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From: "david at westcontrol dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/100890] New: The "div" standard library functions could be
 optimised as builtins
Date: Thu, 03 Jun 2021 07:01:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100890

            Bug ID: 100890
           Summary: The "div" standard library functions could be
                    optimised as builtins
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david at westcontrol dot com
  Target Milestone: ---

The C standard library has a family of functions for calculating the divisi=
on
and remainder as a pair - "div", "ldiv", "lldiv", "imaxdiv".  These could be
optimised by the compiler using inline code, in the same manner as many oth=
er
library functions such as the "abs" family (listed under "Other builtins" in
the manual).

For example, "div" can be implemented as:

div_t div(int a, int b) {
    div_t d;
    d.quot =3D a / b;
    d.rem =3D a % b;
    return d;
}

Inlining this in place of a call to "div" results in code that is smaller a=
nd
faster on most targets, as well as providing far more optimisation
opportunities (constant propagation, re-arranging with other code, etc.).=