Re: RFA: Fix modes in ctz libcall notes

[Paolo Bonzini <bonzini at gnu dot org>]

Richard Sandiford wrote:
> Paolo Bonzini <bonzini@gnu.org> writes:
> > > -      emit_libcall_block (insns, target, value,
> > > -			  gen_rtx_fmt_e (unoptab->code, outmode, op0));
> > > +      eq_value = gen_rtx_fmt_e (unoptab->code, mode, op0);
> > > +      if (GET_MODE_SIZE (outmode) < GET_MODE_SIZE (mode))
> > > +	eq_value = gen_rtx_TRUNCATE (outmode, eq_value);
> > Why not simplifying this so that a SUBREG is created instead?
>
> Having SUBREGs of anything other than MEMs and REGs seems less
> than ideal.  (For reference, we use TRUNCATEs for a similar
> purpose when doing high-part multiplications.)

My thought was that fwprop or CSE will probably create it anyway 
(because they simplify) and I just wondered whether having a more 
canonical representation would be better.  However, you're right that 
the more canonical representation may be less ideal.

Paolo