[Bug testsuite/114568] [14 regression] g++.dg/vect/pr84556.cc fails to produce executable since r14-9706-gb8e7aaaf350a45

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114568

--- Comment #5 from Maxim Kuvyrkov <mkuvyrkov at gcc dot gnu.org> ---
Looking at this problem more, I think the issue is due to ARM target trying
hard to avoid UNSUPPORTED tests, instead of embracing them.

For the vectorization NEON check we have ...
===
proc check_effective_target_arm_neon_ok_nocache { } {
    global et_arm_neon_flags
    set et_arm_neon_flags ""
    if { [check_effective_target_arm32] } {
        foreach flags {"" "-mfloat-abi=softfp" "-mfpu=neon" "-mfpu=neon
-mfloat-abi=softfp" "-mfpu=neon -mfloat-abi=softfp -march=armv7-a"
"-mfloat-abi=hard" "-mfpu=neon -mfloat-abi=hard" "-mfpu=neon -mfloat-abi=hard
-march=armv7-a"} {
            if { [check_no_compiler_messages_nocache arm_neon_ok object {
                #include <arm_neon.h>
...
===
... where target tries to find a set of flags compatible with _any_ of the
built multilibs to run the testsuite.

I think this is excessive, since each multilib should be tested on its own
merits, and if armv7-m does not support vectorization, there should be no
effort to try and switch to armv7-a or armv8-m+mve multilib in order to run
vectorization tests.  In other words, vectorization tests should be marked
UNSUPPORTED in armv7-m, and PASS/FAIL in armv7-a and/or armv8-m+mve.

In practical terms, my proposed solution to this problem is to remove all
"foreach flags" options except for the default "".

ARM maintainers, what am I missing?