add code-comments in variance_svp64_real.s on how to use sv.bc/ctr/all

diff --git a/media/video/libvpx/variance_svp64_real.s b/media/video/libvpx/variance_svp64_real.s
index 046f68beb6d5197d5e7b220746af7ed503697a56..664297643087fc7a1ea3aab1032e3b431a4a0dcd 100644 (file)
--- a/media/video/libvpx/variance_svp64_real.s
+++ b/media/video/libvpx/variance_svp64_real.s
@@ -32,7 +32,9 @@ variance_svp64_real:
        li      row, 0                          # Set row to zero
        sldi    src_stride, src_stride, 1       # strides are for 16-bit elements
        sldi    ref_stride, ref_stride, 1       # we need to increase by bytes
+    # XXX this can go, no need to divide by 4
        srdi    width, width, 2                 # We load groups of 4
+    # XXX this to be moved inside (top of) L2 loop
        setvl   0,0,4,0,1,1                     # Set VL to 4 elements
 
 .L1:   # outer loop: for (r=0; r < h; r++)
@@ -41,6 +43,7 @@ variance_svp64_real:
        mr      ctr, width                      # Set up CTR to width/4 -1 on each row
        mtctr   ctr                             # Set up counter
 .L2:   # inner loop: for (c=0; c < w; c += 4)
+       # XXX setvl     30,0,4,0,1,1                    # Set MAXVL=4, and r30=VL=MIN(CTR,MAXVL)
        # Load 4 elements from src_ptr and ref_ptr
        sv.lha  *src, 0(src_col)                # Load 4 ints from (src_ptr)
        sv.lha  *ref, 0(ref_col)                # Load 4 ints from (ref_ptr)
@@ -56,6 +59,7 @@ variance_svp64_real:
 
        addi    src_col, src_col, 8             # Increment src, ref by 8 bytes
        addi    ref_col, ref_col, 8
+    # XXX replace with "sv.bc/ctr/all 16,*0,L2" which does "CTR -= VL"
        bdnz    .L2                             # Loop until CTR is zero
 
        add     src_ptr, src_ptr, src_stride    # Advance src_ptr by src_stride