nir/intrinsics: Add a second const index to load_uniform

In the i965 backend, we want to be able to "pull apart" the uniforms and
push some of them into the shader through a different path.  In order to do
this effectively, we need to know which variable is actually being referred
to by a given uniform load.  Previously, it was completely flattened by
nir_lower_io which made things difficult.  This adds more information to
the intrinsic to make this easier for us.

Reviewed-by: Kenneth Graunke <[email protected]>

3 files changed, 19 insertions, 13 deletions

diff --git a/src/glsl/nir/nir_intrinsics.h b/src/glsl/nir/nir_intrinsics.h
index 6c7a61a8477..ed309b602c2 100644
--- a/src/glsl/nir/nir_intrinsics.h
+++ b/src/glsl/nir/nir_intrinsics.h
@@ -141,11 +141,17 @@ SYSTEM_VALUE(sample_mask_in, 1)
 SYSTEM_VALUE(invocation_id, 1)
 
 /*
- * The first and only index is the base address to load from.  Indirect
- * loads have an additional register input, which is added to the constant
- * address to compute the final address to load from.  For UBO's (and
- * SSBO's), the first source is the (possibly constant) UBO buffer index
- * and the indirect (if it exists) is the second source.
+ * The format of the indices depends on the type of the load.  For uniforms,
+ * the first index is the base address and the second index is an offset that
+ * should be added to the base address.  (This way you can determine in the
+ * back-end which variable is being accessed even in an array.)  For inputs,
+ * the one and only index corresponds to the attribute slot.  UBO loads also
+ * have a single index which is the base address to load from.
+ *
+ * UBO loads have a (possibly constant) source which is the UBO buffer index.
+ * For each type of load, the _indirect variant has one additional source
+ * (the second in the case of UBO's) that is the is an indirect to be added to
+ * the constant address or base offset to compute the final offset.
  *
  * For vector backends, the address is in terms of one vec4, and so each array
  * element is +4 scalar components from the previous array element. For scalar
@@ -153,14 +159,14 @@ SYSTEM_VALUE(invocation_id, 1)
  * elements begin immediately after the previous array element.
  */
 
-#define LOAD(name, extra_srcs, flags) \
-   INTRINSIC(load_##name, extra_srcs, ARR(1), true, 0, 0, 1, flags) \
+#define LOAD(name, extra_srcs, indices, flags) \
+   INTRINSIC(load_##name, extra_srcs, ARR(1), true, 0, 0, indices, flags) \
    INTRINSIC(load_##name##_indirect, extra_srcs + 1, ARR(1, 1), \
-             true, 0, 0, 1, flags)
+             true, 0, 0, indices, flags)
 
-LOAD(uniform, 0, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
-LOAD(ubo, 1, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
-LOAD(input, 0, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+LOAD(uniform, 0, 2, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+LOAD(ubo, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+LOAD(input, 0, 1, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
 /* LOAD(ssbo, 1, 0) */
 
 /*
diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index b32f8a75e73..ad51d80fd09 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -1504,7 +1504,7 @@ fs_visitor::nir_emit_intrinsic(const fs_builder &bld, nir_intrinsic_instr *instr
       has_indirect = true;
       /* fallthrough */
    case nir_intrinsic_load_uniform: {
-      unsigned index = instr->const_index[0];
+      unsigned index = instr->const_index[0] + instr->const_index[1];
 
       fs_reg uniform_reg;
       if (index < num_direct_uniforms) {
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
index 4f689dff1ba..9e52229190e 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
@@ -570,7 +570,7 @@ vec4_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
       has_indirect = true;
       /* fallthrough */
    case nir_intrinsic_load_uniform: {
-      int uniform = instr->const_index[0];
+      int uniform = instr->const_index[0] + instr->const_index[1];
 
       dest = get_nir_dest(instr->dest);