[PATCH v2] typeof: Remove type qualifiers for atomic types

[PATCH v2] typeof: Remove type qualifiers for atomic types

[Sebastian Huber]

GCC provides its own version of stdatomic.h since GCC 4.9.  Here we
have:

  #define atomic_load_explicit(PTR, MO)                    \
    __extension__                                \
    ({                                    \
      __auto_type __atomic_load_ptr = (PTR);                \
      __typeof__ (*__atomic_load_ptr) __atomic_load_tmp;            \
      __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (MO));    \
      __atomic_load_tmp;                            \
    })

According to

http://en.cppreference.com/w/c/atomic/atomic_load

(or in the standard "7.17.7.2 The atomic_load generic functions") we
have

C atomic_load_explicit( volatile A* obj, memory_order order );

This test case

  #include <stdatomic.h>

  int ld(volatile atomic_int *i)
  {
    return atomic_load_explicit(i, memory_order_relaxed);
  }

yields on ARM

arm-rtems4.11-gcc -march=armv7-a -O2 test.c -S && cat test.s
        .arch armv7-a
        .fpu softvfp
        .eabi_attribute 20, 1
        .eabi_attribute 21, 1
        .eabi_attribute 23, 3
        .eabi_attribute 24, 1
        .eabi_attribute 25, 1
        .eabi_attribute 26, 1
        .eabi_attribute 30, 2
        .eabi_attribute 34, 1
        .eabi_attribute 18, 4
        .file   "test.c"
        .text
        .align  2
        .global ld
        .type   ld, %function
ld:
        @ args = 0, pretend = 0, frame = 8
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        ldr     r3, [r0]
        sub     sp, sp, #8
        str     r3, [sp, #4]
        ldr     r0, [sp, #4]
        add     sp, sp, #8
        @ sp needed
        bx      lr
        .size   ld, .-ld
        .ident  "GCC: (GNU) 4.9.1 20140515 (prerelease)

To solve this performance issue discard all qualifiers in __typeof__ and
__auto_type for atomic types.

With this patch we have

rm-rtems4.11-gcc -march=armv7-a -O2 test.c -S && cat test.s
        .arch armv7-a
        .fpu softvfp
        .eabi_attribute 20, 1
        .eabi_attribute 21, 1
        .eabi_attribute 23, 3
        .eabi_attribute 24, 1
        .eabi_attribute 25, 1
        .eabi_attribute 26, 1
        .eabi_attribute 30, 2
        .eabi_attribute 34, 1
        .eabi_attribute 18, 4
        .file   "test.c"
        .text
        .align  2
        .global ld
        .type   ld, %function
ld:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        ldr     r0, [r0]
        bx      lr
        .size   ld, .-ld
        .ident  "GCC: (GNU) 4.9.1 20140625 (prerelease)

gcc/c/ChangeLog
2014-06-26  Sebastian Huber  <sebastian.huber@embedded-brains.de>

	* c-parser.c (c_parser_declaration_or_fndef): Discard all type
	qualifiers in __auto_type for atomic types.
	(c_parser_typeof_specifier): Discard all type qualifiers in
	__typeof__ for atomic types.

gcc/testsuite/ChangeLog
2014-06-26  Sebastian Huber  <sebastian.huber@embedded-brains.de>

	* gcc.dg/typeof-2.c: New testcase.
---
 gcc/c/c-parser.c                |   21 ++++++---------------
 gcc/testsuite/gcc.dg/typeof-2.c |   28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 15 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/typeof-2.c

