llvm dev - Jul 2011 - [LLVMdev] [cfe-dev] should -mno-sse -mno-mmx -msse -mmmx work?

Hi Andrew-
> fatal error: error in backend: SSE2 register return with SSE2 disabled
Is this for 32-bit or 64-bit x86? If it's the latter, the ABI demands
that the return value in this case is in xmm0 - SSE is required.

Alistair

On Jul 1, 2011, at 2:43 PM, Alistair Lynn wrote:
> Hi Andrew-
> 
>> fatal error: error in backend: SSE2 register return with SSE2 disabled
> 
> Is this for 32-bit or 64-bit x86?
64-bit x86.
> If it's the latter, the ABI demands
> that the return value in this case is in xmm0 - SSE is required.
> 
Well -no-sse -mno-mmx works for EFI as it is pre-boot firmware and does not have
any floating point C code.  We use -no-sse and -mno-mmx code to prevent
optimized code gen using these registers for optimizations.

Andrew

Hi Andrew-
> Well -no-sse -mno-mmx works for EFI as it is pre-boot firmware and does not
have any floating point C code.  We use -no-sse and -mno-mmx code to prevent
optimized code gen using these registers for optimizations.
Whether it's optimised or not doesn't particularly matter, the x86_64
ABI says that floating-point return values go into SSE registers, so that is
where LLVM is required to put them. If you need to avoid these registers, then
you may well need to write a separate calling convention for the backend which
stores those return values elsewhere (like the x87 fp stack), or just do not
return floating-point values.

Alistair