…s.Compare with asm on ppc64x

bytes: fix typo in ppc64le asm for Compare

Correcting a line in asm_ppc64x.s in the cmpbodyLE function
that originally was R14 but accidentally changed to R4.

Fixes golang#17488

Change-Id: Id4ca6fb2e0cd81251557a0627e17b5e734c39e01
Reviewed-on: https://go-review.googlesource.com/31266
Reviewed-by: Michael Munday <munday@ca.ibm.com>
Run-TryBot: Michael Munday <munday@ca.ibm.com>

Backport of 2190f77
by Lynn Boger <laboger@linux.vnet.ibm.com>

bytes: improve performance for bytes.Compare on ppc64x

This improves the performance for byte.Compare by rewriting
the cmpbody function in runtime/asm_ppc64x.s.  The previous code
had a simple loop which loaded a pair of bytes and compared them,
which is inefficient for long buffers.  The updated function checks
for 8 or 32 byte chunks and then loads and compares double words where
possible.

Because the byte.Compare result indicates greater or less than,
the doubleword loads must take endianness into account, using a
byte reversed load in the little endian case.

Fixes golang#17433

benchmark                                   old ns/op     new ns/op     delta
BenchmarkBytesCompare/8-16                  13.6          7.16          -47.35%
BenchmarkBytesCompare/16-16                 25.7          7.83          -69.53%
BenchmarkBytesCompare/32-16                 38.1          7.78          -79.58%
BenchmarkBytesCompare/64-16                 63.0          10.6          -83.17%
BenchmarkBytesCompare/128-16                112           13.0          -88.39%
BenchmarkBytesCompare/256-16                211           28.1          -86.68%
BenchmarkBytesCompare/512-16                410           38.6          -90.59%
BenchmarkBytesCompare/1024-16               807           60.2          -92.54%
BenchmarkBytesCompare/2048-16               1601          103           -93.57%

Change-Id: I121acc74fcd27c430797647b8d682eb0607c63eb
Reviewed-on: https://go-review.googlesource.com/30949
Reviewed-by: David Chase <drchase@google.com>

Backport of 1e28dce
by Lynn Boger <laboger@linux.vnet.ibm.com>

math, cmd/internal/obj/ppc64: improve floor, ceil, trunc with asm

This adds the instructions frim, frip, and friz to the ppc64x
assembler for use in implementing the math.Floor, math.Ceil, and
math.Trunc functions to improve performance.

Fixes golang#17185

BenchmarkCeil-128                    21.4          6.99          -67.34%
BenchmarkFloor-128                   13.9          6.37          -54.17%
BenchmarkTrunc-128                   12.7          6.33          -50.16%

Change-Id: I96131bd4e8c9c8dbafb25bfeb544cf9d2dbb4282
Reviewed-on: https://go-review.googlesource.com/29654
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Michael Munday <munday@ca.ibm.com>

Backport of 3311275
by Lynn Boger <laboger@linux.vnet.ibm.com>