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

Thomas Kr├╝ger via llvm-dev llvm-dev at lists.llvm.org
Mon Jun 5 07:50:20 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.

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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