Re: [PATCH v2] c++: wrong error with static constexpr var in tmpl [PR109876]
On 7/13/23 14:54, Marek Polacek wrote:
On Fri, May 26, 2023 at 09:47:10PM -0400, Jason Merrill wrote:
On 5/26/23 19:18, Marek Polacek wrote:
The is_really_empty_class check is sort of non-obvious but the
comment should explain why I added it.
+ /* When there's nothing to initialize, we'll never mark the
+ VAR_DECL TREE_CONSTANT, therefore it would remain
+ value-dependent and we wouldn't instantiate. */
Sorry it's taken so long to get back to this.
Interesting. Can we change that (i.e. mark it TREE_CONSTANT) rather than
work around it here?
I think we can. Maybe as in the below:
-- >8 --
Since r8-509, we'll no longer create a static temporary var for
the initializer '{ 1, 2 }' for num in the attached test because
the code in finish_compound_literal is now guarded by
'&& fcl_context == fcl_c99' but it's fcl_functional here. This
causes us to reject num as non-constant when evaluating it in
a template.
Jason's idea was to treat num as value-dependent even though it
actually isn't. This patch implements that suggestion.
We weren't marking objects whose type is an empty class type
constant. This patch changes that so that v_d_e_p doesn't need
to check is_really_empty_class.
Co-authored-by: Jason Merrill
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK, thanks.
Incidentally, I prefer to put the "ok?" line above the scissors line
since it isn't intended to be part of the commit message.
PR c++/109876
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Set TREE_CONSTANT when initializing
an object of empty class type.
* pt.cc (value_dependent_expression_p) : Treat a
constexpr-declared non-constant variable as value-dependent.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-template12.C: New test.
* g++.dg/cpp1z/constexpr-template1.C: New test.
* g++.dg/cpp1z/constexpr-template2.C: New test.
---
gcc/cp/decl.cc| 13 +--
gcc/cp/pt.cc | 7
.../g++.dg/cpp0x/constexpr-template12.C | 38 +++
.../g++.dg/cpp1z/constexpr-template1.C| 25
.../g++.dg/cpp1z/constexpr-template2.C| 25
5 files changed, 105 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 60f107d50c4..792ab330dd0 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -8200,7 +8200,6 @@ void
cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
tree asmspec_tree, int flags)
{
- tree type;
vec *cleanups = NULL;
const char *asmspec = NULL;
int was_readonly = 0;
@@ -8220,7 +8219,7 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
/* Parameters are handled by store_parm_decls, not cp_finish_decl. */
gcc_assert (TREE_CODE (decl) != PARM_DECL);
- type = TREE_TYPE (decl);
+ tree type = TREE_TYPE (decl);
if (type == error_mark_node)
return;
@@ -8410,7 +8409,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
if (decl_maybe_constant_var_p (decl)
/* FIXME setting TREE_CONSTANT on refs breaks the back end. */
&& !TYPE_REF_P (type))
- TREE_CONSTANT (decl) = 1;
+ TREE_CONSTANT (decl) = true;
}
/* This is handled mostly by gimplify.cc, but we have to deal with
not warning about int x = x; as it is a GCC extension to turn off
@@ -8421,6 +8420,14 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
&& !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self))
suppress_warning (decl, OPT_Winit_self);
}
+ else if (VAR_P (decl)
+ && COMPLETE_TYPE_P (type)
+ && !TYPE_REF_P (type)
+ && !dependent_type_p (type)
+ && is_really_empty_class (type, /*ignore_vptr*/false))
+/* We have no initializer but there's nothing to initialize anyway.
