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Re: [PATCH][RS6000] Fix PR87870: ppc64 generates poor code when loading constants into TImode vars


On 12/14/18 8:23 PM, Segher Boessenkool wrote:
> On Thu, Dec 13, 2018 at 10:59:36AM -0600, Peter Bergner wrote:
>> For the alternatives
>> I'm changing, we're loading into GPR regs and these alternatives are always
>> split (split2), so these length values are never used/seen at final assembly
>> time.
> 
> But some move instructions are created *after* split2.

That may be so, but I do not know how we could create a move insn using
this alternative, since rs6000_output_move_128bit() does the following
for this alternative (ie, loading a constant into a GPR):


  /* Constants.  */
  else if (dest_regno >= 0
           && (GET_CODE (src) == CONST_INT
               || GET_CODE (src) == CONST_WIDE_INT
               || GET_CODE (src) == CONST_DOUBLE
               || GET_CODE (src) == CONST_VECTOR))
    {
      if (dest_gpr_p)
        return "#";

This means we require the insn to eventually be split and not reach final
assembly, does it not?

Peter


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