[Mesa-dev] [PATCH v3 23/42] intel/compiler: fix ddx and ddy for 16-bit float

[Iago Toral Quiroga]

We were assuming 32-bit elements. Also, In SIMD8 we pack 2 vector components
in a single SIMD register, so for example, component Y of a 16-bit vec2
starts is at byte offset 16B. This means that when we compute the offset of
the elements to be differentiated we should not stomp whatever base offset we
have, but instead add to it.

v2
 - Use byte_offset() helper (Jason)
 - Merge the fix for SIMD8: using byte_offset() fixes that too.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net> (v1)
---
 src/intel/compiler/brw_fs_generator.cpp | 37 ++++++++++++-------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/src/intel/compiler/brw_fs_generator.cpp b/src/intel/compiler/brw_fs_generator.cpp
index 5fc6cf5f8cc..d0cc4a6d231 100644
--- a/src/intel/compiler/brw_fs_generator.cpp
+++ b/src/intel/compiler/brw_fs_generator.cpp
@@ -1315,10 +1315,9 @@ fs_generator::generate_ddx(const fs_inst *inst,
       width = BRW_WIDTH_4;
    }
 
-   struct brw_reg src0 = src;
+   struct brw_reg src0 = byte_offset(src, type_sz(src.type));;
    struct brw_reg src1 = src;
 
-   src0.subnr   = sizeof(float);
    src0.vstride = vstride;
    src0.width   = width;
    src0.hstride = BRW_HORIZONTAL_STRIDE_0;
@@ -1337,23 +1336,25 @@ void
 fs_generator::generate_ddy(const fs_inst *inst,
                            struct brw_reg dst, struct brw_reg src)
 {
+   const uint32_t type_size = type_sz(src.type);
+
    if (inst->opcode == FS_OPCODE_DDY_FINE) {
       /* produce accurate derivatives */
       if (devinfo->gen >= 11) {
          src = stride(src, 0, 2, 1);
-         struct brw_reg src_0  = byte_offset(src,  0 * sizeof(float));
-         struct brw_reg src_2  = byte_offset(src,  2 * sizeof(float));
-         struct brw_reg src_4  = byte_offset(src,  4 * sizeof(float));
-         struct brw_reg src_6  = byte_offset(src,  6 * sizeof(float));
-         struct brw_reg src_8  = byte_offset(src,  8 * sizeof(float));
-         struct brw_reg src_10 = byte_offset(src, 10 * sizeof(float));
-         struct brw_reg src_12 = byte_offset(src, 12 * sizeof(float));
-         struct brw_reg src_14 = byte_offset(src, 14 * sizeof(float));
-
-         struct brw_reg dst_0  = byte_offset(dst,  0 * sizeof(float));
-         struct brw_reg dst_4  = byte_offset(dst,  4 * sizeof(float));
-         struct brw_reg dst_8  = byte_offset(dst,  8 * sizeof(float));
-         struct brw_reg dst_12 = byte_offset(dst, 12 * sizeof(float));
+         struct brw_reg src_0  = byte_offset(src,  0 * type_size);
+         struct brw_reg src_2  = byte_offset(src,  2 * type_size);
+         struct brw_reg src_4  = byte_offset(src,  4 * type_size);
+         struct brw_reg src_6  = byte_offset(src,  6 * type_size);
+         struct brw_reg src_8  = byte_offset(src,  8 * type_size);
+         struct brw_reg src_10 = byte_offset(src, 10 * type_size);
+         struct brw_reg src_12 = byte_offset(src, 12 * type_size);
+         struct brw_reg src_14 = byte_offset(src, 14 * type_size);
+
+         struct brw_reg dst_0  = byte_offset(dst,  0 * type_size);
+         struct brw_reg dst_4  = byte_offset(dst,  4 * type_size);
+         struct brw_reg dst_8  = byte_offset(dst,  8 * type_size);
+         struct brw_reg dst_12 = byte_offset(dst, 12 * type_size);
 
          brw_push_insn_state(p);
          brw_set_default_exec_size(p, BRW_EXECUTE_4);
@@ -1380,10 +1381,8 @@ fs_generator::generate_ddy(const fs_inst *inst,
       }
    } else {
       /* replicate the derivative at the top-left pixel to other pixels */
-      struct brw_reg src0 = stride(src, 4, 4, 0);
-      struct brw_reg src1 = stride(src, 4, 4, 0);
-      src0.subnr = 0 * sizeof(float);
-      src1.subnr = 2 * sizeof(float);
+      struct brw_reg src0 = byte_offset(stride(src, 4, 4, 0), 0 * type_size);
+      struct brw_reg src1 = byte_offset(stride(src, 4, 4, 0), 2 * type_size);
 
       brw_ADD(p, dst, negate(src0), src1);
    }
-- 
2.17.1