[Bug c++/104620] New: FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[Bug c++/104620] New: FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[danglin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

            Bug ID: 104620
           Summary: FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20
                    (test for errors)
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: danglin at gcc dot gnu.org
  Target Milestone: ---
              Host: hppa*-*-linux*
            Target: hppa*-*-linux*
             Build: hppa*-*-linux*

AIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 80)
FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 84)

spawn -ignore SIGHUP /home/dave/gnu/gcc/objdir/gcc/testsuite/g++/../../xg++
-B/h
ome/dave/gnu/gcc/objdir/gcc/testsuite/g++/../../
/home/dave/gnu/gcc/gcc/gcc/test
suite/g++.dg/cpp23/consteval-if2.C -fdiagnostics-plain-output -nostdinc++
-I/hom
e/dave/gnu/gcc/objdir/hppa-linux-gnu/libstdc++-v3/include/hppa-linux-gnu
-I/home
/dave/gnu/gcc/objdir/hppa-linux-gnu/libstdc++-v3/include
-I/home/dave/gnu/gcc/gc
c/libstdc++-v3/libsupc++ -I/home/dave/gnu/gcc/gcc/libstdc++-v3/include/backward
-I/home/dave/gnu/gcc/gcc/libstdc++-v3/testsuite/util -fmessage-length=0
-std=gnu
++20 -S -o consteval-if2.s
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C: In function
'
constexpr bool f()':
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:7:6: warning:
'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exten
sions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:7:22: error:
e
xpected ';' before '{' token
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:7:6: error:
'i
f consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:10:10:
warning
: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-ext
ensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:10:27: error:
expected ';' before '{' token
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:10:10: error:
'if consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:13:6:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:13:6: error:
'
if consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:15:8:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:15:21: error:
'if consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:17:6:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:17:19: error:
'if consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:20:8:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:23:5: error:
'
if consteval' requires compound statement
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C: In function
'
constexpr int baz(int)':
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:34:10:
warning
: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-ext
ensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:36:16: error:
'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:42:6:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:48:16: error:
'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:50:8:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:52:16: error:
'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:54:6:
warning:
 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-exte
nsions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C: In function
'constexpr int qux(int)':
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:66:10:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:68:16: error:
'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:74:6:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:82:8:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:86:6:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C: In function
'constexpr T corge(T)':
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:98:10:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:106:6:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:114:8:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:118:6:
warning: 'if consteval' only available with '-std=c++2b' or '-std=gnu++2b'
[-Wc++23-extensions]
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C: In
instantiation of 'constexpr T corge(T) [with T = int]':
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:128:16:  
required from here
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:100:16:
error: 'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:112:16:
error: 'x' is not a constant expression
/home/dave/gnu/gcc/gcc/gcc/testsuite/g++.dg/cpp23/consteval-if2.C:116:16:
error: 'x' is not a constant expression
compiler exited with status 1
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 7)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 8 (test for errors,
line 7)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 9 (test for warnings,
line 7)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 10)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 11 (test for errors,
line 10)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 12 (test for
warnings, line 10)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 13)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 14 (test for
warnings, line 13)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 15)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 16 (test for
warnings, line 15)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 17)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  at line 18 (test for
warnings, line 17)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 20)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 23)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 34)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 36)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 42)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 48)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 50)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 52)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 54)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 66)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 68)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 74)
FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 80)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 82)
FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 84)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 86)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 98)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 100)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 106)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 112)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 114)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 116)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for warnings, line 118)
PASS: g++.dg/cpp23/consteval-if2.C  -std=gnu++20 (test for excess errors)

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|hppa*-*-linux*              |
                 CC|                            |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-03-23
             Status|UNCONFIRMED                 |NEW
             Target|hppa*-*-linux*              |
              Build|hppa*-*-linux*              |

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I see it on x86_64 too.  Confirmed.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 80)
FAIL: g++.dg/cpp23/consteval-if2.C  -std=gnu++20  (test for errors, line 84)

After r12-7264-gc19f317a78c0e4 these two errors only show up with -fchecking=2.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
   Target Milestone|---                         |12.0
                 CC|                            |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Reduced testcase for -std=c++23
consteval int foo (int x) { return x; }
consteval int bar () { return 2; }

template <typename T>
constexpr int
qux (int x)
{
  int r = 0;
  if consteval
    {
      r += 2 * bar ();
    }
  else
    {
      r += foo (8 * x); // { dg-error "is not a constant expression" }
    }
  if ! consteval
    {
      r += foo (32 * x);// { dg-error "is not a constant expression" }
    }
  if consteval
    {
      r += 32 * bar ();
    }
  return r;
}

