Earmark extra space for VSX.

Backend specific optimization for PPC VSX reads 16 bytes, whereas arm neon /
sse2 only reads <= 8 bytes. Although the extra bytes read are actually never
used, this is not a warrant for groping around.  Fixed by allocating more when
building for VSX. This is reported by asan.

Also note - PPC does have assembly that loads 64-bit content from memory - lxsdx
loads one 64-bit doubleword (whereas lxvd2x loads two 64-bit doubleword) from
memory. However, we only have "vec_vsx_ld" builtins that mapped to lxvd2x, no
builtins to lxsdx. The only way to access lxsdx is through inline assembly,
which does not fit well in the origin paradigm.

Refer:
  vsx:
    vpx_tm_predictor_4x4_vsx @ third_party/libvpx/git_root/vpx_dsp/ppc/intrapred_vsx.c
  neon:
    vpx_tm_predictor_4x4_neon @ third_party/libvpx/git_root/vpx_dsp/arm/intrapred_neon_asm.asm
  sse2:
    tm_predictor_4x4 @ third_party/libvpx/git_root/vpx_dsp/x86/intrapred_sse2.asm

BUG=b/63112600

Tested:
  asan tests passed.

Change-Id: I5f74b56e35c05b67851de8b5530aece213f2ce9d

2 files changed, 19 insertions, 1 deletions

diff --git a/vp8/common/reconintra.c b/vp8/common/reconintra.c
index 986074ec7..8e2094da8 100644
--- a/vp8/common/reconintra.c
+++ b/vp8/common/reconintra.c
@@ -71,8 +71,16 @@ void vp8_build_intra_predictors_mbuv_s(
     unsigned char *uleft, unsigned char *vleft, int left_stride,
     unsigned char *upred_ptr, unsigned char *vpred_ptr, int pred_stride) {
   MB_PREDICTION_MODE uvmode = x->mode_info_context->mbmi.uv_mode;
+#if HAVE_VSX
+  /* Power PC implementation uses "vec_vsx_ld" to read 16 bytes from
+     uleft_col and vleft_col. Play it safe by reserving enough stack
+     space here. */
+  unsigned char uleft_col[16];
+  unsigned char vleft_col[16];
+#else
   unsigned char uleft_col[8];
   unsigned char vleft_col[8];
+#endif
   int i;
   intra_pred_fn fn;
 
diff --git a/vp8/common/reconintra4x4.c b/vp8/common/reconintra4x4.c
index 7852cf9da..64d33a287 100644
--- a/vp8/common/reconintra4x4.c
+++ b/vp8/common/reconintra4x4.c
@@ -40,7 +40,15 @@ void vp8_intra4x4_predict(unsigned char *above, unsigned char *yleft,
                           int left_stride, B_PREDICTION_MODE b_mode,
                           unsigned char *dst, int dst_stride,
                           unsigned char top_left) {
-  unsigned char Aboveb[12], *Above = Aboveb + 4;
+/* Power PC implementation uses "vec_vsx_ld" to read 16 bytes from
+   Above (aka, Aboveb + 4). Play it safe by reserving enough stack
+   space here. Similary for "Left". */
+#if HAVE_VSX
+  unsigned char Aboveb[20];
+#else
+  unsigned char Aboveb[12];
+#endif
+  unsigned char *Above = Aboveb + 4;
 #if HAVE_NEON
   // Neon intrinsics are unable to load 32 bits, or 4 8 bit values. Instead, it
   // over reads but does not use the extra 4 values.
@@ -50,6 +58,8 @@ void vp8_intra4x4_predict(unsigned char *above, unsigned char *yleft,
   // indeed read, they are not used.
   vp8_zero_array(Left, 8);
 #endif  // VPX_WITH_ASAN
+#elif HAVE_VSX
+  unsigned char Left[16];
 #else
   unsigned char Left[4];
 #endif  // HAVE_NEON