Warnings Cleanup in Hotspot
Jeremy Manson
jeremymanson at google.com
Fri May 17 10:32:06 PDT 2013
I wonder why that didn't pop up when I compiled it.
I disagree with David. Casting to void is the accepted strategy for
getting rid of unused value warnings. It makes perfect sense to me; if you
cast to void, it isn't a value anymore. It's also good documentation: it
says you know you aren't using the value, and that that is not a mistake.
I did it several times in my patch.
Furthermore, turning on the warning will prevent mistakes like the strcmp /
strcpy one I fixed in my patch. It seems worth it to have a few scattered
(void) casts in the VM.
Jeremy
On Thu, May 16, 2013 at 6:59 PM, David Holmes <david.holmes at oracle.com>wrote:
> Calvin,
>
>
> On 17/05/2013 4:55 AM, Calvin Cheung wrote:
>
>> Jeremy,
>>
>> It seems your suggested patch is incomplete as the build on linux was
>> failing.
>> Recall that warnings are treated as errors as in gcc.make:
>> # Compiler warnings are treated as errors
>> WARNINGS_ARE_ERRORS = -Werror
>>
>> Below is the list of files I needed to change for the build to go
>> through on linux:
>> make/linux/makefiles/gcc.make
>> src/share/vm/c1/c1_IR.cpp
>> src/share/vm/ci/ciUtilities.**hpp
>> src/share/vm/classfile/**genericSignatures.cpp
>> src/share/vm/classfile/**verifier.hpp
>> src/share/vm/code/nmethod.cpp
>> src/share/vm/memory/**cardTableModRefBS.cpp
>> src/share/vm/memory/universe.**cpp
>> src/share/vm/oops/**constantPool.cpp
>> src/share/vm/prims/forte.cpp
>> src/share/vm/runtime/perfData.**hpp
>> src/share/vm/runtime/**sharedRuntime.cpp
>> src/share/vm/services/**diagnosticArgument.cpp
>> src/share/vm/utilities/**exceptions.hpp
>> src/share/vm/utilities/**taskqueue.hpp
>>
>> Most of the warnings are related to: "statement has no effect"
>> e.g. in exceptions.hpp, I needed to change
>> #define CHECK THREAD); if
>> (HAS_PENDING_EXCEPTION) return ; (0
>> to
>> #define CHECK THREAD); if
>> (HAS_PENDING_EXCEPTION) return ; (void)(0
>>
>> I don't want to share webrev yet since I haven't built on other
>> platforms and haven't done any testing on the change.
>>
>> 2 ways I'm thinking of fixing it:
>> 1) include the -Wunused-value warning flag
>> this means changes are required on the files listed above
>>
>> 2) not include the -Wunused-value warning flag but only fixing the
>> potential coding errors which would impact functionality as you pointed
>> out in your email. This should result in a smaller changeset.
>>
>
> I think I prefer #2 mainly because:
>
> 0;
>
> and
>
> (void)0;
>
> are equally bereft of any effect so I don't see why the compiler complains
> about one and accepts the other. As this seems completely arbitrary
> different compilers may have different views, or change their view over
> time. So I suggest not changing this and only fix the real issues that
> -Wunused-value produces.
>
> Just my 2c.
>
> David
> ------
>
>
> Calvin
>>
>> On 5/16/2013 10:55 AM, Jeremy Manson wrote:
>>
>>> Okay. Is there anything you want me to do?
>>>
>>> Jeremy
>>>
>>>
>>> On Wed, May 15, 2013 at 2:37 PM, Calvin Cheung
>>> <calvin.cheung at oracle.com <mailto:calvin.cheung at oracle.**com<calvin.cheung at oracle.com>>>
>>> wrote:
>>>
>>> Jeremy,
>>>
>>> We'll fix it in hs25 first and then backport it to hs24 if the fix
>>> is applicable there.
