[LLVMdev] Metadata/Value split has landed

Duncan P. N. Exon Smith dexonsmith at apple.com
Wed Dec 10 17:27:45 PST 2014 

+zalman at google.com

> On 2014 Dec 10, at 15:57, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> 
>> 
>> On 2014 Dec 10, at 14:08, Tom Stellard <tom at stellard.net> wrote:
>> 
>> On Wed, Dec 10, 2014 at 11:21:08AM -0800, Duncan P. N. Exon Smith wrote:
>>> 
>>>> On 2014 Dec 10, at 08:40, Tom Stellard <tom at stellard.net> wrote:
>>>> 
>>>> On Tue, Dec 09, 2014 at 09:22:16PM -0800, Duncan P. N. Exon Smith wrote:
>>>>> The `Metadata`/`Value` split (PR21532) landed in r223802 -- at least, the
>>>>> C++ side of it.  This was a rocky day, but I suppose that's what I get
>>>>> for failing to stage the change in smaller pieces.
>>>>> 
>>>>> As of r223916 (lldb), I'm not aware of any remaining (in-tree) breakage,
>>>>> so if I've missed some problem in the sea of buildbot errors, please
>>>>> flag me down.
>>>>> 
>>>>> I'll follow up soon with bitcode and assembly changes!
>>>> 
>>>> Hi Duncan,
>>>> 
>>>> I started getting random assertion failures in some tests yesterday, and I think
>>>> it may be related to this change.  Here is the stack trace:
>>>> 
>>>> #0  0x00007ffff59f4c39 in raise () from /lib64/libc.so.6
>>>> #1  0x00007ffff59f6348 in abort () from /lib64/libc.so.6
>>>> #2  0x00007ffff59edb96 in __assert_fail_base () from /lib64/libc.so.6
>>>> #3  0x00007ffff59edc42 in __assert_fail () from /lib64/libc.so.6
>>>> #4  0x00007ffff3a30e92 in llvm::LeakDetectorImpl<void>::addGarbage(void const*) [clone .part.19] () from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #5  0x00007ffff3a30fd3 in llvm::LeakDetector::addGarbageObjectImpl(void*) () from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #6  0x00007ffff3a40eed in llvm::MDNode::getTemporary(llvm::LLVMContext&, llvm::ArrayRef<llvm::Metadata*>) () from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #7  0x00007ffff3426b3f in MapValueImpl(llvm::Metadata const*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #8  0x00007ffff3426bd6 in MapValueImpl(llvm::Metadata const*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #9  0x00007ffff3426bd6 in MapValueImpl(llvm::Metadata const*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #10 0x00007ffff3426eed in llvm::MapValue(llvm::Metadata const*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #11 0x00007ffff3426f39 in llvm::MapValue(llvm::MDNode const*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #12 0x00007ffff3427174 in llvm::RemapInstruction(llvm::Instruction*, llvm::ValueMap<llvm::Value const*, llvm::WeakVH, llvm::ValueMapConfig<llvm::Value const*, llvm::sys::SmartMutex<false> > >&, llvm::RemapFlags, llvm::ValueMapTypeRemapper*, llvm::ValueMaterializer*) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #13 0x00007ffff3755786 in (anonymous namespace)::ModuleLinker::linkGlobalValueBody(llvm::GlobalValue&) () from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #14 0x00007ffff375767f in llvm::Linker::linkInModule(llvm::Module*) () from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #15 0x00007ffff3758cfb in llvm::Linker::LinkModules(llvm::Module*, llvm::Module*, std::function<void (llvm::DiagnosticInfo const&)>) ()
>>>> from /opt/buildbot/lib/libLLVM-3.6svn.so
>>>> #16 0x00007ffff6c9d8cf in clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) () from /opt/buildbot/lib/libOpenCL.so.1
>>>> #17 0x00007ffff6e61f23 in clang::ParseAST(clang::Sema&, bool, bool) () from /opt/buildbot/lib/libOpenCL.so.1
>>>> #18 0x00007ffff6c9e6bb in clang::CodeGenAction::ExecuteAction() () from /opt/buildbot/lib/libOpenCL.so.1
>>>> #19 0x00007ffff6b7ead6 in clang::FrontendAction::Execute() () from /opt/buildbot/lib/libOpenCL.so.1
>>>> #20 0x00007ffff6b5d179 in clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) () from /opt/buildbot/lib/libOpenCL.so.1
>>>> #21 0x00007ffff6b1282c in (anonymous namespace)::compile_llvm (llvm_ctx=..., 
>>>>  source="\n__kernel void test_fn(__local float *sSharedStorage, __global float *srcValues, __global uint *offsets, __global float *destBuffer, uint alignmentOffset )\n{\n    int tid = get_global_id( 0 );\n    sSha"..., headers=..., name="input.cl", triple="r600--", processor="verde", opts="", 
>>>>  address_spaces=..., optimization_level=@0x7fffffff21cc: 2, r_log=...) at llvm/invocation.cpp:255
