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)