[Bug c++/107358] New: [13 Regression] i686-linux: Since r13-3290-g98e341130f8798 code fails to build libjxl-0/7.0 (vector float code)

["slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107358

            Bug ID: 107358
           Summary: [13 Regression] i686-linux: Since
                    r13-3290-g98e341130f8798 code fails to build
                    libjxl-0/7.0 (vector float code)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org, jakub at redhat dot com
  Target Milestone: ---

Initially observed build failure on libjxl-0.7.0 on i686-linux target.

Seems to happen only on i686-unknown-linux-gnu and only on -std=c++11.

PR107295 does not seem to be enough to fix it. Here is the minimal example:

// $ cat skcms.cc
// this works:
float approx_scal(float e) {
    return e - 124.225514990f;
}

typedef float __attribute__((vector_size(4*sizeof(float)))) F;

// this fails:
//   error: conversion of scalar 'long double' to vector 'F' {aka '__vector(4)
float'} involves truncation
F approx_vec(F e) {
    return e - 124.225514990f;
    //return e - 1.0f; // this works, does 'f' get ignored when float does not
fit?
}


$ g++-13 -fPIC -std=c++11 -o skcms.cc.o -c skcms.cc
skcms.cc: In function 'F approx_vec(F)':
skcms.cc:10:17: warning: SSE vector return without SSE enabled changes the ABI
[-Wpsabi]
   10 | F approx_vec(F e) {
      |                 ^
skcms.cc:11:14: error: conversion of scalar 'long double' to vector 'F' {aka
'__vector(4) float'} involves truncation
   11 |     return e - 124.225514990f;
      |            ~~^~~~~~~~~~~~~~~~

$ g++-12 -fPIC -std=c++11 -o skcms.cc.o -c skcms.cc
skcms.cc: In function 'F approx_vec(F)':
skcms.cc:10:17: warning: SSE vector return without SSE enabled changes the ABI
[-Wpsabi]
   10 | F approx_vec(F e) {
      |                 ^
skcms.cc:10:3: note: the ABI for passing parameters with 16-byte alignment has
changed in GCC 4.6
   10 | F approx_vec(F e) {
      |   ^~~~~~~~~~
skcms.cc:10:3: warning: SSE vector argument without SSE enabled changes the ABI 

Note: gcc-12 works, gcc-13 fails.