nir/i965: use two slots from inputs_read for dvec3/dvec4 vertex input attributes

So far, input_reads was a bitmap tracking which vertex input locations
were being used.

In OpenGL, an attribute bigger than a vec4 (like a dvec3 or dvec4)
consumes just one location, any other small attribute. So we mark the
proper bit in inputs_read, and also the same bit in double_inputs_read
if the attribute is a dvec3/dvec4.

But in Vulkan, this is slightly different: a dvec3/dvec4 attribute
consumes two locations, not just one. And hence two bits would be marked
in inputs_read for the same vertex input attribute.

To avoid handling two different situations in NIR, we just choose the
latest one: in OpenGL, when creating NIR from GLSL/IR, any dvec3/dvec4
vertex input attribute is marked with two bits in the inputs_read bitmap
(and also in the double_inputs_read), and following attributes are
adjusted accordingly.

As example, if in our GLSL/IR shader we have three attributes:

layout(location = 0) vec3  attr0;
layout(location = 1) dvec4 attr1;
layout(location = 2) dvec3 attr2;

then in our NIR shader we put attr0 in location 0, attr1 in locations 1
and 2, and attr2 in location 3 and 4.

Checking carefully, basically we are using slots rather than locations
in NIR.

When emitting the vertices, we do a inverse map to know the
corresponding location for each slot.

v2 (Jason):
- use two slots from inputs_read for dvec3/dvec4 NIR from GLSL/IR.

v3 (Jason):
- Fix commit log error.
- Use ladder ifs and fix braces.
- elements_double is divisible by 2, don't need DIV_ROUND_UP().
- Use if ladder instead of a switch.
- Add comment about hardware restriction in 64bit vertex attributes.

Reviewed-by: Jason Ekstrand <[email protected]>

1 files changed, 1 insertions, 2 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 3775e6c4a09..cea38d86237 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -36,8 +36,7 @@ fs_reg *
 fs_visitor::emit_vs_system_value(int location)
 {
    fs_reg *reg = new(this->mem_ctx)
-      fs_reg(ATTR, 4 * (_mesa_bitcount_64(nir->info->inputs_read) +
-                        _mesa_bitcount_64(nir->info->double_inputs_read)),
+      fs_reg(ATTR, 4 * _mesa_bitcount_64(nir->info->inputs_read),
              BRW_REGISTER_TYPE_D);
    struct brw_vs_prog_data *vs_prog_data = brw_vs_prog_data(prog_data);