ir3: Fix LDC offset units

I had missed that LDC actually uses vec4 units for its offset. This
means that we have to create a new instruction, and lower it in
ir3_nir_lower_io_offsets, similar to the existing SSBO instructions.
Unfortunately we can't assume that loads are always vec4-aligned, so we
have to use the alignment information that NIR gives us. Unfortunately,
it's currently woefully inadequate, and will have to be fixed to give us
good codegen in the future.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4568>

src/compiler/nir/nir_intrinsics.py

@@ -802,6 +802,12 @@ intrinsic("ssbo_atomic_xor_ir3",        src_comp=[1, 1, 1, 1],    dest_comp=1)
 intrinsic("ssbo_atomic_exchange_ir3",   src_comp=[1, 1, 1, 1],    dest_comp=1)
 intrinsic("ssbo_atomic_comp_swap_ir3",  src_comp=[1, 1, 1, 1, 1], dest_comp=1)
 
+# IR3-specific instruction for UBO loads using the ldc instruction. The second
+# source is the indirect offset, in units of four dwords. The base is a
+# component offset, in dword units.
+intrinsic("load_ubo_ir3", src_comp=[1, 1], bit_sizes=[32], dest_comp=0, indices=[BASE],
+          flags=[CAN_REORDER, CAN_ELIMINATE])
+
 # System values for freedreno geometry shaders.
 system_value("vs_primitive_stride_ir3", 1)
 system_value("vs_vertex_stride_ir3", 1)