llvm dev - Mar 2011 - [LLVMdev] Profiling support in LLVM

Hello LLVM developers,

I'm assisting my doctor who is doing a research and he wants to use the llvm
compiler, my job is to profile build the benchmarks using llvm-prof.

What i want to know is the following

1- does llvm support profile feedback optimizations!?

2- when i've used the llvm-prof it's input is an object file (not binary
as other compilers) my question is how could I profile a whole benchmark program
using the llvm-prof ?

3- is there a way to print the spill code information (e.g. spill code count in
a single function or basic block) ?

your help is appreciated.

regards,
~Najem
 		 	   		  
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Hi Najem,

On Mar 21, 2011, at 9:47 AM, NaJeM ErMeLeH wrote:
> I'm assisting my doctor who is doing a research and he wants to use the
llvm compiler, my job is to profile build the benchmarks using llvm-prof.
> 
> What i want to know is the following
> 
> 1- does llvm support profile feedback optimizations!?
Not yet. Please see Bob's proposal:
http://article.gmane.org/gmane.comp.compilers.llvm.devel/37107/match=profile
> 2- when i've used the llvm-prof it's input is an object file (not
binary as other compilers) my question is how could I profile a whole benchmark
program using the llvm-prof ?
I haven't done it, but I think the correct answer is to use llvm-ld to
generate a single bitcode file, then run llvm-prof.
> 3- is there a way to print the spill code information (e.g. spill code
count in a single function or basic block) ?
-stats give you aggregate counts. Unfortunately, I don't know a way to do
per-function reporting without using llvm-extract.

You might be able to scrape -debug-only=spiller output for block info.

-Andy
> your help is appreciated.
> 
> regards,
> ~Najem
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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Dear Najem,

You might want to read the llvm-prof documentation if you haven't 
already: http://llvm.org/cmds/llvm-prof.html.  The documentation 
mentions a script in the utils directory that automates some of the 
profiling tasks for you.

I suspect the way that llvm-prof works is to compile your whole program 
to a single LLVM bitcode file, run a transform on it, and then generate 
native code, link in the LLVM profiling run-time library, and then run 
the program.  You then use llvm-prof to analyze the original bitcode 
file and the output from running the program to get the report.  That's 
just a guess, though; I've never used llvm-prof myself.

I bet looking at the script in the utils directory will shed light on 
how to use llvm-prof.

-- John T.


On 3/21/11 4:46 PM, Andrew Trick wrote:
> Hi Najem,
>
> On Mar 21, 2011, at 9:47 AM, NaJeM ErMeLeH wrote:
>> I'm assisting my doctor who is doing a research and he wants to use
>> the llvm compiler, my job is to profile build the benchmarks using 
>> llvm-prof.
>>
>> What i want to know is the following
>>
>> 1- does llvm support profile feedback optimizations!?
>
> Not yet. Please see Bob's proposal:
>
http://article.gmane.org/gmane.comp.compilers.llvm.devel/37107/match=profile
>
>> 2- when i've used the llvm-prof it's input is an object file
(not
>> binary as other compilers) my question is how could I profile a whole 
>> benchmark program using the llvm-prof ?
>
> I haven't done it, but I think the correct answer is to use llvm-ld to 
> generate a single bitcode file, then run llvm-prof.
>
>> 3- is there a way to print the spill code information (e.g. spill 
>> code count in a single function or basic block) ?
>
> -stats give you aggregate counts. Unfortunately, I don't know a way to 
> do per-function reporting without using llvm-extract.
>
> You might be able to scrape -debug-only=spiller output for block info.
>
> -Andy
>
>> your help is appreciated.
>>
>> regards,
>> ~Najem
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu <mailto:LLVMdev at
cs.uiuc.edu>http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
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