[LLVMdev] Request for Help: Teach ARM target to auto-detect cpu / subtarget features

[James Molloy]

On 11/05/12 04:56, 陳韋任 wrote:
>> I've just filed PR12794: Add ARM cpu / subtarget features auto-detection. And I would very much appreciate the community's help to implement this.
>>
>> What motivated this? Well this:
>> http://www.phoronix.com/scan.php?page=news_item&px=MTA5OTM
>>
>> I believe one of the reason the benchmark numbers are totally bogus is that the compilation are done on ARM hosts. Given the benchmarks are apparently compiled without -mcpu=cortex-a9, I suspect LLVM ended up generating code for "generic" ARMv4 cpu. This article makes me sick in my stomach.
>    I skip through MCTargetDesc/ARMAsmBackend.cpp, it seems llvm::createARMAsmBackend
> only pickup different ARM ISA for Darwin. As for Linux, I guess we need to tweak
> ELFARMAsmBackend? Do we need to modify Clang as well?
>
> Regards,
> chenwj
>
The backend sounds like the wrong place to implement this feature.

I'd have thought the Clang driver would be the ideal place?