RFR: 8286562: GCC 12 reports some compiler warnings [v5]

[Kim Barrett]

On Fri, 13 May 2022 10:02:30 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> I saw some compiler warnings when I tried to build OpenJDK with GCC 12.0.1 on Fedora 36.
>> As you can see, the warnings spreads several areas. Let me know if I should separate them by area.
>> 
>> * -Wstringop-overflow
>>     * src/hotspot/share/oops/array.hpp
>>     * src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdBits.inline.hpp
>> 
>> In member function 'void Array<T>::at_put(int, const T&) [with T = unsigned char]',
>>     inlined from 'void ConstantPool::tag_at_put(int, jbyte)' at /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/constantPool.hpp:126:64,
>>     inlined from 'void ConstantPool::method_at_put(int, int, int)' at /home/ysuenaga/github-forked/jdk/src/hotspot/share/oops/constantPool.hpp:380:15,
>>     inlined from 'ConstantPool* BytecodeConstantPool::create_constant_pool(JavaThread*) const' at /home/ysuenaga/github-forked/jdk/src/hotspot/share/classfile/bytecodeAssembler.cpp:85:26:
>
> Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert change for java.c , parse_manifest.c , LinuxPackage.c

Some suggestions for code changes instead of warning suppression.  And some warnings that I don't yet understand and don't think should be suppressed without more details or investigation.

src/hotspot/share/classfile/bytecodeAssembler.cpp line 95:

> 93:         ShouldNotReachHere();
> 94:     }
> 95: PRAGMA_DIAG_POP

One of these is another of the symbol_at_put cases that I don't understand.  Are there other cases in the switch that warn?  And if so, which ones and how?  There are no details of this one in the PR cover description.

src/hotspot/share/classfile/classFileParser.cpp line 5970:

> 5968: PRAGMA_STRINGOP_OVERFLOW_IGNORED
> 5969:   _cp->symbol_at_put(hidden_index, _class_name);
> 5970: PRAGMA_DIAG_POP

I don't understand these warning suppressions for symbol_at_put (here and elsewhere).  I don't see any stringops here.  What is the compiler complaining about?  (There's no mention of classfile stuff in the review cover message.)

src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdBits.inline.hpp line 103:

> 101: PRAGMA_STRINGOP_OVERFLOW_IGNORED
> 102:   *dest = op(bits, *dest);
> 103: PRAGMA_DIAG_POP

I see no stringop here.  I'm still trying to understand what the compiler is complaining about.

src/hotspot/share/opto/memnode.cpp line 1413:

> 1411:                    bt == T_BYTE    || bt == T_SHORT ||
> 1412:                    bt == T_INT     || bt == T_LONG, "wrong type = %s", type2name(bt));
> 1413: PRAGMA_DIAG_POP

The problem here is the definition of type2name, which returns NULL for an unknown BasicType.  It would probably be better if it returned a recognizable string for that situation, eliminating this warning at it's source.

src/hotspot/share/opto/type.cpp line 4300:

> 4298: PRAGMA_FORMAT_OVERFLOW_IGNORED
> 4299:       fatal("not an element type: %s", type2name(etype));
> 4300: PRAGMA_DIAG_POP

Another occurrence of type2name returning NULL for unknown BasicType.

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Changes requested by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8646