[LLVMdev] Gold plugin: emit LLVM after LTO?

[Shuxin Yang]

The Apple ld (shipped with Xcode, open-source) saves the 3 files if 
-save-temps is applied:
   - xxx.lto.bc : the merged bit-code before IPA
   - xxx.lto.opt.bc: the optimized bit-code of the *.lto.bc
   - xxx.lto.o : the object file of xxx.lto.bc

I think it is better way to go, often time we need IR both after and 
after the transformation.

On 6/4/13 3:37 AM, Jonas Wagner wrote:
>
>     > I often use the gold plugin's also-emit-llvm option to verify the final LLVM
>
>         bitcode of a program. However, I realized that the gold plugin
>         generates the
>         bitcode file before running LTO optimizations, such that the
>         changes performed
>         by LTO are not reflected in the bitcode file.
>
>         What is the reason for this behavior?
>
>
>     my guess: if the LTO optimizers crash, this is very helpful for
>     debugging
>     because it gives you the input to the optimizers.
>
>
> This is true. It also means that if the LTO optimizers don't crash, 
> the bitcode is out of sync with the program. And not crashing is more 
> common than crashing ;)
>
> The question is whether also-emit-llvm is an option intended for LTO 
> debuggers or for LLVM end-users. I'd argue that it is very useful for 
> end-users, and that LTO developers could get the bitcode through other 
> means if they are researching a crash. At least from my personal point 
> of view, I use also-emit-llvm frequently despite not working on LTO. 
> How do other people use this?
>
> Best,
> Jonas
>
>
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