On PowerPC there are 128 bit VSX registers. These registers are half
overlapped with 64 bit floating point registers (FPR). The 64 bit half
of the VXS register that does not overlap with the FPR does not overlap
with any other register class. The FPR are the only subregisters of the
VSX registers but they do not fully cover the 128 bit super register.
This leads to incorrect lane masks being created.
This patch adds phony registers for the other half of the VSX registers
in order to fully cover them and to make sure that the lane masks are
not the same for the VSX and the floating point register.
This patch only adds tests for PowerPC. The purpose of these tests
is to track what code is generated for various vector reductions.
Reviewed By: nemanjai, #powerpc
Differential Revision: https://reviews.llvm.org/D113801