>>>> #22 0x00007ffff6b140c8 in clover::compile_program_llvm (source=..., headers=..., ir=ir at entry=PIPE_SHADER_IR_NATIVE, target=..., opts=..., r_log=...)
>>>>  at llvm/invocation.cpp:710
>>>> #23 0x00007ffff6b0a371 in clover::program::build (this=this at entry=0x23a0530, devs=..., opts=opts at entry=0x7ffff793dc0d "", headers=...)
>>>>  at core/program.cpp:63
>>>> #24 0x00007ffff6af31c4 in clBuildProgram (d_prog=0x23a0538, num_devs=0, d_devs=0x0, p_opts=<optimized out>, pfn_notify=0x0, user_data=0x0)
>>>>  at api/program.cpp:182
>>>> 
>>>> Does this look related?  If so, let me know what other information you need to
>>>> try to debug this issue.
>>> 
>>> This could be related; I'm not sure.
>>> 
>> 
>> I'm pretty sure that this commit is the cause of the regression.
>> 
>> r223801 works and r223810 does not, and I don't think any of the other
>> commits in that range could cause this.
>> 
>>> It looks like a leak detection assertion, and I didn't need to change
>>> that logic at all.  `ValueMap` calls `MDNode::getTemporary()` and
>>> `MDNode::deleteTemporary()` in the same ways it used to (and I didn't
>>> touch the implementation of those).
>>> 
>>> Can you reproduce this with `llvm-link`?  If so, that sounds like the
>>> best place to start.
>> 
>> I can't reproduce this using llvm-link unfortunately.  Any other ideas?
> 
> (Continuing via email, since Tom stepped away IRC.)
> 
> Tom, from the trace [1], it the problematic pointer (0x27e4c80) only shows
> up once.
> 
> [1]: http://people.freedesktop.org/~tstellar/md-crash.out
> 
> That means that something *else* -- other than `MDNode::getTemporary()`
> -- must be adding that address to garbage and failing to remove it.
> 
> I just dug into `LeakDetector::addGarbageObject()` and it stores *all*
> calls to `addGarbage()` in the same place.  There are a fair number of
> these in the IR:
> 
> $ git grep -e addGarbageObject -w -- lib/IR/
> lib/IR/BasicBlock.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/BasicBlock.cpp:    LeakDetector::addGarbageObject(this);
> lib/IR/Function.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Function.cpp:    LeakDetector::addGarbageObject(this);
> lib/IR/Function.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Function.cpp:    LeakDetector::addGarbageObject(this);
> lib/IR/Globals.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Globals.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Globals.cpp:    LeakDetector::addGarbageObject(this);
> lib/IR/Globals.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Globals.cpp:    LeakDetector::addGarbageObject(this);
> lib/IR/Instruction.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Instruction.cpp:  LeakDetector::addGarbageObject(this);
> lib/IR/Instruction.cpp:    if (!P) LeakDetector::addGarbageObject(this);
> lib/IR/Metadata.cpp:  LeakDetector::addGarbageObject(N);
> 
> I think the next step is to identify who called `addGarbageObject()` with
> the problematic address, and what the stack trace was.
> 
> The weird thing is, I also noticed a semantic change I made here
> accidentally.  `addGarbageObject()` has two overloads: `void*` and
> `const Value*`.  `MDNode::getTemporary()` used to match the latter, but
> now it matches the former.
> 
> The weird part: all the other calls to `addGarbageObject()` look like they
> send in a `Value *`.
> 
> Do you have any other calls to `addGarbageObject()`?  Do they match
> `void *`?
> 
> Also, what happens with the attached patch?  (If this fixes your problem,
> I think it's just papering over something...)
> 
> <0001-IR-Detect-Metadata-leaks-separately-from-generic-obj.patch>

Zalman also had a reproduction, and he's been able to track it down to
an `addGarbageObject()` call from `MachineBasicBlock`.  It looks like
the MBB gets deallocated but `removeGarbageObject()` isn't called yet.

CC'ing him here so he can join the thread once he's gotten a little
further.

BTW, if this is blocking anyone, I can commit the patch I attached to
my previous email (or you can apply it locally).  I think it's probably
the right thing eventually -- it improves the output when there *is* an
issue -- but I haven't committed it yet since it'll cover up the
problem.

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