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

[Baesken, Matthias]

Thanks for the review !
May I have a second reviewer please?

Best regards, Matthias

> -----Original Message-----
> From: Doerr, Martin
> Sent: Montag, 22. Juli 2019 12:43
> To: Baesken, Matthias <matthias.baesken at sap.com>; 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
> 
> 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