llvm dev - Jul 2008 - [LLVMdev] runtime optimizations in LLVM

Hello,

 (im new to LLVM , so pl excuse if this is a naive q).

  Can someone provide info on what runtime
optimizations are done in LLVM? do you have something
along lines of JVM's hotspot feature?

 How efficient is the optimized code vis-a-vis native
code?

thanks
-kamal
 




     
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Hi Kamal,

On Jan 2, 2008, at 05:57, Kamal R. Prasad wrote:
> (im new to LLVM , so pl excuse if this is a naive q).
Welcome!
> Can someone provide info on what runtime optimizations are done in  
> LLVM?
You can use any of LLVM's optimizing transformations in a JIT context.  
There's a list here:

http://llvm.org/docs/Passes.html

Unlike Java, you're in the driver's seat. You can determine which  
optimizations are applied to your code, and when.
> do you have something along lines of JVM's hotspot feature?
You can recompile a function in the JIT at any time.

http://llvm.org/doxygen/classllvm_1_1ExecutionEngine.html#a18

However, LLVM does not yet have support frame rewriting; you cannot re- 
optimize and resume a function that is on the call stack.
> How efficient is the optimized code vis-a-vis native code?
It is native code! :) LLVM is also an excellent static compiler (see  
llvm-gcc, clang).

— Gordon

--- On Thu, 1/3/08, Gordon Henriksen <gordonhenriksen at mac.com>
wrote:
> 
> On Jan 2, 2008, at 05:57, Kamal R. Prasad wrote:
> 
> > (im new to LLVM , so pl excuse if this is a naive q).
> 
> Welcome!
> 
thanks
> > Can someone provide info on what runtime optimizations
> are done in  
> > LLVM?
> 
> You can use any of LLVM's optimizing transformations in
> a JIT context.  
> There's a list here:
> 
> http://llvm.org/docs/Passes.html
> 
> Unlike Java, you're in the driver's seat. You can
> determine which  
> optimizations are applied to your code, and when.
> 
yes -but can you tell me which optimizations have been proven to be more
effective when applied at run time i.e. when input data is available?
> > do you have something along lines of JVM's hotspot
> feature?
> 
> You can recompile a function in the JIT at any time.
> 
I am interested in optimizing code that was compiled using a C/C++ compiler. So,
I will have binaries but probably not the source code.
> http://llvm.org/doxygen/classllvm_1_1ExecutionEngine.html#a18
> 
> However, LLVM does not yet have support frame rewriting;
> you cannot re- 
> optimize and resume a function that is on the call stack.
> 
> > How efficient is the optimized code vis-a-vis native
> code?
> 
> It is native code! :) LLVM is also an excellent static
> compiler (see  
> llvm-gcc, clang).
> 
can I pull out the backend part which is used for runtime optimization?

thanks
kamal
> — Gordon