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

Dr.-Ing. Christoph Cullmann via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 5 07:43:14 PDT 2017

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.


> 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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