[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |przemoc at gmail dot com

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2010-11-29 19:37:32 UTC ---
*** Bug 46711 has been marked as a duplicate of this bug. ***

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-03-28 06:57:56 UTC ---
*** Bug 56759 has been marked as a duplicate of this bug. ***

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-03-28 08:53:54 UTC ---
Created attachment 29742
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29742
gcc49-pr19449.patch

Untested patch.  There is another case where we'd better fold
__builtin_constant_p right away, for static/extern function-local array
dimensions:
int y;
static char a[__builtin_constant_p (y) ? -1 : 1];
extern char b[__builtin_constant_p (y) ? -1 : 1];
char d[__builtin_constant_p (y) ? -1 : 1];

void
foo (int x)
{
  static char e[__builtin_constant_p (x) ? -1 : 1];
  extern char f[__builtin_constant_p (x) ? -1 : 1];
  auto char g[__builtin_constant_p (x) ? -1 : 1];
  char h[__builtin_constant_p (x) ? -1 : 1];
}

Right now this compiles fine for -O0, but for -O1 and above it errors on e and
f (twice on the latter actually).  When cfun == NULL, we always fold
__builtin_constant_p right away, but when cfun is NULL, we don't consider
static/extern.  Not sure how to fix this issue though, because I think the
declspecs aren't passed down to declarator parsing.

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-03 10:00:19 UTC ---
Author: jakub
Date: Wed Apr  3 09:17:44 2013
New Revision: 197393

URL: http://gcc.gnu.org/viewcvs?rev=197393&root=gcc&view=rev
Log:
    PR c/19449
    * tree.h (force_folding_builtin_constant_p): New decl.
    * builtins.c (force_folding_builtin_constant_p): New variable.
    (fold_builtin_constant_p): Fold immediately also if
    force_folding_builtin_constant_p.

    * c-parser.c (c_parser_get_builtin_args): Add choose_expr_p
    argument.  If set, or it temporarily for parsing of the first
    argument into force_folding_builtin_constant_p.
    (c_parser_postfix_expression): Adjust callers.

    * gcc.c-torture/execute/pr19449.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr19449.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/builtins.c
    trunk/gcc/c/ChangeLog
    trunk/gcc/c/c-parser.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree.h

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[desrt at desrt dot ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

Ryan Lortie <desrt at desrt dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |desrt at desrt dot ca

--- Comment #7 from Ryan Lortie <desrt at desrt dot ca> ---
Another case, and this one fails at all optimisation levels:

int a(void) { return 0; }

/* This always returns a constant expression.  If we can't statically
 * determine its value, then this is the constant expression '0'.
 */
#define CONSTIFY(x) (__builtin_constant_p(x)&&(x))

/* works fine */
int b = CONSTIFY(a());
int c = CONSTIFY(a()) ? 2 : 3;

/* fails */
int d = __builtin_choose_expr(CONSTIFY(a()), 2, 3);

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2005-12-18 01:38:34         |2021-2-10
      Known to fail|                            |11.0, 3.4.2
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #8 from Martin Sebor <msebor at gcc dot gnu.org> ---
No change in GCC 11:

$ gcc -O -S -Wall pr19449.c
pr19449.c: In function ‘foo’:
pr19449.c:9:15: error: storage size of ‘e’ isn’t constant
    9 |   static char e[__builtin_constant_p (x) ? -1 : 1];
      |               ^
pr19449.c:10:15: error: object with variably modified type must have no linkage
   10 |   extern char f[__builtin_constant_p (x) ? -1 : 1];
      |               ^
pr19449.c:10:15: error: storage size of ‘f’ isn’t constant
pr19449.c:12:8: warning: unused variable ‘h’ [-Wunused-variable]
   12 |   char h[__builtin_constant_p (x) ? -1 : 1];
      |        ^
pr19449.c:11:13: warning: unused variable ‘g’ [-Wunused-variable]
   11 |   auto char g[__builtin_constant_p (x) ? -1 : 1];
      |             ^
pr19449.c:10:15: warning: unused variable ‘f’ [-Wunused-variable]
   10 |   extern char f[__builtin_constant_p (x) ? -1 : 1];
      |               ^
pr19449.c:9:15: warning: unused variable ‘e’ [-Wunused-variable]
    9 |   static char e[__builtin_constant_p (x) ? -1 : 1];
      |               ^
At top level:
pr19449.c:2:13: warning: ‘a’ defined but not used [-Wunused-variable]
    2 | static char a[__builtin_constant_p (y) ? -1 : 1];
      |             ^

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-01-14 19:26 -------
The problem is the __builtin_constant_p is delayed for evalutation until optimizations are run but 
__builtin_choose_expr needs an answer right away.


What we could do is for when processing the first argument of __builtin_choose_expr, say we are not in 
a function.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
  GCC build triplet|i686-pc-cygwin              |
   GCC host triplet|i686-pc-cygwin              |
 GCC target triplet|arm-unknown-elf             |
           Keywords|                            |rejects-valid
   Last reconfirmed|0000-00-00 00:00:00         |2005-01-14 19:26:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[eplondke at gmail dot com]

------- Additional Comments From eplondke at gmail dot com  2005-01-14 19:22 -------
Created an attachment (id=7961)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7961&action=view)
Test case as a file.

Test case as a file.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449

[Bug c/19449] __builtin_constant_p cannot resolve to const when optimizing

[ian at airs dot com]

-- 
           What    |Removed                     |Added
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                 CC|                            |ian at airs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449