RFR: 8228426: xlc: switch to clang-style warning disabling

[Doerr, Martin]

Hi Matthias,

looks good to me. I think this makes sense for jdk14 where we only support xlclang++ on AIX.

Best regards,
Martin


> -----Original Message-----
> From: build-dev <build-dev-bounces at openjdk.java.net> On Behalf Of
> Baesken, Matthias
> Sent: Montag, 22. Juli 2019 12:03
> To: Baesken, Matthias <matthias.baesken at sap.com>; 'build-
> dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'ppc-aix-port-
> dev at openjdk.java.net' <ppc-aix-port-dev at openjdk.java.net>
> Subject: RE: RFR: 8228426: xlc: switch to clang-style warning
> disabling
> 
> Hello, any comments please ?
> 
> From: ppc-aix-port-dev <ppc-aix-port-dev-bounces at openjdk.java.net> On
> Behalf Of Baesken, Matthias
> Sent: Freitag, 19. Juli 2019 12:20
> To: 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>; 'ppc-aix-
> port-dev at openjdk.java.net' <ppc-aix-port-dev at openjdk.java.net>
> Subject: [CAUTION] RFR: 8228426: xlc: switch to clang-style warning disabling
> 
> Please review the following change that switches to  clang-style warning
> disabling  on AIX,  and  adjusts the warning  disabling to current needs .
> 
> Recently the jdk/jdk build on AIX switched to xlc16/xlclang.
> 
> This means we can now use the standard clang-style warning disabling (the
> old legacy qsuppress warning disablings from legacy xlc
> might not fully work any more).
> 
> I think we are pretty close in reducing the compiler warnings to 0 on AIX,
> which would make it possible to build with warnings as errors at some point
> in the future .
> 
> In a first step I would disable these warnings in HS for xlc16/xlclang :
> 
> tautological-compare : (seen in os_aix.cpp)
> 
> /jdk/src/hotspot/os/aix/os_aix.cpp:2400:15: warning: comparison of
> unsigned expression >= 0 is always true [-Wtautological-compare]
>     if (bytes >= Use64KPagesThreshold) {
>         ~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
> /jdk/src/hotspot/os/aix/os_aix.cpp:2607:15: warning: comparison of
> unsigned expression >= 0 is always true [-Wtautological-compare]
>     if (bytes >= Use64KPagesThreshold) {
> 
> In the product  build   the   "Use64KPagesThreshold"   is a constant  so clang
> complains .  However  in the  (fast)debug  builds one can set
> Use64KPagesThreshold  with an -XX setting.
> So I think it is best to disable the warning.
> 
> 
> shift-negative-value : (seen in c1_LIRGenerator_ppc.cpp)
> 
> /jdk/src/hotspot/cpu/ppc/c1_LIRGenerator_ppc.cpp:429:97: warning:
> shifting a negative signed value is undefined [-Wshift-negative-value]
>       (x->op() == Bytecodes::_lsub && right.value()->type()-
> >as_LongConstant()->value() == ((-1)<<15)) ) {
>                                                                                             ~~~~^
> /jdk/src/hotspot/cpu/ppc/c1_LIRGenerator_ppc.cpp:483:96: warning:
> shifting a negative signed value is undefined [-Wshift-negative-value]
>       (x->op() == Bytecodes::_isub && right.value()->type()->as_IntConstant()-
> >value() == ((-1)<<15)) ) {
> 
> We could probably replace  the -1 shift by a constant but I think it  is nicely
> readable .
> 
> 
> 
> Bug/webrev :
> 
> https://bugs.openjdk.java.net/browse/JDK-8228426
> 
> http://cr.openjdk.java.net/~mbaesken/webrevs/8228426.0/
> 
> 
> Thanks, Matthias