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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/113835] [13/14 Regression] compiling std::vector with
 const size in C++20 is slow
Date: Fri, 09 Feb 2024 06:58:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113835

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-02-09
   Target Milestone|---                         |13.3
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |13.2.1, 14.0
          Component|c++                         |libstdc++
      Known to work|                            |12.2.1
            Summary|compiling std::vector with  |[13/14 Regression]
                   |const size in C++20 is slow |compiling std::vector with
                   |                            |const size in C++20 is slow

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed with -std=3Dc++20 -fsyntax-only

 constant expression evaluation     :   1.80 ( 85%)   0.03 ( 14%)   1.84 ( =
78%)
  220M ( 88%)
 TOTAL                              :   2.13          0.22          2.36=20=
=20=20=20=20=20=20
  250M


Samples: 8K of event 'cycles', Event count (approx.): 9294971478=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20
Overhead       Samples  Command  Shared Object     Symbol=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  16.33%          1385  cc1plus  cc1plus           [.]
cxx_eval_constant_expression
   4.35%           369  cc1plus  cc1plus           [.] cxx_eval_call_expres=
sion
   3.90%           331  cc1plus  cc1plus           [.]
cxx_eval_store_expression
   3.16%           268  cc1plus  cc1plus           [.]
hash_table<hash_map<tree_node*, tree_node*, simple_has
   2.55%           216  cc1plus  cc1plus           [.]
hash_table<hash_map<tree_node*, tree_node*, simple_has
   2.15%           183  cc1plus  cc1plus           [.] ggc_internal_alloc
   2.04%           173  cc1plus  cc1plus           [.]
hash_table<int_cst_hasher, false, xcallocator>::find_s
   1.98%           168  cc1plus  cc1plus           [.] tree_operand_check

GCC 12 was fast (possibly std::vector wasn't constexpr there?)=