[PATCH], PR target/81593, Optimize PowerPC vector sets coming from a vector extracts

[Michael Meissner <meissner at linux dot vnet dot ibm dot com>]

This patches optimizes the PowerPC vector set operation for 64-bit doubles and
longs where the elements in the vector set may have been extracted from another
vector (PR target/81593):

Here an an example:

	vector double
	test_vpasted (vector double high, vector double low)
	{
	  vector double res;
	  res[1] = high[1];
	  res[0] = low[0];
	  return res;
	}

Previously it would generate:

        xxpermdi 12,34,34,2
        vspltisw 2,0
        xxlor 0,35,35
        xxpermdi 34,34,12,0
        xxpermdi 34,0,34,1

and with these patches, it now generates:

        xxpermdi 34,35,34,1

I have tested it on a little endian power8 system and a big endian power7
system with the usual bootstrap and make checks with no regressions.  Can I
check this into the trunk?

I also built Spec 2006 with the compiler, and saw no changes in the code
generated.  This isn't surprising because it isn't something that auto
vectorization might generate by default.

[gcc]
2017-07-27  Michael Meissner  <meissner@linux.vnet.ibm.com>

	PR target/81593
	* config/rs6000/rs6000-protos.h (rs6000_emit_xxpermdi): New
	declaration.
	* config/rs6000/rs6000.c (rs6000_emit_xxpermdi): New function to
	emit XXPERMDI accessing either double word in either vector
	register inputs.
	* config/rs6000/vsx.md (vsx_concat_<mode>, VSX_D iterator):
	Rewrite VEC_CONCAT insn to call rs6000_emit_xxpermdi.  Simplify
	the constraints with the removal of the -mupper-regs-* switches.
	(vsx_concat_<mode>_1): New combiner insns to optimize CONCATs
	where either register might have come from VEC_SELECT.
	(vsx_concat_<mode>_2): Likewise.
	(vsx_concat_<mode>_3): Likewise.
	(vsx_set_<mode>, VSX_D iterator): Rewrite insn to generate a
	VEC_CONCAT rather than use an UNSPEC to specify the option.

[gcc/testsuite]
2017-07-27  Michael Meissner  <meissner@linux.vnet.ibm.com>

	PR target/81593
	* gcc.target/powerpc/vsx-extract-6.c: New test.
	* gcc.target/powerpc/vsx-extract-7.c: Likewise.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797

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