[llvm-dev] [RFC][ThinLTO] llvm-dis ThinLTO summary dump format
Charles Saternos via llvm-dev
llvm-dev at lists.llvm.org
Thu Jun 8 16:16:36 PDT 2017
Hey Teresa,
I've updated the YAML to include the names and GUIDs for all
functions/global vars/aliases. I've also added the hotness info to the
output, but for some reason, none of my tests when running with FDO gave
anything besides Unknown. I'll be looking more into this tomorrow.
Here's the current format:
> ../build/bin/llvm-lto2 dump-summary b.o
---
NamedGlobalValueMap:
:
- GUID: 3762489268811518743
Kind: GlobalVar
Linkage: PrivateLinkage
NotEligibleToImport: true
Live: false
cold:
- GUID: 11668175513417606517
Kind: Function
Linkage: ExternalLinkage
NotEligibleToImport: true
Live: false
InstCount: 5
Calls:
- Name: puts
GUID: 8979701042202144121
Hotness: Unknown
fib:
- GUID: 8667248078361406812
Kind: Function
Linkage: ExternalLinkage
NotEligibleToImport: true
Live: false
InstCount: 26
Calls:
- Name: fib
GUID: 8667248078361406812
Hotness: Unknown
hot:
- GUID: 10177652421713147431
Kind: Function
Linkage: ExternalLinkage
NotEligibleToImport: true
Live: false
InstCount: 14
Calls:
- Name: fib
GUID: 8667248078361406812
Hotness: Unknown
- Name: printf
GUID: 7383291119112528047
Hotness: Unknown
llvm.used:
- GUID: 15665353970260777610
Kind: GlobalVar
Linkage: AppendingLinkage
NotEligibleToImport: true
Live: true
TypeIdMap:
WithGlobalValueDeadStripping: false
...
Thanks,
Charles
On Wed, Jun 7, 2017 at 12:38 PM, Teresa Johnson <tejohnson at google.com>
wrote:
>
>
> On Wed, Jun 7, 2017 at 8:58 AM, Charles Saternos <
> charles.saternos at gmail.com> wrote:
>
>> Alright, now it outputs YAML in the following format:
>>
>> ---
>> NamedGlobalValueMap:
>> X:
>> - Kind: GlobalVar
>> Linkage: ExternalLinkage
>> NotEligibleToImport: false
>> Live: false
>> a:
>> - Kind: Alias
>> Linkage: WeakAnyLinkage
>> NotEligibleToImport: false
>> Live: false
>> AliaseeGUID: 1881667236089500162
>> afun:
>> - Kind: Function
>> Linkage: ExternalLinkage
>> NotEligibleToImport: false
>> Live: false
>> InstCount: 2
>> testtest:
>> - Kind: Function
>> Linkage: ExternalLinkage
>> NotEligibleToImport: false
>> Live: false
>> InstCount: 2
>> Calls:
>> - Function: 14471680721094503013
>> TypeIdMap:
>> WithGlobalValueDeadStripping: false
>> ...
>>
>> Any thoughts on the new format?
>>
>
> Thanks, Charles. The main improvement I think we would want is to output
> value names instead of the GUID. Can you build up a map from GUID -> name
> ahead of time and use those like you were for your initial patch? Actually,
> I also think it would be useful to emit both the GUID and the name, since
> the combined index will eventually only have the GUID, so this would give a
> mapping to use for at least the visual inspection of the combined index.
>
> Also, would be good to see an example with FDO, to make sure the hotness
> info of the calls is emitted.
>
> Teresa
>
>
>> Thanks,
>> Charles
>>
>> On Tue, Jun 6, 2017 at 5:21 PM, Mehdi AMINI <joker.eph at gmail.com> wrote:
>>
>>>
>>>
>>> 2017-06-06 13:38 GMT-07:00 David Blaikie <dblaikie at gmail.com>:
>>>
>>>>
>>>>
>>>> On Tue, Jun 6, 2017 at 1:26 PM Mehdi AMINI <joker.eph at gmail.com> wrote:
>>>>
>>>>> 2017-06-05 14:27 GMT-07:00 David Blaikie via llvm-dev <
>>>>> llvm-dev at lists.llvm.org>:
>>>>>
>>>>>> I know there's been a bunch of discussion here already, but I was
>>>>>> wondering if perhaps someone (probably Teresa? Peter?) could:
>>>>>>
>>>>>> 1) summarize the current state
>>>>>> 2) describe the end-goal
>>>>>> 3) describe what steps (& how this patch relates) are planned to get
>>>>>> to (2)
>>>>>>
>>>>>> My naive thoughts, not being intimately familiar with any of this:
>>>>>> Usually bitcode and textual IR support go in together or around the same
>>>>>> time, and designed that way from the start (take r211920 for examaple,
>>>>>> which added an explicit representation of COMDATs to the IR). This seems to
>>>>>> have been an oversight in the implementation of IR summaries (is that an
>>>>>> accurate representation/statement?)
>>>>>>
>>>>>
>>>>> More or less: it was not an oversight.
>>>>> The summaries are not really part of the IR, it is more like an
>>>>> "analysis result" that is serialized. It can always be recomputed from the
>>>>> IR. This aspect makes it quite "special", it is the only analysis result
>>>>> that I know of that we serialize.
>>>>>
>>>>
>>>> The use list work seems pretty similar in some ways (granted, can't be
>>>> recomputed to match, hence the desire to serialize it for test case
>>>> implementation).
>>>>
>>>
>>> I see use-list as a leaky implementation detail of the IR that we
>>> serialized because it impact the processing of the IR.
>>>
>>> Summaries are more like serializing the CFG for example.
