Re: [PATCH] c, c++: Allow ignoring -Winit-self through pragmas [PR105593]

[Marek Polacek <polacek@redhat.com>]

On Thu, Jan 12, 2023 at 09:49:56PM -0500, Jason Merrill wrote:
> On 1/12/23 19:32, Jakub Jelinek wrote:
> > Hi!
> > 
> > As mentioned in the PR, various x86 intrinsics need to return
> > an uninitialized vector.  Currently they use self initialization
> > to avoid -Wuninitialized warnings, which works fine in C, but
> > doesn't work in C++ where -Winit-self is enabled in -Wall.
> > We don't have an attribute to mark a variable as knowingly
> > uninitialized (the uninitialized attribute exists but means
> > something else, only in the -ftrivial-auto-var-init context),
> > and trying to suppress either -Wuninitialized or -Winit-self
> > inside of the _mm_undefined_ps etc. intrinsic definitions
> > doesn't work, one needs to currently disable through pragmas
> > -Wuninitialized warning at the point where _mm_undefined_ps etc.
> > result is actually used, but that goes against the intent of
> > those intrinsics.
> > 
> > The -Winit-self warning option actually doesn't do any warning,
> > all we do is record a suppression for -Winit-self if !warn_init_self
> > on the decl definition and later look that up in uninit pass.
> > 
> > The following patch changes those !warn_init_self tests which
> > are true only based on the command line option setting, not based
> > on GCC diagnostic pragma overrides to
> > !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self)
> > such that it takes them into account.
> > 
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> OK on Monday if the C maintainers don't comment.

The C changes LGTM, thanks.
 
> > Will post incremental patch for the intrinsic headers.
> > 
> > 2023-01-13  Jakub Jelinek  <jakub@redhat.com>
> > 
> > 	PR c++/105593
> > gcc/c/
> > 	* c-parser.cc (c_parser_initializer): Check warning_enabled_at
> > 	at the DECL_SOURCE_LOCATION (decl) for OPT_Winit_self instead
> > 	of warn_init_self.
> > gcc/cp/
> > 	* decl.cc (cp_finish_decl): Check warning_enabled_at
> > 	at the DECL_SOURCE_LOCATION (decl) for OPT_Winit_self instead
> > 	of warn_init_self.
> > gcc/testsuite/
> > 	* c-c++-common/Winit-self3.c: New test.
> > 	* c-c++-common/Winit-self4.c: New test.
> > 	* c-c++-common/Winit-self5.c: New test.
> > 
> > --- gcc/c/c-parser.cc.jj	2023-01-11 22:18:25.560492345 +0100
> > +++ gcc/c/c-parser.cc	2023-01-12 15:30:10.460233783 +0100
> > @@ -5701,7 +5701,7 @@ c_parser_initializer (c_parser *parser,
> >   	  && !DECL_EXTERNAL (decl)
> >   	  && !TREE_STATIC (decl)
> >   	  && ret.value == decl
> > -	  && !warn_init_self)
> > +	  && !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self))
> >   	suppress_warning (decl, OPT_Winit_self);
> >         if (TREE_CODE (ret.value) != STRING_CST
> >   	  && (TREE_CODE (ret.value) != COMPOUND_LITERAL_EXPR
> > --- gcc/cp/decl.cc.jj	2023-01-04 18:42:24.597997547 +0100
> > +++ gcc/cp/decl.cc	2023-01-12 15:26:01.257817526 +0100
> > @@ -8407,7 +8407,7 @@ cp_finish_decl (tree decl, tree init, bo
> >         if (!DECL_EXTERNAL (decl)
> >   	  && !TREE_STATIC (decl)
> >   	  && decl == tree_strip_any_location_wrapper (init)
> > -	  && !warn_init_self)
> > +	  && !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self))
> >   	suppress_warning (decl, OPT_Winit_self);
> >       }
> > --- gcc/testsuite/c-c++-common/Winit-self3.c.jj	2023-01-12 15:49:56.759172518 +0100
> > +++ gcc/testsuite/c-c++-common/Winit-self3.c	2023-01-12 15:50:51.512384963 +0100
> > @@ -0,0 +1,36 @@
> > +/* PR c++/105593 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-W -Wall" } */
> > +
> > +void bar (int);
> > +
> > +static inline int
> > +baz (void)
> > +{
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Winit-self"
> > +  int u = u;		/* { dg-bogus "'u' is used uninitialized" } */
> > +#pragma GCC diagnostic pop
> > +  return u;
> > +}
> > +
> > +void
> > +foo (void)
> > +{
> > +  int u = baz ();
> > +  bar (u);
> > +}
> > +
> > +static inline int
> > +qux (void)
> > +{
> > +  int u = u;		/* { dg-warning "'u' is used uninitialized" "" { target c++ } } */
> > +  return u;		/* { dg-message "'u' was declared here" "" { target c++ } .-1 } */
> > +}
> > +
> > +void
> > +corge (void)
> > +{
> > +  int u = qux ();
> > +  bar (u);
> > +}
> > --- gcc/testsuite/c-c++-common/Winit-self4.c.jj	2023-01-12 15:50:15.233906776 +0100
> > +++ gcc/testsuite/c-c++-common/Winit-self4.c	2023-01-12 15:50:42.445515372 +0100
> > @@ -0,0 +1,36 @@
> > +/* PR c++/105593 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-W -Wall -Winit-self" } */
> > +
> > +void bar (int);
> > +
> > +static inline int
> > +baz (void)
> > +{
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Winit-self"
> > +  int u = u;		/* { dg-bogus "'u' is used uninitialized" } */
> > +#pragma GCC diagnostic pop
> > +  return u;
> > +}
> > +
> > +void
> > +foo (void)
> > +{
> > +  int u = baz ();
> > +  bar (u);
> > +}
> > +
> > +static inline int
> > +qux (void)
> > +{
> > +  int u = u;		/* { dg-warning "'u' is used uninitialized" } */
> > +  return u;		/* { dg-message "'u' was declared here" "" { target *-*-* } .-1 } */
> > +}
> > +
> > +void
> > +corge (void)
> > +{
> > +  int u = qux ();
> > +  bar (u);
> > +}
> > --- gcc/testsuite/c-c++-common/Winit-self5.c.jj	2023-01-12 15:51:01.045247847 +0100
> > +++ gcc/testsuite/c-c++-common/Winit-self5.c	2023-01-12 15:51:12.929076923 +0100
> > @@ -0,0 +1,36 @@
> > +/* PR c++/105593 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-W -Wall -Wno-init-self" } */
> > +
> > +void bar (int);
> > +
> > +static inline int
> > +baz (void)
> > +{
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Winit-self"
> > +  int u = u;		/* { dg-bogus "'u' is used uninitialized" } */
> > +#pragma GCC diagnostic pop
> > +  return u;
> > +}
> > +
> > +void
> > +foo (void)
> > +{
> > +  int u = baz ();
> > +  bar (u);
> > +}
> > +
> > +static inline int
> > +qux (void)
> > +{
> > +  int u = u;		/* { dg-bogus "'u' is used uninitialized" } */
> > +  return u;
> > +}
> > +
> > +void
> > +corge (void)
> > +{
> > +  int u = qux ();
> > +  bar (u);
> > +}
> > 
> > 	Jakub
> > 
> 

Marek