[5/10] Add vect_perm3_* target selectors

[Jeff Law]

On 11/03/2017 10:19 AM, Richard Sandiford wrote:
> SLP load permutation fails if any individual permutation requires more
> than two vector inputs.  For 128-bit vectors, it's possible to permute
> 3 contiguous loads of 32-bit and 8-bit elements, but not 16-bit elements
> or 64-bit elements.  The results are reversed for 256-bit vectors,
> and so on for wider vectors.
> 
> This patch adds a routine that tests whether a permute will require
> three vectors for a given vector count and element size, then adds
> vect_perm3_* target selectors for the cases that we currently use.
> 
> 
> 2017-11-03  Richard Sandiford  <richard.sandiford@linaro.org>
> 	    Alan Hayward  <alan.hayward@arm.com>
> 	    David Sherwood  <david.sherwood@arm.com>
> 
> gcc/
> 	* doc/sourcebuild.texi (vect_perm_short, vect_perm_byte): Document
> 	previously undocumented selectors.
> 	(vect_perm3_byte, vect_perm3_short, vect_perm3_int): Document.
> 
> gcc/testsuite/
> 	* lib/target-supports.exp (vect_perm_supported): New proc.
> 	(check_effective_target_vect_perm3_int): Likewise.
> 	(check_effective_target_vect_perm3_short): Likewise.
> 	(check_effective_target_vect_perm3_byte): Likewise.
> 	* gcc.dg/vect/slp-perm-1.c: Expect SLP load permutation to
> 	succeed if vect_perm3_int.
> 	* gcc.dg/vect/slp-perm-5.c: Likewise.
> 	* gcc.dg/vect/slp-perm-6.c: Likewise.
> 	* gcc.dg/vect/slp-perm-7.c: Likewise.
> 	* gcc.dg/vect/slp-perm-8.c: Likewise vect_perm3_byte.
> 	* gcc.dg/vect/slp-perm-9.c: Likewise vect_perm3_short.
> 	Use vect_perm_short instead of vect_perm.  Add a scan-tree-dump-not
> 	test for vect_perm3_short targets.
Going to take your word on the correctness of vect_perm_supported. :-)

OK for the trunk.

jeff