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

[Ian Lance Taylor <iant@google.com>]

Andrew Haley <aph@redhat.com> writes:

> Ian Lance Taylor wrote:
>> "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.
>
> Isn't this trivially fixed by changing:
>
>   /* Allow at least 30 operands for the sake of asm constructs.  */
>   /* ??? We *really* ought to reorganize things such that there
>      is no fixed upper bound.  */
>   max_recog_operands = 29;  /* We will add 1 later.  */
>   max_dup_operands = 1;
>
> in genconfig.c ?

Yes.  Sorry for being confusing, I was answering the question "beyond
recompiling gcc...."

Ian