my asm " } } */
> > --
> > 2.31.1
> >