>>>
>>> Calvin
>>>
>>>
>>> On 5/15/2013 2:14 PM, Jeremy Manson wrote:
>>>
>>>> Thanks, Calvin. What does followup look like?
>>>>
>>>> Jeremy
>>>>
>>>>
>>>> On Mon, May 13, 2013 at 9:59 AM, Calvin Cheung
>>>> <calvin.cheung at oracle.com <mailto:calvin.cheung at oracle.**com<calvin.cheung at oracle.com>>>
>>>> wrote:
>>>>
>>>> Hi Jeremy,
>>>>
>>>> I've created 8014431 (cleanup warnings indicated by the
>>>> -Wunused-value compiler option on linux) to track this. It'll
>>>> take a few hours for it to show up in the bugs.sun.com
>>>> <http://bugs.sun.com>
>>>> http://bugs.sun.com/**bugdatabase/view_bug.do?bug_**id=8014431<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8014431>
>>>>
>>>> Calvin
>>>>
>>>>
>>>> On 5/10/2013 11:38 AM, Jeremy Manson wrote:
>>>>
>>>> Okay, I turned on -Wunused-value in the gcc makefile for
>>>> Linux. I also ran this on a more recent build of HS (I
>>>> was using something very, very old), and I got a few more
>>>> warnings (including a couple that actually looked as if
>>>> they would impact functionality). Thoughts on this?
>>>>
>>>> diff --git a/make/linux/makefiles/gcc.**make
>>>> b/make/linux/makefiles/gcc.**make
>>>> --- a/make/linux/makefiles/gcc.**make
>>>> +++ b/make/linux/makefiles/gcc.**make
>>>> @@ -126,7 +126,7 @@
>>>> # Compiler warnings are treated as errors
>>>> WARNINGS_ARE_ERRORS = -Werror
>>>> -WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
>>>> -Wunused-function
>>>> +WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
>>>> -Wunused-function -Wunused-value
>>>> # Since GCC 4.3, -Wconversion has changed its meanings
>>>> to warn these implicit
>>>> # conversions which might affect the values. Only enable
>>>> it in earlier versions.
>>>> diff --git a/src/share/vm/c1/c1_IR.cpp
>>>> b/src/share/vm/c1/c1_IR.cpp
>>>> --- a/src/share/vm/c1/c1_IR.cpp
>>>> +++ b/src/share/vm/c1/c1_IR.cpp
>>>> @@ -506,7 +506,7 @@
>>>> _loop_map(0, 0), // initialized later with
>>>> correct size
>>>> _compilation(c)
>>>> {
>>>> - TRACE_LINEAR_SCAN(2, "***** computing linear-scan
>>>> block order");
>>>> + TRACE_LINEAR_SCAN(2, tty->print_cr("***** computing
>>>> linear-scan block order"));
>>>> init_visited();
>>>> count_edges(start_block, NULL);
>>>> @@ -683,7 +683,7 @@
>>>> }
>>>> void
>>>> ComputeLinearScanOrder::**assign_loop_depth(BlockBegin*
>>>> start_block) {
>>>> - TRACE_LINEAR_SCAN(3, "----- computing loop-depth and
>>>> weight");
>>>> + TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing
>>>> loop-depth and weight"));
>>>> init_visited();
>>>> assert(_work_list.is_empty(), "work list must be empty
>>>> before processing");
>>>> @@ -868,7 +868,7 @@
>>>> }
>>>> void ComputeLinearScanOrder::**compute_order(BlockBegin*
>>>> start_block) {
>>>> - TRACE_LINEAR_SCAN(3, "----- computing final block
>>>> order");
>>>> + TRACE_LINEAR_SCAN(3, tty->print_cr("----- computing
>>>> final block order"));
>>>> // the start block is always the first block in the
>>>> linear scan order
