[Pixman] clang 3.0: Unsupported asm: input constraint with a matching output constraint of incompatible type!

Søren Sandmann sandmann at cs.au.dk
Wed May 30 20:05:30 PDT 2012

Ryan Schmidt <pixman-2012b at ryandesign.com> writes:

> On May 30, 2012, at 20:33, Søren Sandmann wrote:
>> Maybe the difference is that you are using "-O0" where Ryan is using
>> "-O2". The "K" constraint requires the argument to be compile-time
>> constant, which it is, but clang may not be able to see that without
>> optimization.
> Confirmed: If I set configure.optflags=-O0 on the command line, the
> configure check whether to use MMX intrinsics correctly says "no" and
> pixman builds. But with -O1 or the default -O2 it says "yes" and the
> build subsequently fails.
> Will using -O0 be detrimental to performance, or is that a viable
> workaround we could put into the MacPorts portfile?

Using -O0 will be catastrophic for performance. Pixman relies heavily on
compiler optimizations.

> Someone else in our ticket commented that we could use the
> --disable-mmx configure arg. Would that be better or worse?

Much better. Turning it off should have essentially no effect on
performance on typical x86 systems (it might actually be a tiny win),
including all x86 Macintoshes ever produced.


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