[RS6000] "G" and "H" constraints

[RS6000] "G" and "H" constraints

The patch fixes two cases where the "G" and "H" constraints were used
incorrectly.  Their purpose is calculating insn lengths.  Thus it
never makes sense to put "GH" together or with "F" in an insn
alternative.

movdi_internal32 used "GHF" in an alternative so I replaced that with
"F", and added length attributes for the insn, which were missing.
There are some formatting changes too, to make alternatives line up
with attributes.

The FMOVE128 version of mov<mode>_softfloat also had "GHF" in an
alternative, so "GH" is dropped and "F" moved to a separate
alternative in order to get insn lengths correct.  Well by correct I
mean we need to choose the maximum insn length otherwise branches
might not reach.  Note the very large length for "F".  I think it
would be better to force soft-float long double constants to memory in
64-bit mode, but that's a patch for another day.

	* config/rs6000/constraints.md (G, H): Comment on purpose of
	constraint.  Correct mode comments and "G" mode test.
	* config/rs6000/rs6000.md (movdi_internal32): Remove "GH" from
	alternative handling "F".  Add length attr.  Formatting.
	(mov<mode>_softfloat <FMOVE128>): Delete "GH" from
	alternative, and move "F" to separate alternative.  Correct
	insn lengths.

From-SVN: r266607