[Bug middle-end/64101] GCC considers that the erf math function does not set errno

[niva at niisi dot msk.ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64101

--- Comment #2 from niva at niisi dot msk.ru ---
Please explain why erf is marked as 'const' and
does not use ATTR_MATHFN_FPROUNDING_ERRNO? 
ISO C does not say that erf may not set errno. 
And POSIX directly requires that erf, erff, erfl 
set errno=ERANGE in case of underflow.

Here is another example:

#include <stdio.h>
#include <errno.h>
#include <math.h>

extern double res;
int main ()
{
   errno = 0;
   res = erf (-1.2553634935946022721708238314E-308);
   printf ("errno=%d, res=%g\n", errno, res);
   return 0;
}

As a result of

    mips64-none-elf-gcc -O1 -S tst2_erf.c -o tst2_erf.s

the following code is generated:

main:
    ...
    addiu    $sp,$sp,-40
    sd    $31,32($sp)
    sw    $0,%gp_rel(errno)($28)
    jal    erf
    ldc1    $f12,%gp_rel($LC0)($28)

    sdc1    $f0,%gp_rel(res)($28)
    lui    $4,%hi($LC1)    # printf arg 0: format line
    addiu    $4,$4,%lo($LC1)
    dmfc1    $6,$f0        # printf arg 2: res
    jal    printf
    move    $5,$0        #! printf arg 1: zero (must be errno)

    move    $2,$0
    ld    $31,32($sp)
    j    $31
    addiu    $sp,$sp,40

Zero ($0) is passed to printf instead of errno.
If -fno-builtin-printf is used the compiler generates

    lw    $5,%gp_rel(errno)($28)

instead of 

    move    $5,$0

in the delay slot after "jal  printf".





В Птн, 28/11/2014 в 13:24 +0000, rguenth at gcc dot gnu.org пишет:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64101
> 
> Richard Biener <rguenth at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Target|                            |x86_64-*-*, mips64-none-elf
>              Status|UNCONFIRMED                 |NEW
>    Last reconfirmed|                            |2014-11-28
>      Ever confirmed|0                           |1
> 
> --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
> I think the issue is that you don't use the result of erf() and the function
> is marked as 'const' - thus does not use ATTR_MATHFN_FPROUNDING_ERRNO.
> If you make 'res' global then it will work.
>