cleanup simple loop filter

move some things around, reorder some instructions

constant 0 is used several times. load it once per call in horiz,
once per loop in vert.

separate saturating instructions to avoid stalls.

just use one usub8 call to set GE flags, rather than uqsub8 followed by
usub8 w/ 0

document some stalls for further consideration

Change-Id: Ic3877e0ddbe314bb8a17fd5db73501a7d64570ec

1 files changed, 49 insertions, 63 deletions

diff --git a/vp8/common/arm/armv6/simpleloopfilter_v6.asm b/vp8/common/arm/armv6/simpleloopfilter_v6.asm
index 011808430..3a700cd59 100644
--- a/vp8/common/arm/armv6/simpleloopfilter_v6.asm
+++ b/vp8/common/arm/armv6/simpleloopfilter_v6.asm
@@ -55,8 +55,8 @@ pstep       RN  r1
 ;stack  const char *thresh,
 ;stack  int  count
 
-;Note: All 16 elements in flimit are equal. So, in the code, only one load is needed
-;for flimit. Same way applies to limit and thresh.
+; All 16 elements in flimit are equal. So, in the code, only one load is needed
+; for flimit. Same applies to limit. thresh is not used in simple looopfilter
 
 ;-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 |vp8_loop_filter_simple_horizontal_edge_armv6| PROC
@@ -65,23 +65,19 @@ pstep       RN  r1
 
     ldr         r12, [r3]                   ; limit
     ldr         r3, [src, -pstep, lsl #1]   ; p1
-
-    ldr         r9, [sp, #40]               ; count for 8-in-parallel
     ldr         r4, [src, -pstep]           ; p0
-
-    ldr         r7, [r2]                    ; flimit
     ldr         r5, [src]                   ; q0
-    ldr         r2, c0x80808080
-
     ldr         r6, [src, pstep]            ; q1
-
+    ldr         r7, [r2]                    ; flimit
+    ldr         r2, c0x80808080
+    ldr         r9, [sp, #40]               ; count for 8-in-parallel
     uadd8       r7, r7, r7                  ; flimit * 2
     mov         r9, r9, lsl #1              ; double the count. we're doing 4 at a time
     uadd8       r12, r7, r12                ; flimit * 2 + limit
-    mov         lr, #0
+    mov         lr, #0                      ; need 0 in a couple places
 
 |simple_hnext8|
-    ; vp8_simple_filter_mask() function
+    ; vp8_simple_filter_mask()
 
     uqsub8      r7, r3, r6                  ; p1 - q1
     uqsub8      r8, r6, r3                  ; q1 - p1
@@ -89,58 +85,50 @@ pstep       RN  r1
     uqsub8      r11, r5, r4                 ; q0 - p0
     orr         r8, r8, r7                  ; abs(p1 - q1)
     orr         r10, r10, r11               ; abs(p0 - q0)
-    uhadd8      r8, r8, lr                  ; abs(p1 - q2) >> 1
     uqadd8      r10, r10, r10               ; abs(p0 - q0) * 2
-    ; STALL waiting on r10
+    uhadd8      r8, r8, lr                  ; abs(p1 - q2) >> 1
     uqadd8      r10, r10, r8                ; abs(p0 - q0)*2 + abs(p1 - q1)/2
-    ; STALL waiting on r10
     mvn         r8, #0
-    uqsub8      r10, r10, r12               ; compare to flimit. need to do this twice because uqsub8 doesn't set GE flags
-                                            ; and usub8 doesn't saturate
-    usub8       r10, lr, r10                ; set GE flags for each byte
+    usub8       r10, r12, r10               ; compare to flimit. usub8 sets GE flags
     sel         r10, r8, lr                 ; filter mask: F or 0
     cmp         r10, #0
-    beq         simple_hskip_filter         ; skip filtering if we're &ing with 0s. would just write out the same values
+    beq         simple_hskip_filter         ; skip filtering if all masks are 0x00
 
-    ;vp8_simple_filter() function
+    ;vp8_simple_filter()
 
     eor         r3, r3, r2                  ; p1 offset to convert to a signed value
     eor         r6, r6, r2                  ; q1 offset to convert to a signed value
     eor         r4, r4, r2                  ; p0 offset to convert to a signed value
     eor         r5, r5, r2                  ; q0 offset to convert to a signed value
 
