RFR: 8293887: AArch64 build failure with GCC 12 due to maybe-uninitialized warning in libfdlibm k_rem_pio2.c [v2]

[Magnus Ihse Bursie]

On Mon, 26 Sep 2022 01:39:41 GMT, Hao Sun <haosun at openjdk.org> wrote:

>> This warning seems to be a false positive, because 1) array "fq" with elements from index 0 to "jz" has already been initialized as "fw" at line 290 [1], and 2) variable "jz" should be non-negative from the comment at line 99 [2].
>> 
>> Note-1: GCC warning option -Wmaybe-uninitialized is not a new one. Note-2: x86-64 build with GCC 12 on Ubuntu 22.04 passed in my local test.
>> 
>> This warning is raised only on GCC 12 + AArch64. I suspect it might be some GCC 12 bug, so I reported it to GCC community [3].
>> 
>> Since it involves third party code, I think it's better to suppress the warning by simply disabling this warning option in the makefile.
>> 
>> Testing: Release builds with GCC 9, GCC 11 and GCC 12 passed on Ubuntu 22.04/AArch64 system.
>> 
>> [1] https://github.com/openjdk/jdk/blob/master/src/java.base/share/native/libfdlibm/k_rem_pio2.c#L290 
>> [2] https://github.com/openjdk/jdk/blob/master/src/java.base/share/native/libfdlibm/k_rem_pio2.c#L99 
>> [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106992
>
> Hao Sun has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Disable the warning option per file
>    
>    After JDK-8294281, we can disable the warning options per file.
>    
>    Testing: Release builds with GCC 9, GCC 11 and GCC 12 passed on Ubuntu
>    22.04/AArch64 system.
>  - Merge branch 'master' into 8293887-gcc12-fdlibm
>  - 8293887: AArch64 build failure with GCC 12 due to maybe-uninitialized warning in libfdlibm k_rem_pio2.c
>    
>    This warning seems to be a false positive, because 1) array "fq" with
>    elements from index 0 to "jz" has already been initialized as "fw" at
>    line 290 [1], and 2) variable "jz" should be non-negative from the
>    comment at line 99 [2].
>    
>    Note-1: GCC warning option -Wmaybe-uninitialized is not a new one.
>    Note-2: x86-64 build with GCC 12 on Ubuntu 22.04 passed in my local
>    test.
>    
>    This warning is raised only on GCC 12 + AArch64. I suspect it might be
>    some GCC 12 bug, so I reported it to GCC community [3].
>    
>    Since it involves third party code, I think it's better to suppress the
>    warning by simply disabling this warning option in the makefile.
>    
>    Testing: Release builds with GCC 9, GCC 11 and GCC 12 passed on Ubuntu
>    22.04/AArch64 system.
>    
>    [1] https://github.com/openjdk/jdk/blob/master/src/java.base/share/native/libfdlibm/k_rem_pio2.c#L290
>    [2] https://github.com/openjdk/jdk/blob/master/src/java.base/share/native/libfdlibm/k_rem_pio2.c#L99
>    [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106992

LGTM

-------------

Marked as reviewed by ihse (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10386