[jira] Updated: (STDCXX-335) std::min() suboptimal

["Martin Sebor (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/STDCXX-335?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Martin Sebor updated STDCXX-335:
--------------------------------

    Fix Version/s: 4.3

Not sure we'll be able to do anything about this w/o the blessing of the committee since changing the signature of the function would be easily detectable even for fundamental types. See the test case below. Scheduled for 4.3.

#include <cassert>
#include <algorithm>

int main ()
{
    int x = 0;
    int y = 2;
    const int &z = std::min (x, y);

    x = 1;

    assert (&z == &x);
    assert (z == 1);
}


> std::min() suboptimal
> ---------------------
>
>                 Key: STDCXX-335
>                 URL: https://issues.apache.org/jira/browse/STDCXX-335
>             Project: C++ Standard Library
>          Issue Type: Bug
>          Components: 25. Algorithms
>    Affects Versions: 4.1.3
>         Environment: gcc 3.2.3, x86 Linux
>            Reporter: Mark Brown
>             Fix For: 4.3
>
>
> I don't know if it's the compiler that's generating worse code for the stdcxx version of min or if the function is not implemented as efficiently as it could be but the disassembly for the two functions below shows that my_min() is one instruction shorter than test_min():
> #include <algorithm>
> int test_min (int x, int y) { return std::min (x, y); }
> int my_min (int x, int y) { return x < y ? x : y; }
> _Z8test_minii:
>         pushl   %ebp
>         movl    %esp, %ebp
>         movl    12(%ebp), %eax
>         cmpl    %eax, 8(%ebp)
>         jg      .L2
>         leal    8(%ebp), %eax   <<< extra load?
> .L4:
>         movl    (%eax), %eax
>         leave
>         ret
> _Z6my_minii:
>         pushl   %ebp
>         movl    %esp, %ebp
>         movl    12(%ebp), %eax
>         cmpl    8(%ebp), %eax
>         jle     .L6
>         movl    8(%ebp), %eax
> .L6:
>         leave
>         ret

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