I like to ping this patch.

Am Freitag, dem 09.08.2024 um 10:20 +0200 schrieb Martin Uecker:
> ok?
> 
> Am Samstag, dem 29.06.2024 um 20:30 +0200 schrieb Martin Uecker:
> > Probably not entirely fool-proof when using statement
> > expressions in initializers, but should be good enough.
> > 
> > 
> > Bootstrapped and regression tested on x86_64.
> > 
> > 
> > 
> >     c: Diagnose declarations that are used only in their own initializer 
> > [PR115027]
> >     
> >     Track the declaration that is currently being initialized and do not
> >     mark it as read when it is used in its own initializer.  This then
> >     allows it to be diagnosed as set-but-unused when it is not used
> >     elsewhere.
> >     
> >             PR c/115027
> >     
> >     gcc/c/
> >             * c-tree.h (in_decl_init): Declare variable.
> >             * c-parser.cc (c_parser_initializer): Record decl being 
> > initialized.
> >             * c-typeck.cc (in_decl_init): Defintie variable.
> >             (mark_exp_read): Ignore decl currently being initialized.
> >     
> >     gcc/testsuite/
> >             * gcc.dg/pr115027.c: New test.
> > 
> > diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
> > index 8c4e697a4e1..46060665115 100644
> > --- a/gcc/c/c-parser.cc
> > +++ b/gcc/c/c-parser.cc
> > @@ -6126,11 +6126,14 @@ c_parser_type_name (c_parser *parser, bool 
> > alignas_ok)
> >  static struct c_expr
> >  c_parser_initializer (c_parser *parser, tree decl)
> >  {
> > +  struct c_expr ret;
> > +  tree save = in_decl_init;
> > +  in_decl_init = decl;
> > +
> >    if (c_parser_next_token_is (parser, CPP_OPEN_BRACE))
> > -    return c_parser_braced_init (parser, NULL_TREE, false, NULL, decl);
> > +    ret = c_parser_braced_init (parser, NULL_TREE, false, NULL, decl);
> >    else
> >      {
> > -      struct c_expr ret;
> >        location_t loc = c_parser_peek_token (parser)->location;
> >        ret = c_parser_expr_no_commas (parser, NULL);
> >        if (decl != error_mark_node && C_DECL_VARIABLE_SIZE (decl))
> > @@ -6154,8 +6157,9 @@ c_parser_initializer (c_parser *parser, tree decl)
> >           || C_DECL_DECLARED_CONSTEXPR (COMPOUND_LITERAL_EXPR_DECL
> >                                         (ret.value))))
> >     ret = convert_lvalue_to_rvalue (loc, ret, true, true, true);
> > -      return ret;
> >      }
> > +    in_decl_init = save;
> > +    return ret;
> >  }
> >  
> >  /* The location of the last comma within the current initializer list,
> > diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> > index 15da875a029..8013963b06d 100644
> > --- a/gcc/c/c-tree.h
> > +++ b/gcc/c/c-tree.h
> > @@ -740,6 +740,8 @@ extern int in_typeof;
> >  extern bool c_in_omp_for;
> >  extern bool c_omp_array_section_p;
> >  
> > +extern tree in_decl_init;
> > +
> >  extern tree c_last_sizeof_arg;
> >  extern location_t c_last_sizeof_loc;
> >  
> > diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
> > index 455dc374b48..34279dc1d1a 100644
> > --- a/gcc/c/c-typeck.cc
> > +++ b/gcc/c/c-typeck.cc
> > @@ -73,6 +73,9 @@ int in_sizeof;
> >  /* The level of nesting inside "typeof".  */
> >  int in_typeof;
> >  
> > +/* When inside an initializer, this is set to the decl being initialized.  
> > */
> > +tree in_decl_init;
> > +
> >  /* True when parsing OpenMP loop expressions.  */
> >  bool c_in_omp_for;
> >  
> > @@ -2047,7 +2050,8 @@ mark_exp_read (tree exp)
> >      {
> >      case VAR_DECL:
> >      case PARM_DECL:
> > -      DECL_READ_P (exp) = 1;
> > +      if (exp != in_decl_init)
> > +   DECL_READ_P (exp) = 1;
> >        break;
> >      case ARRAY_REF:
> >      case COMPONENT_REF:
> > diff --git a/gcc/testsuite/gcc.dg/pr115027.c 
> > b/gcc/testsuite/gcc.dg/pr115027.c
> > new file mode 100644
> > index 00000000000..ac2699f8392
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/pr115027.c
> > @@ -0,0 +1,8 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-Wunused-but-set-variable" } */
> > +
> > +void f(void)
> > +{
> > +   struct foo { void *p; };
> > +   struct foo g = { &g };  /* { dg-warning "set but not used" } */
> > +}
> > 
> 

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