>>>> _linear_scan_order = new BlockList(_num_blocks);
>>>> diff --git a/src/share/vm/code/nmethod.**cpp
>>>> b/src/share/vm/code/nmethod.**cpp
>>>> --- a/src/share/vm/code/nmethod.**cpp
>>>> +++ b/src/share/vm/code/nmethod.**cpp
>>>> @@ -2602,7 +2602,8 @@
>>>> relocation_begin()-1+ip[1]);
>>>> for (; ip < index_end; ip++)
>>>> tty->print_cr(" (%d ?)", ip[0]);
>>>> - tty->print_cr(" @" INTPTR_FORMAT ":
>>>> index_size=%d", ip, *ip++);
>>>> + tty->print_cr(" @" INTPTR_FORMAT ":
>>>> index_size=%d", ip, *ip);
>>>> + ip++;
>>>> tty->print_cr("reloc_end @" INTPTR_FORMAT ":", ip);
>>>> }
>>>> }
>>>> diff --git a/src/share/vm/memory/**cardTableModRefBS.cpp
>>>> b/src/share/vm/memory/**cardTableModRefBS.cpp
>>>> --- a/src/share/vm/memory/**cardTableModRefBS.cpp
>>>> +++ b/src/share/vm/memory/**cardTableModRefBS.cpp
>>>> @@ -395,7 +395,7 @@
>>>> }
>>>> // Touch the last card of the covered region to show
>>>> that it
>>>> // is committed (or SEGV).
>>>> - debug_only(*byte_for(_covered[**ind].last());)
>>>> + debug_only((void) (*byte_for(_covered[ind].last(**)));)
>>>> debug_only(verify_guard();)
>>>> }
>>>> diff --git a/src/share/vm/memory/**universe.cpp
>>>> b/src/share/vm/memory/**universe.cpp
>>>> --- a/src/share/vm/memory/**universe.cpp
>>>> +++ b/src/share/vm/memory/**universe.cpp
>>>> @@ -532,7 +532,9 @@
>>>> if (vt) vt->initialize_vtable(false, CHECK);
>>>> if (ko->oop_is_instance()) {
>>>> InstanceKlass* ik = (InstanceKlass*)ko;
>>>> - for (KlassHandle s_h(THREAD, ik->subklass()); s_h()
>>>> != NULL; s_h = (THREAD, s_h()->next_sibling())) {
>>>> + for (KlassHandle s_h(THREAD, ik->subklass());
>>>> + s_h() != NULL;
>>>> + s_h = KlassHandle(THREAD, s_h()->next_sibling()))
>>>> {
>>>> reinitialize_vtable_of(s_h, CHECK);
>>>> }
>>>> }
>>>> diff --git a/src/share/vm/runtime/**sharedRuntime.cpp
>>>> b/src/share/vm/runtime/**sharedRuntime.cpp
>>>> --- a/src/share/vm/runtime/**sharedRuntime.cpp
>>>> +++ b/src/share/vm/runtime/**sharedRuntime.cpp
>>>> @@ -2733,7 +2733,7 @@
>>>> // ResourceObject, so do not put any ResourceMarks in
>>>> here.
>>>> char *s = sig->as_C_string();
>>>> int len = (int)strlen(s);
>>>> - *s++; len--; // Skip opening paren
>>>> + s++; len--; // Skip opening paren
>>>> char *t = s+len;
>>>> while( *(--t) != ')' ) ; // Find close paren
>>>> diff --git a/src/share/vm/services/**diagnosticArgument.cpp
>>>> b/src/share/vm/services/**diagnosticArgument.cpp
>>>> --- a/src/share/vm/services/**diagnosticArgument.cpp
>>>> +++ b/src/share/vm/services/**diagnosticArgument.cpp
>>>> @@ -232,7 +232,7 @@
>>>> } else {
>>>> _value._time = 0;
>>>> _value._nanotime = 0;
>>>> - strcmp(_value._unit, "ns");
>>>> + strcpy(_value._unit, "ns");
>>>> }
>>>> }
>>>> diff --git a/src/share/vm/utilities/**taskqueue.hpp
>>>> b/src/share/vm/utilities/**taskqueue.hpp
>>>> --- a/src/share/vm/utilities/**taskqueue.hpp
>>>> +++ b/src/share/vm/utilities/**taskqueue.hpp
>>>> @@ -340,8 +340,12 @@
>>>> if (dirty_n_elems == N - 1) {
>>>> // Actually means 0, so do the push.
