llvm dev - Jan 2008 - [LLVMdev] LTO ?

Hi folks,

I've got an idea for something I may be able to do as a Link-Time- 
Optimization pass,
but I can't seem to find how LTO gets used.  My crude approach has  
been to compile
LLVM for debugging, and then run gdb on llvm-ld with -O5 and two .bc  
files, trying to
catch LTO in action.   I've also scanned the compiled tools, and none  
of them appear
to use the symbol 'createLLVMOptimizer' (or anything with 'lto',
etc).  The document at
http://llvm.org/releases/2.1/docs/LinkTimeOptimization.html  doesn't  
seem to be of much
help for getting started with this.   How do I provoke LTO?  Any  
suggestions?

Thanks,

Jeff


Jeff Inman  -- jti at lanl.gov
Advanced Architectures for Computation
Los Alamos National Laboratory

You can use the opt tool to run passes explicitly.  For IPO passes to  
have much effect, you need to run -internalize first.

--Owen

On Jan 24, 2008, at 2:23 PM, Jeff Inman wrote:
> Hi folks,
>
> I've got an idea for something I may be able to do as a Link-Time-
> Optimization pass,
> but I can't seem to find how LTO gets used.  My crude approach has
> been to compile
> LLVM for debugging, and then run gdb on llvm-ld with -O5 and two .bc
> files, trying to
> catch LTO in action.   I've also scanned the compiled tools, and none
> of them appear
> to use the symbol 'createLLVMOptimizer' (or anything with
'lto',
> etc).  The document at
> http://llvm.org/releases/2.1/docs/LinkTimeOptimization.html  doesn't
> seem to be of much
> help for getting started with this.   How do I provoke LTO?  Any
> suggestions?
>
> Thanks,
>
> Jeff
>
>
> Jeff Inman  -- jti at lanl.gov
> Advanced Architectures for Computation
> Los Alamos National Laboratory
>
> _______________________________________________
> 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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On Jan 24, 2008, at 12:23 PM, Jeff Inman wrote:
> Hi folks,
>
> I've got an idea for something I may be able to do as a Link-Time-
> Optimization pass,
> but I can't seem to find how LTO gets used.  My crude approach has
> been to compile
> LLVM for debugging, and then run gdb on llvm-ld with -O5 and two .bc
> files, trying to
> catch LTO in action.
Then, you want to set up a break-point at tools/llvm-ld/Optimizer.cpp: 
109 Optimizer(Module *M)
>  I've also scanned the compiled tools, and none
> of them appear
> to use the symbol 'createLLVMOptimizer' (or anything with
'lto',
> etc).  The document at
> http://llvm.org/releases/2.1/docs/LinkTimeOptimization.html  doesn't
> seem to be of much
> help for getting started with this.
This document is intended for someone who wants to integrate LLVM  
optimizer in the system linker. If a system linker can optimizer LLVM  
bitcodes then that is one way to take advantage of LTO. Another  
approach is to use llvm-ld to join multiple .bc files together and  
optimize them using various interprocedural optimizations.
>   How do I provoke LTO?  Any
> suggestions?
>
> Thanks,
>
> Jeff
-
Devang