[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[davek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

Dave Korn <davek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2010.12.08 14:10:43
                 CC|                            |davek at gcc dot gnu.org
         AssignedTo|unassigned at gcc dot       |davek at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #6 from Dave Korn <davek at gcc dot gnu.org> 2010-12-08 14:10:43 UTC ---
I stumbled into the underlying cause of this bug while working on
dllimport/dllexport attributes.  It turns out that the TARGET_INSERT_ATTRIBUTES
hook is broken in C++, because of a bit of premature optimisation in the
routine gcc/cp/decl2.c#cplus_decl_attributes().  This is a C++-specific wrapper
round the core compiler's gcc/attribs.c#decl_attributes() which takes care of
deferred attribute handling for templates:

/* Like decl_attributes, but handle C++ complexity.  */

void
cplus_decl_attributes (tree *decl, tree attributes, int flags)
{
  if (*decl == NULL_TREE || *decl == void_type_node
      || *decl == error_mark_node
      || attributes == NULL_TREE)
    return;

  if (processing_template_decl)
    {
      if (check_for_bare_parameter_packs (attributes))
    return;

      save_template_attributes (&attributes, decl);
      if (attributes == NULL_TREE)
    return;
    }

  if (TREE_CODE (*decl) == TEMPLATE_DECL)
    decl = &DECL_TEMPLATE_RESULT (*decl);

  decl_attributes (decl, attributes, flags);

  if (TREE_CODE (*decl) == TYPE_DECL)
    SET_IDENTIFIER_TYPE_VALUE (DECL_NAME (*decl), TREE_TYPE (*decl));
}

  The early exits when attributes == NULL_TREE are (I suppose) intended to save
the time taken calling decl_attributes when there aren't any attributes to be
added to the newly-created decl, but it has the side-effect of bypassing the
call that decl_attributes makes to TARGET_INSERT_ATTRIBUTES.  The consequence
is that the default/target/pragma-derived attributes don't get inserted onto
any decls in C++ - except for decls that have some explicit attributes
specified!

  I'm going to be testing this fix as part of a larger patch over the next
couple of days, perhaps others would like to give it a try on their platforms:


Index: gcc/cp/decl2.c
===================================================================
--- gcc/cp/decl2.c    (revision 167484)
+++ gcc/cp/decl2.c    (working copy)
@@ -1269,8 +1269,7 @@ void
 cplus_decl_attributes (tree *decl, tree attributes, int flags)
 {
   if (*decl == NULL_TREE || *decl == void_type_node
-      || *decl == error_mark_node
-      || attributes == NULL_TREE)
+      || *decl == error_mark_node)
     return;

   if (processing_template_decl)
@@ -1279,13 +1278,13 @@ cplus_decl_attributes (tree *decl, tree attributes
     return;

       save_template_attributes (&attributes, decl);
-      if (attributes == NULL_TREE)
-    return;
     }

   if (TREE_CODE (*decl) == TEMPLATE_DECL)
     decl = &DECL_TEMPLATE_RESULT (*decl);

+  /* Even if ATTRIBUTES is null, we must call this in order to
+     give the TARGET_INSERT_ATTRIBUTES hook a chance to run.  */
   decl_attributes (decl, attributes, flags);

   if (TREE_CODE (*decl) == TYPE_DECL)

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[davek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

--- Comment #7 from Dave Korn <davek at gcc dot gnu.org> 2010-12-08 14:19:40 UTC ---
(In reply to comment #6)
> I stumbled into the underlying cause of this bug 

Should clarify: I'm referring to the broken-ness referred to in comments 1 and
4.  My patch probably won't make any difference to the original testcase,
because it's to do with declarations, not preprocessor macros.

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[davek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

Dave Korn <davek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|davek at gcc dot gnu.org    |unassigned at gcc dot
                   |                            |gnu.org

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[gb.devel at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

Gwenole Beauchesne <gb.devel at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gb.devel at gmail dot com

--- Comment #8 from Gwenole Beauchesne <gb.devel at gmail dot com> ---
Hi, this is a duplicate of PR preprocessor/87299, which is now fixed for GCC
14.

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |87299
   Target Milestone|---                         |14.0
                 CC|                            |lhyatt at gcc dot gnu.org
           See Also|https://gcc.gnu.org/bugzill |
                   |a/show_bug.cgi?id=87299     |


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87299
[Bug 87299] #pragma GCC target behaves differently when using -save-temps

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #9 from Sam James <sjames at gcc dot gnu.org> ---
Fixed for 14. Thanks!

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[justin dot lebar+bug at gmail dot com]

------- Comment #5 from justin dot lebar+bug at gmail dot com  2010-07-26 16:20 -------
FWIW, it seems that MSVC is perfectly happy to compile code with intrinsics
inside a file which doesn't have any special flags.  It would be awesome if
there were some way to do the same with GCC, even if it involves #pragma
hackery.  The current limitation makes using intrinsics pretty painful, as it
requires a separate file for each targeted instruction set.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[hjl dot tools at gmail dot com]

------- Comment #4 from hjl dot tools at gmail dot com  2010-07-12 22:43 -------
I think the whole "pragma GCC target" is incomplete/broken.


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|hjl at gcc dot gnu dot org  |hjl dot tools at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[justin dot lebar+bug at gmail dot com]

------- Comment #3 from justin dot lebar+bug at gmail dot com  2010-07-12 22:22 -------
Also cc'ing H.J. Lu, who wrote sse-23.c


-- 

justin dot lebar+bug at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[justin dot lebar+bug at gmail dot com]

------- Comment #2 from justin dot lebar+bug at gmail dot com  2010-07-12 22:09 -------
cc'ing Harsha Jagasia, who wrote sse-22.c and funcspec-9.

I might be willing to put together a patch for this, but I'm totally unfamiliar
with the codebase, so I'd almost surely need some help.


-- 

justin dot lebar+bug at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harsha dot jagasia at amd
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201

[Bug c++/41201] #pragma GCC target ("sse2") doesn't alter __SSE2__ in C++ (as it does in C)

[siarhei dot siamashka at gmail dot com]

------- Comment #1 from siarhei dot siamashka at gmail dot com  2010-04-27 22:44 -------
"#pragma GCC <target|optimize>" just does not seem to work with C++. Just
stumbled on it trying to narrow down something that looks like wrong-code
generation bug in gcc 4.5.0 when compiling qt4.

Prepending "__attribute__((optimize("-O0")))" to each function still works, so
no real need to go through the trouble of splitting source files into parts to
bisect the issue.


-- 

siarhei dot siamashka at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |siarhei dot siamashka at
                   |                            |gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41201