[Bug c/101985] New: vec_cpsgn parameter order

["simb611alt at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101985

            Bug ID: 101985
           Summary: vec_cpsgn parameter order
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simb611alt at gmail dot com
  Target Milestone: ---

I have found an issue where the parameter order of the vec_cpsgn function on
POWER is reversed. Clang has recently fixed the same issue in their code which
leaves only GCC using the reversed order.
XLC always used the order clang currently uses.

Patch link for clang -
https://github.com/llvm/llvm-project/commit/1af037f643fc5499f83d92e5aec199950871d475

Link to POWER documentation -
http://cdn.openpowerfoundation.org/wp-content/uploads/resources/Intrinsics-Reference/content/VIPR.reference.vecfns.html

#include <stdio.h>
#include <altivec.h>

int main() {
    vector float a = {  1,  2, - 3, - 4};
    vector float b = {-10, 20, -30,  40};

    a = vec_cpsgn(a, b);
    printf("%f %f %f %f\n", a[0], a[1], a[2], a[3]);
    return 0;
}

Output for GCC 11.0.1:
-1.000000 2.000000 -3.000000 4.000000

Output for clang 12.0.1:
10.000000 20.000000 -30.000000 -40.000000

Output for xlc 16.1.1:
10.000000 20.000000 -30.000000 -40.000000