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

Dr.-Ing. Christoph Cullmann via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 5 07:55:18 PDT 2017


> 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)


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.


> 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
>>> _______________________________________________
>>> 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

----------------------------- Dr.-Ing. Christoph Cullmann ---------
AbsInt Angewandte Informatik GmbH      Email: cullmann at AbsInt.com
Science Park 1                         Tel:   +49-681-38360-22
66123 Saarbrücken                      Fax:   +49-681-38360-20
GERMANY                                WWW:   http://www.AbsInt.com
Geschäftsführung: Dr.-Ing. Christian Ferdinand
Eingetragen im Handelsregister des Amtsgerichts Saarbrücken, HRB 11234

More information about the llvm-dev mailing list