[r16-5628 Regression] FAIL: g++.target/i386/vect-pragma-target-2.C -std=gnu++20 (test for excess errors) on Linux/x86_64

On Linux/x86_64,

004438857554f47eb5491d59b067e56fdacf0e74 is the first bad commit
commit 004438857554f47eb5491d59b067e56fdacf0e74
Author: Jakub Jelinek <[email protected]>
Date:   Wed Nov 26 15:01:11 2025 +0100

    Change the default C++ dialect to gnu++20

caused

FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 10)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 11)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 12)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 13)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 14)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 15)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 4)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 5)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 6)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 7)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 8)
FAIL: g++.target/i386/mv28.C  -std=c++20  (test for errors, line 9)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 10)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 11)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 12)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 13)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 14)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 15)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 4)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 5)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 6)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 7)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 8)
FAIL: g++.target/i386/mv28.C  -std=c++26  (test for errors, line 9)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 10)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 11)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 12)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 13)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 14)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 15)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 4)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 5)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 6)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 7)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 8)
FAIL: g++.target/i386/mv28.C  -std=c++98  (test for errors, line 9)
FAIL: g++.target/i386/pr82625.C  -std=gnu++20  scan-tree-dump-times optimized "return 4096;" 1
FAIL: g++.target/i386/pr82625.C  -std=gnu++20  scan-tree-dump-times optimized "return 8192;" 1
FAIL: g++.target/i386/pr82625.C  -std=gnu++26  scan-tree-dump-times optimized "return 4096;" 1
FAIL: g++.target/i386/pr82625.C  -std=gnu++26  scan-tree-dump-times optimized "return 8192;" 1
FAIL: g++.target/i386/pr82625.C  -std=gnu++98  scan-tree-dump-times optimized "return 4096;" 1
FAIL: g++.target/i386/pr82625.C  -std=gnu++98  scan-tree-dump-times optimized "return 8192;" 1
FAIL: g++.target/i386/vect-pragma-target-1.C  -std=gnu++20  scan-assembler-times vpaddw.+zmm[0-9]+ 1
FAIL: g++.target/i386/vect-pragma-target-1.C  -std=gnu++26  scan-assembler-times vpaddw.+zmm[0-9]+ 1
FAIL: g++.target/i386/vect-pragma-target-1.C  -std=gnu++98  scan-assembler-times vpaddw.+zmm[0-9]+ 1

with GCC configured with

../../gcc/configure --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-5628/usr --enable-clocale=gnu --with-system-zlib --with-demangler-in-ld --with-fpmath=sse --enable-languages=c,c++,fortran --enable-cet --without-isl --enable-libmpx x86_64-linux --disable-bootstrap

To reproduce:

$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/mv28.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/mv28.C --target_board='unix{-m64\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/pr82625.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/pr82625.C --target_board='unix{-m64\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/vect-pragma-target-1.C --target_board='unix{-m32\ -march=cascadelake}'"
$ cd {build_dir}/gcc && make check RUNTESTFLAGS="i386.exp=g++.target/i386/vect-pragma-target-1.C --target_board='unix{-m64\ -march=cascadelake}'"

(Please directly reply to this email for question about this report.)
(If you met problems with cascadelake related, disabling AVX512F in command line might save that.)
(However, please make sure that there is no potential problems with AVX512.)