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From: "eggert at gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/99591] New: Improving __builtin_add_overflow performance on x86-64 Date: Mon, 15 Mar 2021 08:46:29 +0000 [thread overview] Message-ID: <bug-99591-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99591 Bug ID: 99591 Summary: Improving __builtin_add_overflow performance on x86-64 Product: gcc Version: 10.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: eggert at gnu dot org Target Milestone: --- This is with gcc (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9) on x86-64. For the function: _Bool signed1_overflow (signed char a, signed char b) { signed char r; return __builtin_add_overflow (a, b, &r); } gcc generates the code: signed1_overflow: movsbl %sil, %esi movsbl %dil, %edi addb %sil, %dil seto %al ret The movsbl instructions are unnecessary and can be omitted. For the function: _Bool signed2_overflow (short a, short b) { short r; return __builtin_add_overflow (a, b, &r); } gcc generates: signed2_overflow: movswl %di, %edi movswl %si, %esi xorl %eax, %eax addw %si, %di jo .L8 .L6: andl $1, %eax ret .L8: movl $1, %eax jmp .L6 Better would be this: signed2_overflow: addw %si, %di seto %al retq There are similar opportunities for improvement in __builtin_sub_overflow and __builtin_mul_overflow. This bug report follows up on this discussion about Gnulib: https://lists.gnu.org/r/bug-gnulib/2021-03/msg00078.html https://lists.gnu.org/r/bug-gnulib/2021-03/msg00079.html https://lists.gnu.org/r/bug-gnulib/2021-03/msg00080.html
next reply other threads:[~2021-03-15 8:46 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-15 8:46 eggert at gnu dot org [this message] 2021-09-01 5:30 ` [Bug target/99591] " pinskia at gcc dot gnu.org 2021-09-01 5:32 ` pinskia at gcc dot gnu.org 2021-09-01 7:44 ` eggert at cs dot ucla.edu 2021-09-01 7:57 ` [Bug c/99591] " pinskia at gcc dot gnu.org 2021-09-01 8:16 ` jakub at gcc dot gnu.org 2021-09-01 8:53 ` [Bug tree-optimization/99591] " jakub at gcc dot gnu.org 2021-09-02 9:26 ` cvs-commit at gcc dot gnu.org 2021-09-02 9:29 ` jakub at gcc dot gnu.org
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