-    qsub8       r3, r3, r6                  ; vp8_signed_char_clamp(p1-q1)
-    qsub8       r6, r5, r4                  ; vp8_signed_char_clamp(q0-p0)
-    qadd8       r3, r3, r6                  ; += q0-p0
-    qadd8       r3, r3, r6                  ; += q0-p0
-    qadd8       r3, r3, r6                  ; p1-q1 + 3*(q0-p0))
-    and         r3, r3, r10                 ; &= mask
-
+    qsub8       r3, r3, r6                  ; vp8_filter = p1 - q1
+    qsub8       r6, r5, r4                  ; q0 - p0
+    qadd8       r3, r3, r6                  ; += q0 - p0
     ldr         r7, c0x04040404
+    qadd8       r3, r3, r6                  ; += q0 - p0
     ldr         r8, c0x03030303
-
-    ;save bottom 3 bits so that we round one side +4 and the other +3
-    qadd8       r7 , r3 , r7                ; Filter1 (r3) = vp8_signed_char_clamp(vp8_filter+4)
-    qadd8       r8 , r3 , r8                ; Filter2 (r8) = vp8_signed_char_clamp(vp8_filter+3)
-
-    mov         r3, #0
-    shadd8      r7 , r7 , r3
-    shadd8      r8 , r8 , r3
-    shadd8      r7 , r7 , r3
-    shadd8      r8 , r8 , r3
-    shadd8      r7 , r7 , r3                ; Filter1 >>= 3
-    shadd8      r8 , r8 , r3                ; Filter2 >>= 3
-
-
-    qsub8       r5 ,r5, r7                  ; u = vp8_signed_char_clamp(q0 - Filter1)
-    qadd8       r4, r4, r8                  ; u = vp8_signed_char_clamp(p0 + Filter2)
+    qadd8       r3, r3, r6                  ; vp8_filter = p1-q1 + 3*(q0-p0))
+    ;STALL
+    and         r3, r3, r10                 ; vp8_filter &= mask
+
+    qadd8       r7 , r3 , r7                ; Filter1 = vp8_filter + 4
+    qadd8       r8 , r3 , r8                ; Filter2 = vp8_filter + 3
+
+    shadd8      r7 , r7 , lr
+    shadd8      r8 , r8 , lr
+    shadd8      r7 , r7 , lr
+    shadd8      r8 , r8 , lr
+    shadd8      r7 , r7 , lr                ; Filter1 >>= 3
+    shadd8      r8 , r8 , lr                ; Filter2 >>= 3
+
+    qsub8       r5 ,r5, r7                  ; u = q0 - Filter1
+    qadd8       r4, r4, r8                  ; u = p0 + Filter2
     eor         r5, r5, r2                  ; *oq0 = u^0x80
     str         r5, [src]                   ; store oq0 result
     eor         r4, r4, r2                  ; *op0 = u^0x80
     str         r4, [src, -pstep]           ; store op0 result
 
 |simple_hskip_filter|
-
     subs        r9, r9, #1
     addne       src, src, #4                ; next row
 
@@ -204,9 +192,8 @@ pstep       RN  r1
     uhadd8      r7, r7, r8                  ; abs(p1 - q1) / 2
     uqadd8      r7, r7, r9                  ; abs(p0 - q0)*2 + abs(p1 - q1)/2
     mvn         r10, #0                     ; r10 == -1
-    uqsub8      r7, r7, r12                 ; compare to flimit
 
-    usub8       r7, r8, r7
+    usub8       r7, r12, r7                 ; compare to flimit
     sel         lr, r10, r8                 ; filter mask
 
     cmp         lr, #0
@@ -218,35 +205,34 @@ pstep       RN  r1
     eor         r4, r4, r2                  ; p0 offset to convert to a signed value
     eor         r5, r5, r2                  ; q0 offset to convert to a signed value
 
-    qsub8       r3, r3, r6                  ; vp8_filter (r3) = vp8_signed_char_clamp(p1-q1)
-    qsub8       r6, r5, r4                  ; vp8_filter = vp8_signed_char_clamp(vp8_filter + 3 * ( q0 - p0))
+    qsub8       r3, r3, r6                  ; vp8_filter = p1 - q1
+    qsub8       r6, r5, r4                  ; q0 - p0
 
-    qadd8       r3, r3, r6
-    ldr         r8, c0x03030303             ; r8 = 3
+    qadd8       r3, r3, r6                  ; vp8_filter += q0 - p0
+    ldr         r9, c0x03030303             ; r9 = 3
 
-    qadd8       r3, r3, r6
+    qadd8       r3, r3, r6                  ; vp8_filter += q0 - p0
     ldr         r7, c0x04040404
 
-    qadd8       r3, r3, r6
+    qadd8       r3, r3, r6                  ; vp8_filter = p1-q1 + 3*(q0-p0))
+    ;STALL
     and         r3, r3, lr                  ; vp8_filter &= mask
 
-    ;save bottom 3 bits so that we round one side +4 and the other +3
-    qadd8       r8 , r3 , r8                ; Filter2 (r8) = vp8_signed_char_clamp(vp8_filter+3)
-    qadd8       r3 , r3 , r7                ; Filter1 (r3) = vp8_signed_char_clamp(vp8_filter+4)
+    qadd8       r9 , r3 , r9                ; Filter2 = vp8_filter + 3
+    qadd8       r3 , r3 , r7                ; Filter1 = vp8_filter + 4
 
-    mov         r7, #0
-    shadd8      r8 , r8 , r7                ; Filter2 >>= 3
-    shadd8      r3 , r3 , r7                ; Filter1 >>= 3
-    shadd8      r8 , r8 , r7
-    shadd8      r3 , r3 , r7
-    shadd8      r8 , r8 , r7                ; r8: filter2
-    shadd8      r3 , r3 , r7                ; r7: filter1
+    shadd8      r9 , r9 , r8
+    shadd8      r3 , r3 , r8
+    shadd8      r9 , r9 , r8
+    shadd8      r3 , r3 , r8
+    shadd8      r9 , r9 , r8                ; Filter2 >>= 3
+    shadd8      r3 , r3 , r8                ; Filter1 >>= 3
 
     ;calculate output
     sub         src, src, pstep, lsl #2
 
-    qadd8       r4, r4, r8                  ; u = vp8_signed_char_clamp(p0 + Filter2)
-    qsub8       r5, r5, r3                  ; u = vp8_signed_char_clamp(q0 - Filter1)
+    qadd8       r4, r4, r9                  ; u = p0 + Filter2
+    qsub8       r5, r5, r3                  ; u = q0 - Filter1
     eor         r4, r4, r2                  ; *op0 = u^0x80
     eor         r5, r5, r2                  ; *oq0 = u^0x80