+ Treat DECL as constant due to c++/109876. */
+TREE_CONSTANT (decl) = true;
if (flag_openmp
&& TREE_CODE (decl) == FUNCTION_DECL
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fa15b75b9c5..255d18b9539 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -27983,6 +27983,13 @@ value_dependent_expression_p (tree expression)
else if (TYPE_REF_P (TREE_TYPE (expression)))
/* FIXME cp_finish_decl doesn't fold reference initializers. */
return true;
+ /* We have a constexpr variable and we're processing a template. When
+there's lifetime extension involved (for which finish_compound_literal
+used to create a temporary), we'll not be able to evaluate the
+variable until instantiating, so
[PATCH v2] c++: wrong error with static constexpr var in tmpl [PR109876]
On Fri, May 26, 2023 at 09:47:10PM -0400, Jason Merrill wrote:
> On 5/26/23 19:18, Marek Polacek wrote:
> > Since r8-509, we'll no longer create a static temporary var for
> > the initializer '{ 1, 2 }' for num in the attached test because
> > the code in finish_compound_literal is now guarded by
> > '&& fcl_context == fcl_c99' but it's fcl_functional here. This
> > causes us to reject num as non-constant when evaluating it in
> > a template.
> >
> > Jason's idea was to treat num as value-dependent even though it
> > actually isn't. This patch implements that suggestion.
> >
> > The is_really_empty_class check is sort of non-obvious but the
> > comment should explain why I added it.
> >
> > Co-authored-by: Jason Merrill
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > PR c++/109876
> >
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (value_dependent_expression_p) : Treat a
> > constexpr-declared non-constant variable as value-dependent.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp0x/constexpr-template12.C: New test.
> > * g++.dg/cpp1z/constexpr-template1.C: New test.
> > ---
> > gcc/cp/pt.cc | 12 ++
> > .../g++.dg/cpp0x/constexpr-template12.C | 38 +++
> > .../g++.dg/cpp1z/constexpr-template1.C| 25
> > 3 files changed, 75 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
> > create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
> >
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 7fb3e75bceb..38fd8070705 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -27969,6 +27969,18 @@ value_dependent_expression_p (tree expression)
> > else if (TYPE_REF_P (TREE_TYPE (expression)))
> > /* FIXME cp_finish_decl doesn't fold reference initializers. */
> > return true;
> > + /* We have a constexpr variable and we're processing a template.
> > When
> > +there's lifetime extension involved (for which finish_compound_literal
> > +used to create a temporary), we'll not be able to evaluate the
> > +variable until instantiating, so pretend it's value-dependent. */
> > + else if (DECL_DECLARED_CONSTEXPR_P (expression)
> > + && !TREE_CONSTANT (expression)
> > + /* When there's nothing to initialize, we'll never mark the
> > + VAR_DECL TREE_CONSTANT, therefore it would remain
> > + value-dependent and we wouldn't instantiate. */
Sorry it's taken so long to get back to this.
> Interesting. Can we change that (i.e. mark it TREE_CONSTANT) rather than
> work around it here?
I think we can. Maybe as in the below:
-- >8 --
Since r8-509, we'll no longer create a static temporary var for
the initializer '{ 1, 2 }' for num in the attached test because
the code in finish_compound_literal is now guarded by
'&& fcl_context == fcl_c99' but it's fcl_functional here. This
causes us to reject num as non-constant when evaluating it in
a template.
Jason's idea was to treat num as value-dependent even though it
actually isn't. This patch implements that suggestion.
We weren't marking objects whose type is an empty class type
constant. This patch changes that so that v_d_e_p doesn't need
to check is_really_empty_class.
Co-authored-by: Jason Merrill
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/109876
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Set TREE_CONSTANT when initializing
an object of empty class type.
* pt.cc (value_dependent_expression_p) : Treat a
constexpr-declared non-constant variable as value-dependent.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-template12.C: New test.
* g++.dg/cpp1z/constexpr-template1.C: New test.
* g++.dg/cpp1z/constexpr-template2.C: New test.
---
gcc/cp/decl.cc| 13 +--
gcc/cp/pt.cc | 7
.../g++.dg/cpp0x/constexpr-template12.C | 38 +++
.../g++.dg/cpp1z/constexpr-template1.C| 25
.../g++.dg/cpp1z/constexpr-template2.C| 25
5 files changed, 105 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 60f107d50c4..792ab330dd0 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -8200,7 +8200,6 @@ void
cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
tree asmspec_tree, int flags)
{
- tree type;
vec *cleanups = NULL;
const char *asmspec = NULL;
int was_readonly = 0;
@@ -8220,7 +8219,7 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
/* Parameters are handled by store_parm_decls, not
