[Mesa-dev] [PATCH] llvmpipe: fix arguments order given to vec_andc

[Oded Gabbay]

This patch fixes a classic "confuse the enemy" bug.

_mm_andnot_si128 (SSE) and vec_andc (VMX) do the same operation, but the
arguments are opposite.

_mm_andnot_si128 performs "r = (~a) & b" while
vec_andc performs "r = a & (~b)"

To make sure this error won't return in another place, I added a wrapper
function, vec_andnot_si128, in u_pwr8.h, which makes the swap inside.

Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
---
 src/gallium/auxiliary/util/u_pwr8.h         | 6 ++++++
 src/gallium/drivers/llvmpipe/lp_setup_tri.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/gallium/auxiliary/util/u_pwr8.h b/src/gallium/auxiliary/util/u_pwr8.h
index 1eca6d6..ffd9f92 100644
--- a/src/gallium/auxiliary/util/u_pwr8.h
+++ b/src/gallium/auxiliary/util/u_pwr8.h
@@ -153,6 +153,12 @@ vec_mullo_epi32 (__m128i a, __m128i b)
    return v;
 }
 
+static inline __m128i
+vec_andnot_si128 (__m128i a, __m128i b)
+{
+   return vec_andc (b, a);
+}
+
 static inline void
 transpose4_epi32(const __m128i * restrict a,
                  const __m128i * restrict b,
diff --git a/src/gallium/drivers/llvmpipe/lp_setup_tri.c b/src/gallium/drivers/llvmpipe/lp_setup_tri.c
index aa24176..907129d 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_tri.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup_tri.c
@@ -556,7 +556,7 @@ do_triangle_ccw(struct lp_setup_context *setup,
 
       /* Calculate trivial reject values:
        */
-      eo = vec_sub_epi32(vec_andc(dcdy_neg_mask, dcdy),
+      eo = vec_sub_epi32(vec_andnot_si128(dcdy_neg_mask, dcdy),
                          vec_and(dcdx_neg_mask, dcdx));
 
       /* ei = _mm_sub_epi32(_mm_sub_epi32(dcdy, dcdx), eo); */
-- 
2.5.0