The intent of the testcase was to test whether we catch at least some of the
non-dependent consteval calls already during template parsing and so regardless
of whether we actually instantiate them or not.
Worst case it will be diagnosed during instantiation, sure.
But x is not type nor value dependent and neither is 8 * x nor 32 * x.
And make_args_non_dependent calls build_non_dependent_arg which will not wrap
say x or 8, but does wrap x * 8 even when both arguments have integral types.
So, either build_non_dependent_arg should be made smarter and not wrap even
simple arithmetics etc. where no C++ template-ish trees appear inside of it and
everything is like in normal non-template-ish code, or we should reconsider
the r12-7264 case because clearly often we can handle NON_DEPENDENT_EXPR just
fine.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Another testcase to consider is:
consteval int foo (int x) { return x; }
consteval int bar () { return 2; }
constexpr int baz (int x) { return x; }

template <typename T>
constexpr int
qux (int x)
{
  int r = 0;
  if consteval          // { dg-warning "'if consteval' only available with" ""
{ target c++20_only } }
    {
      r += 2 * bar ();
    }
  else
    {
      r += foo (8 * baz (0));
    }
  if ! consteval        // { dg-warning "'if consteval' only available with" ""
{ target c++20_only } }
    {
      r += foo (32 * baz (0));
    }
  if consteval          // { dg-warning "'if consteval' only available with" ""
{ target c++20_only } }
    {
      r += 32 * bar ();
    }
  return r;
}

This one is valid, but before your r12-7264 was incorrectly rejected because 8
* baz (0) etc. is wrapped in NON_DEPENDENT_EXPR,
potential_constant_expression_1 recursed on the NON_DEPENDENT_EXPR operand,
found it is ok but cxx_eval_constant_expression
rejected the NON_DEPENDENT_EXPR.  Bet for the build_over_call
processing_template_decl immediate_invocation_p code we need to punt silently
if there is something we can't handle but fail loudly if we can handle
everything but it is clearly always not a constant expression. 
potential_constant_expression_1 isn't 100% accurate, there are cases where it
gets stuff through.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Some context: consider the simplified/extended C++20 testcase (the consteval-if
seems to be a red herring):

consteval int foo(int x) { return x; }

template<class>
void bar(int x)
{
  constexpr int y = 0;
  foo(8 * x); // #1
  foo(8 * y); // #2
}

Before r12-7264, we would indeed correctly reject #1 ahead of time (which has a
non-constant arg), but we would also incorrectly reject #2 (which has a
constant arg), because both arguments are wrapped in NON_DEPENDENT_EXPR which
cxx_eval_constant_expr considers to be always non-constant.  So essentially we
used to reject the two now-failing tests in consteval-if2.C only by accident.

After r12-7264, is_constant_expr returns false for NON_DEPENDENT_EXPR
(mirroring cxx_eval_constant_expr) which in particular means that
fold_non_dependent_expr no longer tries to check a non-dependent consteval call
ahead of time if it has a "complex" argument (i.e. one that is wrapped in
NON_DEPENDENT_EXPR).  Thus we no longer reject #1 ahead of time, and we also no
longer incorrectly reject #2.  IMHO this is overall an improvement, since not
rejecting #1 ahead of time is a QoI issue, whereas rejecting #2 is a
correctness issue.  This also fixed PR103443 for a similar reason.

(In reply to Jakub Jelinek from comment #3)
> So, either build_non_dependent_arg should be made smarter and not wrap even
> simple arithmetics etc. where no C++ template-ish trees appear inside of it
> and everything is like in normal non-template-ish code, or we should
> reconsider
> the r12-7264 case because clearly often we can handle NON_DEPENDENT_EXPR
> just fine.

I wonder if we can get rid of NON_DEPENDENT_EXPR entirely?  I'm not sure if
it's at all necessary anymore.  Or perhaps we could change tsubst /
is_constant_expr / eval_constant_expr to actually look through
NON_DEPENDENT_EXPR.  These ideas seem out of scope for GCC 12 though :/

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
The reason that the two tests in constexpr-if2.C don't fail with -fchecking=2
after r12-7264 seems to be a latent bug.  The error comes from the call to
fold_non_dependent_expr in build_non_dependent_expr (which is guarded by
flag_checking > 1), despite passing complain=tf_none.  I think build_over_call
needs to use cxx_constant_value_sfinae instead of cxx_constant_value when
evaluating a consteval call...  I have a patch for this.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> This one is valid, but before your r12-7264 was incorrectly rejected because
> 8 * baz (0) etc. is wrapped in NON_DEPENDENT_EXPR,
> potential_constant_expression_1 recursed on the NON_DEPENDENT_EXPR operand,
> found it is ok but cxx_eval_constant_expression
> rejected the NON_DEPENDENT_EXPR.

Makes sense, similar to the #2 case in comment #5.

