[PATCH] Make CloneFunction also clone debug info metadata

[David Blaikie]

Patches 1 & 2 look fine - can you commit them, or do you need me to?

(I'm rather surprised only one test had trouble with this (though I expect
there's a bunch of LLVM tests that all have these {i32 0} in them that I'll
clean up when I remove the bits of code that silently handle this case) -
but awesome... shows how cargo culty some things can be I guess)


On Thu, Jan 30, 2014 at 1:58 AM, Alon Mishne <alonmishne at gmail.com> wrote:

> OK, so I've prepared 3 patches:
>
> 1. LLVM patch changing DIBuilder
> 2. Clang patch changing the test
> 3. LLVM patch changing the clone functionality and its tests
>
> Patches (1) and (2) should be submitted together, and (3) later.
>
> If you think the other conditionals you mentioned should be fixed in
> patches (1) or (2) above, I'd appreciate some help - either you change them
> or at least give me pointers on where to look :-)
>
> - Alon
>
>
> On 29 January 2014 19:41, David Blaikie <dblaikie at gmail.com> wrote:
>
>> Thanks Alon for following up.
>>
>> Could you pull out the change to make those {i32 0} -> {} into a separate
>> patch? It'd be good to review/commit that (and maybe remove a bunch of
>> those conditionals I was mentioning) separately. Including updating the
>> relevant Clang test.
>>
>> To answer your question, yes, I think it's fine to change the [[EMPTY]]
>> thing to {} rather than {i32 0}. I believe it was some kind of legacy (I'd
>> /love/ to know what the original reason was just to satisfy myself that it
>> no longer (or never) holds, but I'm not sure I'll ever know for sure).
>>
>>
>> On Wed, Jan 29, 2014 at 12:48 AM, Alon Mishne <alonmishne at gmail.com>wrote:
>>
>>> Update to address David's comments:
>>>
>>> 1. Added tests to verify dbg.declare and dbg.value are cloned as
>>> expected.
>>> 2. Ran the Clang tests... and indeed, one test failed:
>>> debug-info-template.cpp. The test has a check that expects "metadata !{i32
>>> 0}" where "metadata !{}" now appears. Changing this check allows the test
>>> to pass. It's not quite clear to me whether that's okay, though - David, I
>>> saw you're the one who added that check - is it okay to modify it?
>>>
>>> Also CC to Eric (Nadav suggested you might be interested)
>>>
>>> - Alon
>>>
>>>
>>> On 2 January 2014 21:28, Alon Mishne <alonmishne at gmail.com> wrote:
>>>
>>>> Thanks for the quick reply - see responses below.
>>>>
>>>>
>>>>> *From:* dblaikie at gmail.com [mailto:dblaikie at gmail.com]
>>>>> *Sent:* Thursday, January 02, 2014 20:08
>>>>>
>>>>> Thanks for working on this.
>>>>>
>>>>
>>>>
>>>> I hate to do this to you - but did you run the Clang tests after your
>>>>> change to DIBuilder? DIBuilder is, unfortunately, not tested by LLVM's
>>>>> tests - but is indirectly tested by Clang's debug info IRGen level tests.
>>>>>
>>>>
>>>> Didn't run them, thanks for pointing this out, will do so.
>>>>
>>>> I'd be more than happy to remove that weird zero-length arrays are
>>>>> emitted as arrays with a single zero. I assumed there was an IR limitation
>>>>> (that we couldn't have zero-length metadata values) that created this
>>>>> situation, but I never went to look/verify that that was actually the case.
>>>>>
>>>>
>>>>
>>>> (we can remove a bunch of conditionals that can just become asserts if
>>>>> we can remove that zero/one/i32 0 array encoding weirdness)
>>>>>
>>>>
>>>>
>>>> If it passes Clang's tests, it's probably worth committing that change
>>>>> separately.
>>>>>
>>>>
>>>> You mean that the DIBuilder modification should be committed first
>>>> separately, before the rest of this patch?
>>>>
>>>>
>>>>> The loop that adds the new subprogram to the CUs' subprogram lists
>>>>> could probably just bail out once it finds a single copy - that list
>>>>> shouldn't contain duplicates.
>>>>>
>>>>
>>>> That's exactly what I thought, but then Michael Kuperstein showed me
>>>> that it actually can happen: if you have two compilation units that were
>>>> linked together and each contained the same function definition (possible
>>>> with "linkonce_odr", for example), then you'll indeed get two subprogram
>>>> entries pointing to the *same* function, linked from the two different CUs.
>>>>
>>>> I'd have to think more about whether what you've done is sufficient for
>>>>> the duplication. I have a sneaking suspicion that it isn't - what happens
>>>>> to the dbg_declare/dbg_value intrinsics in the cloned function? What
>>>>> variables do they point to? what context do those variables point to? (I
>>>>> suspect they point back to the original, not the cloned, function, which
>>>>> could be problematic)
>>>>>
>>>>>
>>>>
>>>> It's a good point, I'll add unit tests to check it - and if they fail
>>>> will also fix the code.
>>>>
>>>> Thanks again for the thorough review!
>>>>
>>>> - Alon
>>>>
>>>> On Thu Jan 02 2014 at 7:47:28 AM, Mishne, Alon <alon.mishne at intel.com>
>>>>> wrote:
>>>>> Right now CloneFunction ignores the debug info metadata, which can
>>>>> lead to debug info loss when the cloned function is used. This patch
>>>>> modifies that so that if the 'ModuleLevelChanges' parameter to
>>>>> CloneFunction is true, any debug info metadata for the old function is
>>>>> cloned for the new function.
>>>>>
>>>>> Also expanded the cloning unit tests to test for this new
>>>>> functionality.
>>>>>
>>>>> Additionally, one of my tests required checking for an empty DIArray,
>>>>> but apparently DIBuilder doesn't make those - if asked to create an empty
>>>>> array, it creates an array with a single "null" value instead. I've changed
>>>>> DIBuilder to no longer do that because I don't understand why it's done and
>>>>> all the tests still pass after the change.
>>>>
>>>>
>>>
>>
>
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