[PATCH] Mark asm goto with outputs as volatile

[PATCH] Mark asm goto with outputs as volatile

[Andrew Pinski]

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.

	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

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

[Richard Biener]

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.

>         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
>

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

[Andrew Pinski]

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
> >

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

[Jeff Law]

On 6/27/23 11:23, Andrew Pinski via Gcc-patches wrote:
> 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.
The test should be conditional on target lra since we don't support asm 
goto on the reload targets.

It looks like gcc.dg/pr108095.c needs similar adjustment.  Consider a 
patch to make those adjustments pre-approved.

jeff

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

[Andreas Schwab]

On Jun 26 2023, Andrew Pinski via Gcc-patches wrote:

> 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.  */
               are

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."