> Bet for the build_over_call
> processing_template_decl immediate_invocation_p code we need to punt
> silently if there is something we can't handle but fail loudly if we can
> handle everything but it is clearly always not a constant expression. 
> potential_constant_expression_1 isn't 100% accurate, there are cases where
> it gets stuff through.

IIUC as long as NON_DEPENDENT_EXPR doesn't appear inside a non-dependent
consteval call then we'll currently correctly accept/reject it ahead of time,
e.g.:

consteval int foo(int x) { return x; }

template<class>
void bar(int x)
{
  constexpr int y = 0;
  foo(x);     // error: 'x' is not a constant expression
  foo(y);     // OK
  foo(x * 1); // no (ahead of time) error due to NON_DEPENDENT_EXPR
}

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #7)
> IIUC as long as NON_DEPENDENT_EXPR doesn't appear inside a non-dependent
> consteval call then we'll currently correctly accept/reject it ahead of
> time, e.g.:

Right.  The problem we're hitting is that within a template we're trying to
evaluate the immediate invocation inside build_over_call rather than when we
return to e.g. finish_call_expr and build up the call to actually go into the
template trees: if we fold_non_dependent_expr at that point instead, it should
be fine.  The only problem with that is that there are a bunch of places that
need to be changed.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:647537adefb34041cc2d44585252fd765cc0daae

commit r12-7802-g647537adefb34041cc2d44585252fd765cc0daae
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Mar 24 11:42:31 2022 -0400

    c++: missing SFINAE for non-constant consteval calls [PR104620]

    Here we weren't respecting SFINAE when evaluating a call to a consteval
    function, which caused us to reject the new testcase below.  This patch
    fixes this by making build_over_call use the SFINAE-friendly version of
    cxx_constant_value.

    This change causes us to no longer diagnose ahead of time a couple of
    non-constant non-dependent consteval calls in consteval-if2.C with
    -fchecking=2.  These errors were apparently coming from the call to
    fold_non_dependent_expr in build_non_dependent_expr (for the RHS of the +=)
    despite complain=tf_none being passed.  Now that build_over_call respects
    the value of complain during constant evaluation of a consteval call,
    the errors are gone.

    That the errors are also gone without -fchecking=2 is a regression caused
    by r12-7264-gc19f317a78c0e4 and is the subject of PR104620.  As described
    in comment #5, I think it's basically an accident that we were diagnosing
    these two calls correctly before r12-7264, so perhaps we can live without
    these errors for GCC 12.  Thus this patch just XFAILs the two tests.

            PR c++/104620

    gcc/cp/ChangeLog:

            * call.cc (build_over_call): Use cxx_constant_value_sfinae
            instead of cxx_constant_value to evaluate a consteval call.
            * constexpr.cc (cxx_constant_value_sfinae): Add decl parameter
            and pass it to cxx_eval_outermost_constant_expr.
            * cp-tree.h (cxx_constant_value_sfinae): Add decl parameter.
            * pt.cc (fold_targs_r): Pass NULL_TREE as decl parameter to
            cxx_constant_value_sfinae.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/consteval-if2.C: XFAIL two dg-error tests where
            the argument to the non-constant non-dependent consteval call is
            wrapped by NON_DEPENDENT_EXPR.
            * g++.dg/cpp2a/consteval30.C: New test.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #8)
> (In reply to Patrick Palka from comment #7)
> > IIUC as long as NON_DEPENDENT_EXPR doesn't appear inside a non-dependent
> > consteval call then we'll currently correctly accept/reject it ahead of
> > time, e.g.:
> 
> Right.  The problem we're hitting is that within a template we're trying to
> evaluate the immediate invocation inside build_over_call rather than when we
> return to e.g. finish_call_expr and build up the call to actually go into
> the template trees: if we fold_non_dependent_expr at that point instead, it
> should be fine.  The only problem with that is that there are a bunch of
> places that need to be changed.

That'd work for finish_call_expr and build_new_method call since they're given
the original arguments, but other callers e.g. build_new_op never see the
original arguments, so we wouldn't be able to do fold_non_dependent_expr from
there IIUC.  For build_new_op in particular, we'd have to instead
fold_non_dependent_expr from _its_ callers, the build_x_* class of functions, I
think..

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #10)
> That'd work for finish_call_expr and build_new_method call since they're
> given the original arguments, but other callers e.g. build_new_op never see
> the original arguments, so we wouldn't be able to do fold_non_dependent_expr
> from there IIUC.  For build_new_op in particular, we'd have to instead
> fold_non_dependent_expr from _its_ callers, the build_x_* class of
> functions, I think..

Agreed.  Or possibly reorganize them to share the non-dep handling between them
better.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.0                        |12.2

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 12.1 is being released, retargeting bugs to GCC 12.2.

[Bug c++/104620] FAIL: g++.dg/cpp23/consteval-if2.C -std=gnu++20 (test for errors)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104620

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.3                        |12.4

--- Comment #14 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.