c++, v2: Don't defer local statics initialized with constant expressions [PR108702]
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On Thu, Mar 02, 2023 at 11:48:04AM -0500, Jason Merrill wrote:
> > The stmtexpr19.C testcase used to be rejected as it has a static
> > variable in statement expression in constexpr context, but as that
> > static variable is initialized by constant expression, when P2647R1
> > was implemented we agreed to make it valid.
> >
> > Now, as reported, the testcase compiles fine, but doesn't actually link
> > because the static variable isn't defined anywhere, and with -flto ICEs
> > because of this problem. This is because we never
> > varpool_node::finalize_decl those vars, the constant expression in which
> > the DECL_EXPR is present for the static VAR_DECL is folded (constant
> > evaluated) into just the address of the VAR_DECL.
>
> Would it make sense to define it when we see the DECL_EXPR in constant
> evaluation?
So like this?
Passes GXX_TESTSUITE_STDS=98,11,14,17,20,2b make check-g++ so far.
2023-03-03 Jakub Jelinek <jakub@redhat.com>
PR c++/108702
* constexpr.cc: Include toplev.h.
(cxx_eval_constant_expression) <case DECL_EXPR>: When seeing a local
static initialized by constant expression outside of a constexpr
function which has been deferred by make_rtl_for_nonlocal_decl,
call rest_of_decl_compilation on it.
* g++.dg/ext/stmtexpr19.C: Use dg-do link rather than dg-do compile.
Jakub
Comments
On 3/3/23 10:18, Jakub Jelinek wrote:
> On Thu, Mar 02, 2023 at 11:48:04AM -0500, Jason Merrill wrote:
>>> The stmtexpr19.C testcase used to be rejected as it has a static
>>> variable in statement expression in constexpr context, but as that
>>> static variable is initialized by constant expression, when P2647R1
>>> was implemented we agreed to make it valid.
>>>
>>> Now, as reported, the testcase compiles fine, but doesn't actually link
>>> because the static variable isn't defined anywhere, and with -flto ICEs
>>> because of this problem. This is because we never
>>> varpool_node::finalize_decl those vars, the constant expression in which
>>> the DECL_EXPR is present for the static VAR_DECL is folded (constant
>>> evaluated) into just the address of the VAR_DECL.
>>
>> Would it make sense to define it when we see the DECL_EXPR in constant
>> evaluation?
>
> So like this?
OK, thanks.
> Passes GXX_TESTSUITE_STDS=98,11,14,17,20,2b make check-g++ so far.
>
> 2023-03-03 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/108702
> * constexpr.cc: Include toplev.h.
> (cxx_eval_constant_expression) <case DECL_EXPR>: When seeing a local
> static initialized by constant expression outside of a constexpr
> function which has been deferred by make_rtl_for_nonlocal_decl,
> call rest_of_decl_compilation on it.
>
> * g++.dg/ext/stmtexpr19.C: Use dg-do link rather than dg-do compile.
>
> --- gcc/cp/constexpr.cc.jj 2023-03-03 00:34:44.113679918 +0100
> +++ gcc/cp/constexpr.cc 2023-03-03 13:26:57.602871900 +0100
> @@ -40,6 +40,7 @@ along with GCC; see the file COPYING3.
> #include "attribs.h"
> #include "fold-const.h"
> #include "intl.h"
> +#include "toplev.h"
>
> static bool verify_constant (tree, bool, bool *, bool *);
> #define VERIFY_CONSTANT(X) \
> @@ -7127,6 +7128,24 @@ cxx_eval_constant_expression (const cons
> break;
> }
>
> + /* make_rtl_for_nonlocal_decl could have deferred emission of
> + a local static var, but if it appears in a statement expression
> + which is constant expression evaluated to e.g. just the address
> + of the variable, its DECL_EXPR will never be seen during
> + gimple lowering's record_vars_into as the statement expression
> + will not be in the IL at all. */
> + if (VAR_P (r)
> + && TREE_STATIC (r)
> + && !DECL_REALLY_EXTERN (r)
> + && DECL_FUNCTION_SCOPE_P (r)
> + && !var_in_maybe_constexpr_fn (r)
> + && decl_constant_var_p (r))
> + {
> + varpool_node *node = varpool_node::get (r);
> + if (node == NULL || !node->definition)
> + rest_of_decl_compilation (r, 0, at_eof);
> + }
> +
> if (AGGREGATE_TYPE_P (TREE_TYPE (r))
> || VECTOR_TYPE_P (TREE_TYPE (r)))
> {
> --- gcc/testsuite/g++.dg/ext/stmtexpr19.C.jj 2023-02-09 15:52:29.623359240 +0100
> +++ gcc/testsuite/g++.dg/ext/stmtexpr19.C 2023-03-03 12:24:20.217186735 +0100
> @@ -1,6 +1,6 @@
> // PR c++/81073
> // { dg-options "" }
> -// { dg-do compile { target c++11 } }
> +// { dg-do link { target c++11 } }
>
> struct test { const int *addr; };
>
>
>
> Jakub
>
@@ -40,6 +40,7 @@ along with GCC; see the file COPYING3.
#include "attribs.h"
#include "fold-const.h"
#include "intl.h"
+#include "toplev.h"
static bool verify_constant (tree, bool, bool *, bool *);
#define VERIFY_CONSTANT(X) \
@@ -7127,6 +7128,24 @@ cxx_eval_constant_expression (const cons
break;
}
+ /* make_rtl_for_nonlocal_decl could have deferred emission of
+ a local static var, but if it appears in a statement expression
+ which is constant expression evaluated to e.g. just the address
+ of the variable, its DECL_EXPR will never be seen during
+ gimple lowering's record_vars_into as the statement expression
+ will not be in the IL at all. */
+ if (VAR_P (r)
+ && TREE_STATIC (r)
+ && !DECL_REALLY_EXTERN (r)
+ && DECL_FUNCTION_SCOPE_P (r)
+ && !var_in_maybe_constexpr_fn (r)
+ && decl_constant_var_p (r))
+ {
+ varpool_node *node = varpool_node::get (r);
+ if (node == NULL || !node->definition)
+ rest_of_decl_compilation (r, 0, at_eof);
+ }
+
if (AGGREGATE_TYPE_P (TREE_TYPE (r))
|| VECTOR_TYPE_P (TREE_TYPE (r)))
{
@@ -1,6 +1,6 @@
// PR c++/81073
// { dg-options "" }
-// { dg-do compile { target c++11 } }
+// { dg-do link { target c++11 } }
struct test { const int *addr; };