[LLVMdev] Tutorial on writing Link Time Optimization Passes?

[Nick Lewycky]

The documentation you're looking for is:

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

If you're doing an optimization that runs at link-time, you'll probably 
be writing a ModulePass. You can run any pass at any time over any 
bitcode file with 'opt -mypass file.bc'. If you want to add it to the 
list of passes that run when linking via libLTO or llvm-ld, you can add 
it to the list in tools/llvm-ld/Optimize.cpp:Optimize and 
tools/lto/LTOCodeGenerator.cpp:generateAssemblyCode.

A couple other pointers to our doxygen:

   ModulePass: http://llvm.org/doxygen/classllvm_1_1ModulePass.html
   CallGraph: http://llvm.org/doxygen/classllvm_1_1CallGraph.html

You can take a look at lib/Transforms/IPO/Internalize.cpp to see an 
example of a link-time optimization pass that uses the CallGraph.

Nick

Diego Huang wrote:
> Hi,
> 
> Is there a tutorial on how to get started with writing link-time  
> optimization passes? The documentation at  
> http://www.llvm.org/docs/LinkTimeOptimization.html explains the design  
> of the LTO interface, but does not explain where to start writing  
> code. Would my pass go inside libLTO.a or is it separate from  
> libLTO.a? What I would like to be able to do is traverse through the  
> entire call graph of the program, which is only available at link-time.
> 
> Thank you,
> 
> Diego
> 
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