[LLVMdev] Disabling x87 instructions for a sub-target

[Benjamin Kramer]

On 04.04.2012, at 21:45, Murali, Sriram wrote:

> Hello there,
> I recently started working on the LLVM backend for a target that doesn’t support x87 instructions.
> Currently, I am in the process of completely disabling some x87 instructions such as fcomi, fcompi,… for a specific sub-target. I also do not have SSE enabled for my sub-target, and llvm resorts to fcomi* instructions for FP compare instructions.
>  
> Is there a way to bypass the automatic optimization that generates the x87 instructions when SSE is disabled, and completely eliminate the code generation for the same(error out)?

A simple trick without requiring code changes is forcing the code generator to use soft fp (llc -soft-float). It will generate libcalls instead of x87 instructions for any floating point operations. The compile will then fail at link time because libcompiler-rt/libgcc don't supply those function for x86.

- Ben

> Thanks
>  
> Sriram Murali
> +1 (519) 772-2579
>  
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