nir: Add an alignment to nir_intrinsic_load_constant

In f1883cc73d we tried to pass through alignments from load_constant
intrinsics when rewriting them to load_ubo in iris.  However, those
intrinsics don't have ALIGN_MUL or ALIGN_OFFSET indices.  It's easy
enough to add them.  We just call the size/align function on the vector
type at the end of our deref chain and use the alignment returned from
there.  It's possible we could do better by walking the whole deref
chain but this should be good enough.

Fixes: f1883cc73d "iris: Set alignments on cbuf0 and constant reads"
Closes: #2739
Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4468>

src/compiler/nir/nir_intrinsics.py

@@ -747,7 +747,8 @@ load("shared", 1, [BASE, ALIGN_MUL, ALIGN_OFFSET], [CAN_ELIMINATE])
 # src[] = { offset }.
 load("push_constant", 1, [BASE, RANGE], [CAN_ELIMINATE, CAN_REORDER])
 # src[] = { offset }.
-load("constant", 1, [BASE, RANGE], [CAN_ELIMINATE, CAN_REORDER])
+load("constant", 1, [BASE, RANGE, ALIGN_MUL, ALIGN_OFFSET],
+     [CAN_ELIMINATE, CAN_REORDER])
 # src[] = { address }.
 load("global", 1, [ACCESS, ALIGN_MUL, ALIGN_OFFSET], [CAN_ELIMINATE])
 # src[] = { address }.

src/compiler/nir/nir_opt_large_constants.c

@@ -75,11 +75,15 @@ build_constant_load(nir_builder *b, nir_deref_instr *deref,
    size_align(var->type, &var_size, &var_align);
    assert(var->data.location % var_align == 0);
 
+   UNUSED unsigned deref_size, deref_align;
+   size_align(deref->type, &deref_size, &deref_align);
+
    nir_intrinsic_instr *load =
       nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_constant);
    load->num_components = num_components;
    nir_intrinsic_set_base(load, var->data.location);
    nir_intrinsic_set_range(load, var_size);
+   nir_intrinsic_set_align(load, deref_align, 0);
    load->src[0] = nir_src_for_ssa(nir_build_deref_offset(b, deref, size_align));
    nir_ssa_dest_init(&load->instr, &load->dest,
                      num_components, bit_size, NULL);

src/compiler/nir/nir_validate.c

@@ -575,6 +575,7 @@ validate_intrinsic_instr(nir_intrinsic_instr *instr, validate_state *state)
    case nir_intrinsic_load_shared:
    case nir_intrinsic_load_global:
    case nir_intrinsic_load_scratch:
+   case nir_intrinsic_load_constant:
       /* These memory load operations must have alignments */
       validate_assert(state,
          util_is_power_of_two_nonzero(nir_intrinsic_align_mul(instr)));
@@ -589,7 +590,6 @@ validate_intrinsic_instr(nir_intrinsic_instr *instr, validate_state *state)
    case nir_intrinsic_load_output:
    case nir_intrinsic_load_per_vertex_output:
    case nir_intrinsic_load_push_constant:
-   case nir_intrinsic_load_constant:
       /* All memory load operations must load at least a byte */
       validate_assert(state, nir_dest_bit_size(instr->dest) >= 8);
       break;