workaround for "error: more than 30 operands in 'asm'"?

[Ian Lance Taylor]

"Clem Taylor" <clem.taylor@gmail.com> writes:

> I'm working on taking PowerPC VMX code that uses altivec intrinsics
> and rescheduling it with inline assembly. gcc is making some fairly
> bad scheduling choices in with the code, resulting in code that is
> running 4x slower then I was hoping for. I have a simplified version
> working, but with the real version gcc is failing with: "error: more
> than 30 operands in 'asm'". The code is using 28 vector registers and
> 6 serial registers.
>
> The code is a mixture of setup code in C and only the inner loop is in
> assembly, so it wouldn't be convenient to write this directly in
> assembly. Also, because the code is highly pipelined (to overcome the
> latency of the VMX floating point unit) it is a mess to split this up
> into multiple asm() statements. Beyond recompiling gcc with a larger
> operand count, is there a workaround for this problem?

Use fewer operands?  Otherwise, no.  It's a hard limit in gcc.

Since you mention the number of registers you are using, note that
that only matters if they are inputs or outputs.  If you need a
temporary register, just pick one, and add it the clobber list.  But
if you really have that many inputs and outputs, then you are stuck.

Ian