[llvm-dev] Question about llvm::Value::print performance

[Dr.-Ing. Christoph Cullmann via llvm-dev]

Hi,

> Hi Christoph,
> 
> is it possible to reduce the amount of "work" for every process and
> iterate over all functions in different processes?
> I mean: Debug the first 100 functions, then in the socond step, debug
> function 101 till 200, and so on. So you summarize and complete your
> result over several, standalone debugs steps.
not really, I need the graph with instruction labels in one go, as it will be used to visualize things,
e.g. like this example that works on PPC assembly. (a bit like writing a dot graph of the IR)

https://www.absint.com/stackanalyzer/shot5.png

Beside, as the printing seems really like "per instruction redo all type importing and co."
it won't even scale if I let all cores do things.

The AssemblyWriter that is internal has rather clever caching for that which I can't access
from the outside, if I am not wrong.

But perhaps somebody has a clever way around this issue.

Greetings
Christoph

> 
> Best regards,
> Thomas
> 
> Am 05.06.2017 16:43 schrieb Dr.-Ing. Christoph Cullmann via llvm-dev:
>> Dear Thomas,
>> 
>>> Hi Christoph,
>>> 
>>> maybe there is a way of caching the print outputs and output them at
>>> the
>>> end of the program execution?
>>> So, your real application do not have this kind of bottle neck.
>> this is a valid idea, thought the problem is: I output all things only
>> "once" and I even
>> output it like:
>> 
>> 1) load module
>> 2) go over functions
>> 3) output all blocks with instructions in the current function
>> 
>> That allows to e.g. use ModuleSlotTracker to compute the <label>
>> comments of blocks fast,
>> as each function is only visited once.
>> 
>> Still, the performance drop to just print each instruction once is
>> "large", without instruction printing
>> my control flow graph construction works in ~1 second, with printing I
>> aborted after some minutes the execution.
>> 
>> (the module is really large, linked full graph of some medium sized
>> application, around 5000 functions and 500k instructions
>> and a lot of debug/type info)
>> 
>> If there is some way that I precompute things on my own, I would
>> really like to use that, but I don't see a way
>> to do that.
>> 
>> Greetings
>> Christoph
>> 
>>> 
>>> Best regards,
>>> Thomas
>>> 
>>> Am 05.06.2017 16:30 schrieb Dr.-Ing. Christoph Cullmann via llvm-dev:
>>>> Hi,
>>>> 
>>>> I want to use llvm::Value::print to output the assembly strings for
>>>> llvm::Instructions
>>>> inside a rather large llvm::Module (linked module with lots of
>>>> types/...).
>>>> 
>>>> I started with plain ::print and switched over to
>>>> 
>>>> http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html#a04e6fc765eeb0c4c90ac5d55113db116
>>>> 
>>>> with a ModuleSlotTracker I pass in myself to avoid some complexity.
>>>> 
>>>> Still now I have the issue that the TypeFinder::run and related that
>>>> is done internally
>>>> by each print still is 99% of my program runtime. (at least perf
>>>> tells
>>>> me that)
>>>> 
>>>> Is there any clever workaround for this?
>>>> 
>>>> I looked a bit through the sources but it seems that no API is
>>>> exported that would allow a faster print
>>>> call.
>>>> 
>>>> Given I want the output only more or less as "debugging" annotation
>>>> to
>>>> my graph, is there some other
>>>> "fast" way to print instructions, even if some info is missing then?
>>>> 
>>>> Greetings
>>>> Christoph
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