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

22 Jul 2019

      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@openjdk.java.net> On Behalf Of
Baesken, Matthias
Sent: Montag, 22. Juli 2019 12:03
To: Baesken, Matthias <matthias.baesken@sap.com>; 'build-
dev@openjdk.java.net' <build-dev@openjdk.java.net>; 'ppc-aix-port-
dev@openjdk.java.net' <ppc-aix-port-dev@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@openjdk.java.net> On
Behalf Of Baesken, Matthias
Sent: Freitag, 19. Juli 2019 12:20
To: 'build-dev@openjdk.java.net' <build-dev@openjdk.java.net>; 'ppc-aix-
port-dev@openjdk.java.net' <ppc-aix-port-dev@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

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

Doerr, Martin