[Mesa-dev] [PATCH 3/3] i965: Fix scalar VS float[] and vec2[] output arrays.

[Kenneth Graunke]

The scalar VS backend has never handled float[] and vec2[] outputs
correctly (my original code was broken).  Outputs need to be padded
out to vec4 slots.

In fs_visitor::nir_setup_outputs(), we tried to process each vec4 slot
by looping from 0 to ALIGN(type_size_scalar(type), 4) / 4.  However,
this is wrong: type_size_scalar() for a float[2] would return 2, or
for vec2[2] it would return 4.  This looked like a single slot, even
though in reality each array element would be stored in separate vec4
slots.

Because of this bug, outputs[] and output_components[] would not get
initialized for the second element's VARYING_SLOT, which meant
emit_urb_writes() would skip writing them.  Nothing used those values,
and dead code elimination threw a party.

The new type_size_4x() function pads array elements correctly, but
still counts in scalar components, generating correct indices in
store_output intrinsics.

Not observed to fix any Piglit or dEQP tests, but does fix various
tcs-input Piglit tests on a branch that implements tessellation shaders.

Cc: mesa-stable at lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 2 +-
 src/mesa/drivers/dri/i965/brw_nir.c      | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 0e044d0..a290656 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -93,7 +93,7 @@ fs_visitor::nir_setup_outputs()
 
       switch (stage) {
       case MESA_SHADER_VERTEX:
-         for (unsigned int i = 0; i < ALIGN(type_size_scalar(var->type), 4) / 4; i++) {
+         for (int i = 0; i < type_size_4x(var->type) / 4; i++) {
             int output = var->data.location + i;
             this->outputs[output] = offset(reg, bld, 4 * i);
             this->output_components[output] = vector_elements;
diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index 1b4dace..c7f94a6 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -117,7 +117,8 @@ brw_nir_lower_outputs(nir_shader *nir, bool is_scalar)
    case MESA_SHADER_GEOMETRY:
       if (is_scalar) {
          nir_assign_var_locations(&nir->outputs, &nir->num_outputs,
-                                  type_size_scalar);
+                                  type_size_4x);
+         nir_lower_io(nir, nir_var_shader_out, type_size_4x);
       } else {
          nir_foreach_variable(var, &nir->outputs)
             var->data.driver_location = var->data.location;
-- 
2.6.1