xlc : using clang-style warning disabling

[Baesken, Matthias]

Hello,   we recently switched to xlc16 / xlclang  in the AIX build .
( jdk11  stays on the  so-called   "legacy"  xlc 12 )

I would suggest to switch to the  clang-style  warning disabling - style now   in jdk/jdk  ( = jdk14)  to avoid some warnings in the build   .
I think we are pretty close  to  reduce the compiler warnings to 0   on AIX  , which  would make it possible to build with warnings as errors at some point in the future .

Any thoughts / comments  / opinions?


For now I would start  with those warnings disabled for hotspot :

tautological-compare  :

/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 :

/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 .



A patch is below .


Best regards, Matthias


diff -r 1b0c0af50d4e make/autoconf/flags-cflags.m4
--- a/make/autoconf/flags-cflags.m4      Wed Jul 17 15:40:27 2019 +0200
+++ b/make/autoconf/flags-cflags.m4   Thu Jul 18 13:21:24 2019 +0200
@@ -229,7 +229,7 @@
       ;;
     xlc)
-      DISABLE_WARNING_PREFIX="-qsuppress="
+      DISABLE_WARNING_PREFIX="-Wno-"
       CFLAGS_WARNINGS_ARE_ERRORS="-qhalt=w"
       # Possibly a better subset than "all" is "lan:trx:ret:zea:cmp:ret"
diff -r 1b0c0af50d4e make/hotspot/lib/CompileJvm.gmk
--- a/make/hotspot/lib/CompileJvm.gmk             Wed Jul 17 15:40:27 2019 +0200
+++ b/make/hotspot/lib/CompileJvm.gmk          Thu Jul 18 13:21:24 2019 +0200
@@ -95,8 +95,7 @@
     unknownpragma doubunder w_enumnotused w_toomanyenumnotused \
     wvarhidenmem wunreachable wnoretvalue notemsource
-DISABLED_WARNINGS_xlc := 1540-0216 1540-0198 1540-1090 1540-1639 1540-1088 \
-    1500-010
+DISABLED_WARNINGS_xlc := tautological-compare shift-negative-value
 DISABLED_WARNINGS_microsoft :=
diff -r 1b0c0af50d4e make/lib/Awt2dLibraries.gmk
--- a/make/lib/Awt2dLibraries.gmk         Wed Jul 17 15:40:27 2019 +0200
+++ b/make/lib/Awt2dLibraries.gmk     Thu Jul 18 13:21:24 2019 +0200
@@ -471,7 +471,6 @@
           $(LIBAWT_HEADLESS_CFLAGS), \
       EXTRA_HEADER_DIRS := $(LIBAWT_HEADLESS_EXTRA_HEADER_DIRS), \
       DISABLED_WARNINGS_gcc := unused-function, \
-      DISABLED_WARNINGS_xlc := 1506-356, \
       DISABLED_WARNINGS_solstudio := E_EMPTY_TRANSLATION_UNIT, \
       LDFLAGS := $(LDFLAGS_JDKLIB) \
           $(call SET_SHARED_LIBRARY_ORIGIN), \
@@ -481,10 +480,6 @@
       LIBS_solaris := $(LIBM) $(LIBDL) $(LIBCXX), \
   ))
-  # AIX warning explanation:
-  # 1506-356 : (W) Compilation unit is empty.
-  #            This happens during the headless build
-
   $(BUILD_LIBAWT_HEADLESS): $(BUILD_LIBAWT)
   TARGETS += $(BUILD_LIBAWT_HEADLESS)
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