RFR: 8365312: GCC 12 cannot compile SVE on aarch64 with auto-var-init pattern [v2]

[Fei Gao]

On Thu, 14 Aug 2025 09:43:12 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> make/autoconf/flags-cflags.m4 line 960:
>> 
>>> 958:             # avoids the use of unsupported `__builtin_clear_padding` for variable
>>> 959:             # length aggregates
>>> 960:             if test "x$TOOLCHAIN_TYPE" = xgcc ; then
>> 
>> We only add `-ftrival-auto-var-init=pattern` when "x$DEBUG_LEVEL" != "xrelease", e.g. only in
>> debug builds.  I think we should only add the `=zero` flag in debug builds and nothing in release
>> builds here too.
>
> I agree. Make sure to use the same test (DEBUG_LEVEL != release) to catch both fast and slow debug builds.

That does make sense. Updated in the new commit. Thanks! @magicus @kimbarrett

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PR Review Comment: https://git.openjdk.org/jdk/pull/26755#discussion_r2279071503