RFR: JDK-8306304: Fix xlc17 clang warnings in ppc and aix code [v2]

[Kim Barrett]

On Mon, 15 May 2023 09:30:52 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> /data/d042520/xlc17/jdk/src/hotspot/cpu/ppc/c1_LIRGenerator_ppc.cpp:426:97: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
>> I reverted my change in c1_LIRGenerator_ppc.cpp and added shift-negative-value to the DISABLED_WARNINGS_clang in CompileJvm.gmk.
>> 
>> ad_ppc.cpp:18388:10: error: converting the result of '?:' with integer constants to a boolean always evaluates to 'true' [-Werror,-Wtautological-constant-compare]
>>   assert(VerifyOops || MachNode::size(ra_) <= VM_Version::has_brw() ? 16 : 20, "bad fixed size");
>>          ^
>> Should I also add tautological-constant-compare to DISABLED_WARNINGS_clang in CompileJvm.gmk or where else?
>
> I see, so `size` is kind of macro-like, and is just textually splicing its argument expression into another expression.
> And without the added parens the resulting full expression for the assert isn't checking what's intended, due
> to operator precedence.
> 
> This is in generated source; it might be better to find the code generator (somewhere in adlc) and change it
> to add appropriate parens, as there may be other similar places (both here and for other platforms) that
> aren't doing what's intended but are not triggering warnings.

Such a fix of adlc is probably out of scope for this change though.  We should probably have a separate bug for that.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13953#discussion_r1193581173