Warnings Cleanup in Hotspot
Jeremy Manson
jeremymanson at google.com
Mon May 20 12:46:40 PDT 2013
Calvin,
Do you want to take this over, or should I generate a new patch? I note
that there are a couple of other places I missed (all of which seem to have
the same pattern of (0)).
Jeremy
On Fri, May 17, 2013 at 4:18 PM, Jeremy Manson <jeremymanson at google.com>wrote:
> Nice catch - I guess before, that was expanding to
>
> bool match = compare_entry_to(k1, cp2, k2, THREAD);
> if (HAS_PENDING_EXCEPTION) return false;
> (0) && compare_operand_to(i1, cp2, i2, THREAD);
> if (HAS_PENDING_EXCEPTION) return false;
> (0);
>
> which is perfectly legal, but booogus...
>
> Jeremy
>
>
>
>
> On Fri, May 17, 2013 at 3:08 PM, Calvin Cheung <calvin.cheung at oracle.com>wrote:
>
>> On 5/17/2013 10:32 AM, Jeremy Manson wrote:
>>
>> I wonder why that didn't pop up when I compiled it.
>>
>> I cloned my repo from the following:
>> http://hg.openjdk.java.net/hsx/hotspot-rt/hotspot
>>
>> g++ version is 4.4.6
>>
>> The file list I mentioned was for fastdebug build on linux_x64.
>> When I switched to product build, I found couple more files need to be
>> changed.
>> Then I needed to change more files for the 32-bit build.
>> So there will be few more files added to the list.
>>
>>
>> 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.
>>
>> After adding the (void) cast in CHECK_false, I'm seeing the following
>> error:
>> constantPool.cpp:1067: error: void value not ignored as it ought to be
>> 1066 bool match = compare_entry_to(k1, cp2, k2, CHECK_false) &&
>> 1067 compare_operand_to(i1, cp2, i2, CHECK_false);
>> 1068 return match;
>>
>> the way I fixed it is to break up 1066 - 1067 into 2 statements such as
>> follows:
>> 1066 bool match_entry = compare_entry_to(k1, cp2, k2, CHECK_false);
>> 1067 bool match_operand = compare_operand_to(i1, cp2, i2,
>> CHECK_false);
>> 1068 return (match_entry && match_operand);
>>
>> Calvin
>>
>>
>> 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>> 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>>
>>>>>> 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
>>>>>>
>>>>>> 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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