Re: PATCH: Use PLUS instead of HIGH/LO_SUM for large constants

[law at redhat dot com]

  In message <200109221911.f8MJBCM1023599@hiauly1.hia.nrc.ca>you write:
  > Because the semantics of HIGH/LO_SUM are not well determined, it is prefera
  > ble
  > to use PLUS to load large constants which need to be split into high and lo
  > w
  > parts.  This allows the constant's value to be recocognized during jump
  > expansion and thereby improves deadcode elimination.  As a result, other
  > optimisers shouldn't have to work as hard.  There is the further advantage
  > that the "high" part may be common for several constants and pulled out
  > of loops, etc.
  > 
  > This patch adds the capability to use PLUS on the PA if the constant
  > can be loaded into a register with a ldil/ldo instruction sequence.
  > This is the most common situation.  Really large values are still handled
  > with the old code.
  > 
  > Bootstrap checked with no regressions on hppa1.1-hp-hpux10.20.
  > 
  > OK?
  > 
  > Dave
  > -- 
  > J. David Anglin                                  dave.anglin@nrc.ca
  > National Research Council of Canada              (613) 990-0752 (FAX: 952-6
  > 605)
  > 
  > 2001-09-15  John David Anglin  <dave@hiauly1.hia.nrc.ca>
  > 
  > 	* pa.c (cint_split_ok): New function.
  > 	(emit_move_sequence): When loading a constant into a register, use
  > 	PLUS instead of HIGH/LO_SUM if the constant can be split and loaded
  > 	with a ldil/ldo instruction sequence.
  > 	* pa.md: New addmove pattern for adding constant_int to HImode
  > 	register and moving result to HImode register.
OK.  I've looked at this in a little more detail.

The one thing that still doesn't make any sense to me is the need for a
HImode addition pattern.  Can you figure out why this is needed and explain
it to me.

The rest of the patch seems pretty reasonable, though I'd like to have
a resolution on why an addhi3 pattern was added before installing anything.

jeff