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Re: RFA: Fix modes in ctz libcall notes


Paolo Bonzini <bonzini@gnu.org> writes:
> 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.

So you'd like to see rtl_hooks.gen_lowpart_no_emit instead?

Richard


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