Fix a bug in vp9_iht16x16_256_add_neon()

This bug was introduced in 88c23864.

BUG=webm:1403

Change-Id: If96fd6f102be6b9bda866e55e574257287746f4a

2 files changed, 34 insertions, 36 deletions

diff --git a/vp9/common/arm/neon/vp9_iht16x16_add_neon.c b/vp9/common/arm/neon/vp9_iht16x16_add_neon.c
index fc9824ae9..a7d5a53c7 100644
--- a/vp9/common/arm/neon/vp9_iht16x16_add_neon.c
+++ b/vp9/common/arm/neon/vp9_iht16x16_add_neon.c
@@ -221,30 +221,10 @@ static void iadst16x16_256_add_half1d(const void *const input, int16_t *output,
   x[15] = sub_dct_const_round_shift_low_8(s13, s15);
 
   // stage 4
-  {
-    const int16x8_t sum = vaddq_s16(x[2], x[3]);
-    const int16x8_t sub = vsubq_s16(x[2], x[3]);
-    x[2] = iadst_half_butterfly_neg_neon(sum, c_16_n16_8_24);
-    x[3] = iadst_half_butterfly_pos_neon(sub, c_16_n16_8_24);
-  }
-  {
-    const int16x8_t sum = vaddq_s16(x[7], x[6]);
-    const int16x8_t sub = vsubq_s16(x[7], x[6]);
-    x[6] = iadst_half_butterfly_pos_neon(sum, c_16_n16_8_24);
-    x[7] = iadst_half_butterfly_pos_neon(sub, c_16_n16_8_24);
-  }
-  {
-    const int16x8_t sum = vaddq_s16(x[11], x[10]);
-    const int16x8_t sub = vsubq_s16(x[11], x[10]);
-    x[10] = iadst_half_butterfly_pos_neon(sum, c_16_n16_8_24);
-    x[11] = iadst_half_butterfly_pos_neon(sub, c_16_n16_8_24);
-  }
-  {
-    const int16x8_t sum = vaddq_s16(x[14], x[15]);
-    const int16x8_t sub = vsubq_s16(x[14], x[15]);
-    x[14] = iadst_half_butterfly_neg_neon(sum, c_16_n16_8_24);
-    x[15] = iadst_half_butterfly_pos_neon(sub, c_16_n16_8_24);
-  }
+  iadst_half_butterfly_neg_neon(&x[3], &x[2], c_16_n16_8_24);
+  iadst_half_butterfly_pos_neon(&x[7], &x[6], c_16_n16_8_24);
+  iadst_half_butterfly_pos_neon(&x[11], &x[10], c_16_n16_8_24);
+  iadst_half_butterfly_neg_neon(&x[15], &x[14], c_16_n16_8_24);
 
   out[0] = x[0];
   out[1] = vnegq_s16(x[8]);
diff --git a/vp9/common/arm/neon/vp9_iht_neon.h b/vp9/common/arm/neon/vp9_iht_neon.h
index 965eff36b..b09b96a4d 100644
--- a/vp9/common/arm/neon/vp9_iht_neon.h
+++ b/vp9/common/arm/neon/vp9_iht_neon.h
@@ -74,22 +74,40 @@ static INLINE void iadst_half_butterfly_neon(int16x8_t *const x,
   x[1] = dct_const_round_shift_low_8(t1);
 }
 
-static INLINE int16x8_t iadst_half_butterfly_neg_neon(const int16x8_t in,
-                                                      const int16x4_t c) {
-  int32x4_t t[2];
+static INLINE void iadst_half_butterfly_neg_neon(int16x8_t *const x0,
+                                                 int16x8_t *const x1,
+                                                 const int16x4_t c) {
+  // Don't add/sub before multiply, which will overflow in iadst8.
+  const int32x4_t x0_lo = vmull_lane_s16(vget_low_s16(*x0), c, 1);
+  const int32x4_t x0_hi = vmull_lane_s16(vget_high_s16(*x0), c, 1);
+  const int32x4_t x1_lo = vmull_lane_s16(vget_low_s16(*x1), c, 1);
+  const int32x4_t x1_hi = vmull_lane_s16(vget_high_s16(*x1), c, 1);
+  int32x4_t t0[2], t1[2];
 
-  t[0] = vmull_lane_s16(vget_low_s16(in), c, 1);
-  t[1] = vmull_lane_s16(vget_high_s16(in), c, 1);
-  return dct_const_round_shift_low_8(t);
+  t0[0] = vaddq_s32(x0_lo, x1_lo);
+  t0[1] = vaddq_s32(x0_hi, x1_hi);
+  t1[0] = vsubq_s32(x0_lo, x1_lo);
+  t1[1] = vsubq_s32(x0_hi, x1_hi);
+  *x1 = dct_const_round_shift_low_8(t0);
+  *x0 = dct_const_round_shift_low_8(t1);
 }
 
-static INLINE int16x8_t iadst_half_butterfly_pos_neon(const int16x8_t in,
-                                                      const int16x4_t c) {
-  int32x4_t t[2];
+static INLINE void iadst_half_butterfly_pos_neon(int16x8_t *const x0,
+                                                 int16x8_t *const x1,
+                                                 const int16x4_t c) {
+  // Don't add/sub before multiply, which will overflow in iadst8.
+  const int32x4_t x0_lo = vmull_lane_s16(vget_low_s16(*x0), c, 0);
+  const int32x4_t x0_hi = vmull_lane_s16(vget_high_s16(*x0), c, 0);
+  const int32x4_t x1_lo = vmull_lane_s16(vget_low_s16(*x1), c, 0);
+  const int32x4_t x1_hi = vmull_lane_s16(vget_high_s16(*x1), c, 0);
+  int32x4_t t0[2], t1[2];
 
-  t[0] = vmull_lane_s16(vget_low_s16(in), c, 0);
-  t[1] = vmull_lane_s16(vget_high_s16(in), c, 0);
-  return dct_const_round_shift_low_8(t);
+  t0[0] = vaddq_s32(x0_lo, x1_lo);
+  t0[1] = vaddq_s32(x0_hi, x1_hi);
+  t1[0] = vsubq_s32(x0_lo, x1_lo);
+  t1[1] = vsubq_s32(x0_hi, x1_hi);
+  *x1 = dct_const_round_shift_low_8(t0);
+  *x0 = dct_const_round_shift_low_8(t1);
 }
 
 static INLINE void iadst_butterfly_lane_0_1_neon(const int16x8_t in0,