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 99ff546..037da03 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -1707,14 +1707,10 @@ c_parser_declaration_or_fndef (c_parser *parser, bool fndef_ok,
 			      " initializer");
 		  init = convert_lvalue_to_rvalue (init_loc, init, true, true);
 		  tree init_type = TREE_TYPE (init.value);
-		  /* As with typeof, remove _Atomic and const
-		     qualifiers from atomic types.  */
+		  /* As with typeof, remove all qualifiers from atomic types.  */
 		  if (init_type != error_mark_node && TYPE_ATOMIC (init_type))
 		    init_type
-		      = c_build_qualified_type (init_type,
-						(TYPE_QUALS (init_type)
-						 & ~(TYPE_QUAL_ATOMIC
-						     | TYPE_QUAL_CONST)));
+		      = c_build_qualified_type (init_type, TYPE_UNQUALIFIED);
 		  bool vm_type = variably_modified_type_p (init_type,
 							   NULL_TREE);
 		  if (vm_type)
@@ -3011,16 +3007,11 @@ c_parser_typeof_specifier (c_parser *parser)
       if (was_vm)
 	ret.expr = c_fully_fold (expr.value, false, &ret.expr_const_operands);
       pop_maybe_used (was_vm);
-      /* For use in macros such as those in <stdatomic.h>, remove
-	 _Atomic and const qualifiers from atomic types.  (Possibly
-	 all qualifiers should be removed; const can be an issue for
-	 more macros using typeof than just the <stdatomic.h>
-	 ones.)  */
+      /* For use in macros such as those in <stdatomic.h>, remove all
+	 qualifiers from atomic types.  (const can be an issue for more macros
+	 using typeof than just the <stdatomic.h> ones.)  */
       if (ret.spec != error_mark_node && TYPE_ATOMIC (ret.spec))
-	ret.spec = c_build_qualified_type (ret.spec,
-					   (TYPE_QUALS (ret.spec)
-					    & ~(TYPE_QUAL_ATOMIC
-						| TYPE_QUAL_CONST)));
+	ret.spec = c_build_qualified_type (ret.spec, TYPE_UNQUALIFIED);
     }
   c_parser_skip_until_found (parser, CPP_CLOSE_PAREN, "expected %<)%>");
   return ret;
diff --git a/gcc/testsuite/gcc.dg/typeof-2.c b/gcc/testsuite/gcc.dg/typeof-2.c
new file mode 100644
index 0000000..e916900
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/typeof-2.c
@@ -0,0 +1,28 @@
+/* Test qualifier discard of typeof for atomic types. */
+/* { dg-do compile } */
+/* { dg-options "-std=c11" } */
+
+extern int i;
+
+extern int * p;
+
+extern int _Atomic const ci;
+extern __typeof (ci) i;
+
+extern int _Atomic volatile vi;
+extern __typeof (vi) i;
+
+extern int * _Atomic restrict ri;
+extern __typeof (ri) p;
+
+void f(void)
+{
+  __auto_type aci = ci;
+  int *paci = &aci;
+
+  __auto_type avi = vi;
+  int *pavi = &avi;
+
+  __auto_type ari = ri;
+  int **pari = &ari;
+}
-- 
1.7.7

Re: [PATCH v2] typeof: Remove type qualifiers for atomic types

[Joseph S. Myers]

On Thu, 26 Jun 2014, Sebastian Huber wrote:

> gcc/c/ChangeLog
> 2014-06-26  Sebastian Huber  <sebastian.huber@embedded-brains.de>
> 
> 	* c-parser.c (c_parser_declaration_or_fndef): Discard all type
> 	qualifiers in __auto_type for atomic types.
> 	(c_parser_typeof_specifier): Discard all type qualifiers in
> 	__typeof__ for atomic types.
> 
> gcc/testsuite/ChangeLog
> 2014-06-26  Sebastian Huber  <sebastian.huber@embedded-brains.de>
> 
> 	* gcc.dg/typeof-2.c: New testcase.

OK.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH v2] typeof: Remove type qualifiers for atomic types

[Sebastian Huber]

On 2014-06-26 17:51, Joseph S. Myers wrote:
> On Thu, 26 Jun 2014, Sebastian Huber wrote:
>
>> >gcc/c/ChangeLog
>> >2014-06-26  Sebastian Huber<sebastian.huber@embedded-brains.de>
>> >
>> >	* c-parser.c (c_parser_declaration_or_fndef): Discard all type
>> >	qualifiers in __auto_type for atomic types.
>> >	(c_parser_typeof_specifier): Discard all type qualifiers in
>> >	__typeof__ for atomic types.
>> >
>> >gcc/testsuite/ChangeLog
>> >2014-06-26  Sebastian Huber<sebastian.huber@embedded-brains.de>
>> >
>> >	* gcc.dg/typeof-2.c: New testcase.
> OK.

Thanks for your patience.  It would be nice if this can be applied to GCC 4.9 
as well.

Can someone please commit this for me, since I don't have write access.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

Re: [PATCH v2] typeof: Remove type qualifiers for atomic types

[Marek Polacek]

On Fri, Jun 27, 2014 at 08:36:38AM +0200, Sebastian Huber wrote:
> Thanks for your patience.  It would be nice if this can be applied to GCC
> 4.9 as well.
> 
> Can someone please commit this for me, since I don't have write access.

I will commit it for you.

	Marek

Re: [PATCH v2] typeof: Remove type qualifiers for atomic types

[Marek Polacek]

On Fri, Jun 27, 2014 at 08:49:24AM +0200, Marek Polacek wrote:
> On Fri, Jun 27, 2014 at 08:36:38AM +0200, Sebastian Huber wrote:
> > Thanks for your patience.  It would be nice if this can be applied to GCC
> > 4.9 as well.
> > 
> > Can someone please commit this for me, since I don't have write access.
> 
> I will commit it for you.

Now applied to 4.9 as well.

	Marek

Re: [PATCH v2] typeof: Remove type qualifiers for atomic types

[Sebastian Huber]

On 2014-06-30 15:03, Marek Polacek wrote:
> On Fri, Jun 27, 2014 at 08:49:24AM +0200, Marek Polacek wrote:
>> On Fri, Jun 27, 2014 at 08:36:38AM +0200, Sebastian Huber wrote:
>>> Thanks for your patience.  It would be nice if this can be applied to GCC
>>> 4.9 as well.
>>>
>>> Can someone please commit this for me, since I don't have write access.
>>
>> I will commit it for you.
>
> Now applied to 4.9 as well.
>
> 	Marek
>

Should this __typeof and __auto_type behaviour for atomic types show up in the 
documentation?

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.