[PATCH], PR target/67071, Improve easy_altivec_constants on PowerPC

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

In preparing the next IEEE 128-bit floating point patch, I needed a quick way
to load -0.0q into a vector registers (i.e. just the MSB set). I originally had
a special purpose insn to load this value, but I decided to widen it to allow
the easy_altivec_constant support to generate constants where you use the
VSLDOI instruction to create the bottom part of all 0's or all 1's.

When I started doing the coding, I noticed that the current support to load
vectors with the MSB set in each element no longer worked, because the test
assumed the constant was stored as an unsigned value, and we now store a sign
extended number. I raised PR 67071 about this, and this patch fixes that
problem and adds more patterns of vector constants that can be loaded without
using memory.

I have built this on both big endian power7 and little endian power8 machines
with no regressions. Can I install the patch? I would also like to backport
this patch to the active branches.

[gcc]
2015-08-03  Michael Meissner  <meissner@linux.vnet.ibm.com>

	PR target/67071
	* config/rs6000/predicates.md (easy_vector_constant_vsldoi): New
	predicate to allow construction of vector constants using the
	VSLDOI vector shift instruction.

	* config/rs6000/rs6000-protos.h (vspltis_shifted): Add
	declaration.

	* config/rs6000/rs6000.c (vspltis_shifted): New function to return
	the number of bytes to be shifted left and filled in with either
	all zero or all one bits.
	(gen_easy_altivec_constant): Call vsplitis_shifted if no other
	methods exist.
	(output_vec_const_move): On power8, generate XXLORC to generate
	a vector constant with all 1's. Do a split if we need to use a
	VSLDOI instruction.

	* config/rs6000/rs6000.h (EASY_VECTOR_MSB): Use mode mask to
	properly test for the MSB.

	* config/rs6000/altivec.md (VSLDOI splitter): Add splitter for
	vector constants that can be created with VSLDOI.

[gcc/testsuite]
2015-08-03  Michael Meissner  <meissner@linux.vnet.ibm.com>

	PR target/67071
	* gcc.target/powerpc/pr67071-1.c: New file to test PR 67071 new
	vector constants.
	* gcc.target/powerpc/pr67071-2.c: Likewise.
	* gcc.target/powerpc/pr67071-3.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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