Clean up the IFUNC implementations for powerpc in order to remove
unneeded macro definitions.
Tested on ppc64le with and without --disable-multi-arch flag.
* sysdeps/powerpc/powerpc64/multiarch/stpcpy-power8.S: Define the
implementation-specific function name and remove unneeded macros
definition.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/stpncpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strcpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power7.S: Likewise.
* sysdeps/powerpc/powerpc64/multiarch/strncpy-power8.S: Likewise.
* sysdeps/powerpc/powerpc64/power7/strncpy.S: Set a default
function name if not defined.
* sysdeps/powerpc/powerpc64/power8/strcpy.S: Likewise.
* sysdeps/powerpc/powerpc64/power8/strncpy.S: Likewise.
This patch optimizes strncpy for power7 for unaligned source or
destination address. The source or destination address is aligned
to doubleword and data is shifted based on the alignment and
added with the previous loaded data to be written as a doubleword.
For each load, cmpb instruction is used for faster null check.
The new optimization shows 10 to 70% of performance improvement
for longer string though it does not show big difference on string
size less than 16 due to additional checks.Hence this new algorithm
is restricted to string greater than 16.
The optimization is achieved by following techniques:
> data alignment [gain from aligned memory access on read/write]
> POWER7 gains performance with loop unrolling/unwinding
[gain by reduction of branch penalty].
> zero padding done by calling optimized memset