>>>
>>>
>>>> But it looks like the same is true here to a degree - there are test
>>>> cases that exercise the summary handling, so they want summaries for input
>>>> (for now, I think, I've seen test cases that run another LLVM tool to
>>>> insert/create a summary to then feed that back in for a test), or to test
>>>> that the resulting summary is correct.
>>>>
>>>
>>> We have cases were we want summaries as an input and check a combined
>>> summary as an output, and for these having the YAML representation will be
>>> useful (we didn't have it before).
>>>
>>>
>>>>
>>>> Can summaries be standalone? I thought they could (that'd be ideal for
>>>> the distributed situation - only the summary needs to go to the 'thin link'
>>>> step, I think? (currently maybe only the debug info is stripped for that -
>>>> but ideally other unused IR wouldn't be shipped there as well, I would
>>>> think)
>>>>
>>>
>>> Yes conceptually they can be standalone.
>>>
>>>
>>>>
>>>>
>>>>>
>>>>>
>>>>>> & now there's an effort to correct that.
>>>>>>
>>>>>
>>>>> The main motivation here, I believe, is more to help dev to have human
>>>>> readable/understandable dump for ThinLTO bitcodes. Having to inspect
>>>>> separately summaries is a pain.
>>>>>
>>>>
>>>> Not sure I quite follow - inspect separately?
>>>>
>>>
>>> llvm-dis does not display summaries today, so you can't just use
>>> llvm-dis like a "regular" flow.
>>>
>>>
>>>> How are they inspected today?
>>>>
>>>
>>> llvm-bcanalyzer? And now the YAML dump as well.
>>>
>>>
>>>> & also, I think there are test cases that want to/are currently testing
>>>> summary input but do so somewhat awkwardly by using another tool to produce
>>>> the summary first. Ideally the test case would have the summary written in
>>>> to start, I would think, if that's a codepath worth testing?
>>>>
>>>
>>> The IR already contains all the information, so why repeating it? This
>>> makes the test case harder to maintain, in the vast majority, I expect that
>>> if a test needs IR then it shouldn't need to include a summary as well (and
>>> vice-versa).
>>>
>>> In the majority of test we have we want to check if the importing does
>>> what it is supposed to do, and if the linkage are correctly adjusted. With
>>> a YAML (or other) serialization for the summaries this could indeed been
>>> done purely with summaries, without any IR involved.
>>>
>>> --
>>> Mehdi
>>>
>>>
>>>
>>>
>>>
>>>
>>>>
>>>> - Dave
>>>>
>>>>
>>>>>
>>>>> --
>>>>> Mehdi
>>>>>
>>>>> So it seems like that would start with a discussion of what the right
>>>>>> end-state would be: What the syntax in textual IR should be, then
>>>>>> implementing it. I can understand implementing such a thing in steps - it's
>>>>>> perhaps more involved than the COMDAT situation. In that case starting on
>>>>>> either side seems fine - implementing the emission first (hidden behind a
>>>>>> flag, so as not to break round-tripping in the interim) or the parsing
>>>>>> first (no need to hide it behind any flags - manually written examples can
>>>>>> be used as input tests).
>>>>>>
>>>>>> (& it sounds like there's some partially implemented functionality
>>>>>> using a YAML format that was intended to address how some test cases could
>>>>>> be written? & this might be a good basis for the syntax - but seems to me
>>>>>> like it might be a bit disjointed/out of place in the textual IR format
>>>>>> that's not otherwise YAML-based?)
>>>>>>
>>>>>> - Dave
>>>>>>
>>>>>> On Fri, Jun 2, 2017 at 8:46 AM Charles Saternos via llvm-dev <
>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>>> Hey all,
>>>>>>>
>>>>>>> Below is the proposed format for the dump of the ThinLTO module
>>>>>>> summary in the llvm-dis utility:
>>>>>>>
>>>>>>> > ../build/bin/llvm-dis t.o && cat t.o.ll
>>>>>>> ; ModuleID = '2.o'
>>>>>>> source_filename = "2.ll"
>>>>>>> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>>>>>>> target triple = "x86_64-unknown-linux-gnu"
>>>>>>>
>>>>>>> @X = constant i32 42, section "foo", align 4
>>>>>>>
>>>>>>> @a = weak alias i32, i32* @X
>>>>>>>
>>>>>>> define void @afun() {
>>>>>>> %1 = load i32, i32* @a
>>>>>>> ret void
>>>>>>> }
>>>>>>>
>>>>>>> define void @testtest() {
>>>>>>> tail call void @boop()
>>>>>>> ret void
>>>>>>> }
>>>>>>>
>>>>>>> declare void @boop()
>>>>>>>
>>>>>>> ; Module summary:
>>>>>>> ; testtest (External linkage)
>>>>>>> ; Function (2 instructions)
>>>>>>> ; Calls: boop
>>>>>>> ; X (External linkage)
>>>>>>> ; Global Variable
>>>>>>> ; afun (External linkage)
>>>>>>> ; Function (2 instructions)
>>>>>>> ; Refs:
>>>>>>> ; a
>>>>>>> ; a (Weak any linkage)
>>>>>>> ; Alias (aliasee X)
>>>>>>>
>>>>>>> I've implemented the above format in the llvm-dis utility, since
>>>>>>> there currently isn't really a way of getting ThinLTO summaries in a
>>>>>>> human-readable format.
>>>>>>>
>>>>>>> Let me know what you think of this format, and what information you
>>>>>>> think should be added/removed.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Charles
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> LLVM Developers mailing list
>>>>>>> llvm-dev at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>>
>>>
>>
>
>
> --
> Teresa Johnson | Software Engineer | tejohnson at google.com |
> 408-460-2413 <(408)%20460-2413>
>
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