vpermps (added here) makes this very easy,
with an index controlling what 32-bit values go where.
A index of the form {0,2,4,6|?,?,?,?} will put the 4 low 32-bit halves
of 4 64-bit values in lanes 0,1,2,3. We can use that twice to get all 8
low halves, then our new vperm2f128 to put them together. Conveniently
vpermps can also load directly from memory:
vpermps (%rdi), {0,2,4,6|?,?,?,?}, lo
vpermps 32(%rdi), {0,2,4,6|?,?,?,?}, hi
vperm2f128 0x20, lo,hi, dst
We don't care what those top four indices are for load64_lo, so we'll
use them as the indices for load64_hi. That makes the full index
{0,2,4,6|1,3,5,7}, and load64_hi will just vpermf128 the other 128-bits
of lo/hi:
vpermps (%rdi), {?,?,?,?|1,3,5,7}, lo
vpermps 32(%rdi), {?,?,?,?|1,3,5,7}, hi
vperm2f128 0x31, lo,hi, dst
vpermps needs its index in a register, so we use a temporary for that.
Our logical lo can alias dst, and hi can alias that index, so it's just
one extra temporary register in the end.
Change-Id: Ie6a4efbf12ddada45dd09c0f580fa7350cf3019e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/305171
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
184f601346