[patch] opt: Initialize asm printers to avoid DCE

[Tobias Grosser]

On 20/05/2014 22:54, Rafael Espíndola wrote:
> On 15 May 2014 03:51, Tobias Grosser <tobias at grosser.es> wrote:
>> Hi,
>>
>> I would like to ask for review for the following patch:
>>
>> To avoid dead code elimination of the assembly printers, this patch calls
>> InitializeAllAsmPrinters() from opt. This increases the static binary size
>> of 'opt' from 50MB -> 52MB on my system (all backends compiled) and causes
>> no measurable increase in the time needed to run 'make check'.
>>
>> Without initialising the assembly printers a shared library build of opt is
>> linked with these libraries whereas for a static build these libraries are
>> dead code eliminated. This is problematic for plugins
>> that use assembly printers, as they neither can rely on opt to provide this
>> functionality nor can they link the printers in themselves as this breaks
>> with a shared object build of opt.
>>
>> As the impact is rather minor and for platforms where even a tiny binary
>> size increase matters 'opt' is commonly not provided, I don't expect any
>> problems. Still, I would like to ask for other opinions.
>
> It seems odd to have asm printers in opt at all. I understand that is
> because of the current library organization, but I don't think it is
> an explicit design.

Right. This could probably be "fixed" but it seems the improvements in 
terms of code size are rather small.

> What is the plugin doing with the asm printer? Could it plugin in llc?

It is a LLVM-IR optimizer that extracts parts of the LLVM IR, translates 
them to PTX, stores the PTX in a global variable and generates calls to 
the CUDA run-time to load and run this code instead of the original code.

Do you think it would be better to immediately restructure opt's linking 
to not link the asm printers? I looked into this briefly, but it seems 
to be a larger refactoring that adds a lot of complexity.

Cheers,
Tobias