>>>> uint localBot = _bottom;
>>>> - // g++ complains if the volatile result of the
>>>> assignment is unused.
>>>> - const_cast<E&>(_elems[**localBot] = t);
>>>> + // g++ complains if the volatile result of the
>>>> assignment is
>>>> + // unused, so we cast the volatile away. We cannot
>>>> cast directly
>>>> + // to void, because gcc treats that as not using the
>>>> result of the
>>>> + // assignment. However, casting to E& means that we
>>>> trigger an
>>>> + // unused-value warning. So, we cast the E& to void.
>>>> + (void) const_cast<E&>(_elems[**localBot] = t);
>>>> OrderAccess::release_store(&_**bottom,
>>>> increment_index(localBot));
>>>> TASKQUEUE_STATS_ONLY(stats.**record_push());
>>>> return true;
>>>> @@ -397,7 +401,12 @@
>>>> return false;
>>>> }
>>>> - const_cast<E&>(t = _elems[oldAge.top()]);
>>>> + // g++ complains if the volatile result of the
>>>> assignment is
>>>> + // unused, so we cast the volatile away. We cannot
>>>> cast directly
>>>> + // to void, because gcc treats that as not using the
>>>> result of the
>>>> + // assignment. However, casting to E& means that we
>>>> trigger an
>>>> + // unused-value warning. So, we cast the E& to void.
>>>> + (void) const_cast<E&>(t = _elems[oldAge.top()]);
>>>> Age newAge(oldAge);
>>>> newAge.increment();
>>>> Age resAge = _age.cmpxchg(newAge, oldAge);
>>>> @@ -640,8 +649,12 @@
>>>> uint dirty_n_elems = dirty_size(localBot, top);
>>>> assert(dirty_n_elems < N, "n_elems out of range.");
>>>> if (dirty_n_elems < max_elems()) {
>>>> - // g++ complains if the volatile result of the
>>>> assignment is unused.
>>>> - const_cast<E&>(_elems[**localBot] = t);
>>>> + // g++ complains if the volatile result of the
>>>> assignment is
>>>> + // unused, so we cast the volatile away. We cannot
>>>> cast directly
>>>> + // to void, because gcc treats that as not using the
>>>> result of the
>>>> + // assignment. However, casting to E& means that we
>>>> trigger an
>>>> + // unused-value warning. So, we cast the E& to void.
>>>> + (void) const_cast<E&>(_elems[**localBot] = t);
>>>> OrderAccess::release_store(&_**bottom,
>>>> increment_index(localBot));
>>>> TASKQUEUE_STATS_ONLY(stats.**record_push());
>>>> return true;
>>>> @@ -665,7 +678,12 @@
>>>> // This is necessary to prevent any read below from
>>>> being reordered
>>>> // before the store just above.
>>>> OrderAccess::fence();
>>>> - const_cast<E&>(t = _elems[localBot]);
>>>> + // g++ complains if the volatile result of the
>>>> assignment is
>>>> + // unused, so we cast the volatile away. We cannot
>>>> cast directly
>>>> + // to void, because gcc treats that as not using the
>>>> result of the
>>>> + // assignment. However, casting to E& means that we
>>>> trigger an
>>>> + // unused-value warning. So, we cast the E& to void.
>>>> + (void) const_cast<E&>(t = _elems[localBot]);
>>>> // This is a second read of "age"; the "size()" above
>>>> is the first.
>>>> // If there's still at least one element in the queue,
>>>> based on the
>>>> // "_bottom" and "age" we've read, then there can be
>>>> no interference with
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
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