Re: CVS commit: src/sys/arch

[Matt Thomas <matt%3am-software.com@localhost>]

On Feb 5, 2014, at 3:43 PM, David Laight <david%l8s.co.uk@localhost> wrote:

> On Wed, Feb 05, 2014 at 03:09:59PM -0800, Matt Thomas wrote:
>> 
>>>> 
>>>> This breaks clang. Please do not depend on one SSE option disabling
>>>> another.
>>> 
>>> Without those flags I believe gcc might generate x87 instructions.
>>> Quite possibly even for amd64.
>>> See a very recent linux fix.
>>> Try searching for: Disable generation of traditional x87 instructions
>> 
>> I think Joerg is saying put in -mno-sse2 since that is not disabled
>> by -mno-sse when using clang.
> 
> with the gcc I'm looking at (if I'm reading to code properly):
> no-sse => no-sse2 => no-sse3 => no-ssse3 & no-sse4a => no-sse4_1
> => no-sse4_2 => no-avx => no-fma => no-fma4

But clang is not gcc. :)

> You either need all of them, and the one that the next sub-version
> of the cpu/compiler add, or you assume that the first ones imply the
> latter - at least to some degree.

From llvm/dist/llvm/lib/Target/X86/X86.td:

// All x86-64 hardware has SSE2, but we don't mark SSE2 as an implied
// feature, because SSE2 can be disabled (e.g. for compiling OS kernels)
// without disabling 64-bit mode.