nir: Implement __intrinsic_load_ssbo

v2:
- Fix ssbo loads with boolean variables.

v3:
- Simplify the changes (Kristian)

Reviewed-by: Connor Abbott <connor.w.abbott@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>

src/glsl/nir/glsl_to_nir.cpp

@@ -651,6 +651,8 @@ nir_visitor::visit(ir_call *ir)
          op = nir_intrinsic_image_samples;
       } else if (strcmp(ir->callee_name(), "__intrinsic_store_ssbo") == 0) {
          op = nir_intrinsic_store_ssbo;
+      } else if (strcmp(ir->callee_name(), "__intrinsic_load_ssbo") == 0) {
+         op = nir_intrinsic_load_ssbo;
       } else {
          unreachable("not reached");
       }
@@ -791,6 +793,71 @@ nir_visitor::visit(ir_call *ir)
          nir_instr_insert_after_cf_list(this->cf_node_list, &instr->instr);
          break;
       }
+      case nir_intrinsic_load_ssbo: {
+         exec_node *param = ir->actual_parameters.get_head();
+         ir_rvalue *block = ((ir_instruction *)param)->as_rvalue();
+
+         param = param->get_next();
+         ir_rvalue *offset = ((ir_instruction *)param)->as_rvalue();
+
+         /* Check if we need the indirect version */
+         ir_constant *const_offset = offset->as_constant();
+         if (!const_offset) {
+            op = nir_intrinsic_load_ssbo_indirect;
+            ralloc_free(instr);
+            instr = nir_intrinsic_instr_create(shader, op);
+            instr->src[1] = evaluate_rvalue(offset);
+            instr->const_index[0] = 0;
+            dest = &instr->dest;
+         } else {
+            instr->const_index[0] = const_offset->value.u[0];
+         }
+
+         instr->src[0] = evaluate_rvalue(block);
+
+         const glsl_type *type = ir->return_deref->var->type;
+         instr->num_components = type->vector_elements;
+
+         /* Setup destination register */
+         nir_ssa_dest_init(&instr->instr, &instr->dest,
+                           type->vector_elements, NULL);
+
+         /* Insert the created nir instruction now since in the case of boolean
+          * result we will need to emit another instruction after it
+          */
+         nir_instr_insert_after_cf_list(this->cf_node_list, &instr->instr);
+
+         /*
+          * In SSBO/UBO's, a true boolean value is any non-zero value, but we
+          * consider a true boolean to be ~0. Fix this up with a != 0
+          * comparison.
+          */
+         if (type->base_type == GLSL_TYPE_BOOL) {
+            nir_load_const_instr *const_zero =
+               nir_load_const_instr_create(shader, 1);
+            const_zero->value.u[0] = 0;
+            nir_instr_insert_after_cf_list(this->cf_node_list,
+                                           &const_zero->instr);
+
+            nir_alu_instr *load_ssbo_compare =
+               nir_alu_instr_create(shader, nir_op_ine);
+            load_ssbo_compare->src[0].src.is_ssa = true;
+            load_ssbo_compare->src[0].src.ssa = &instr->dest.ssa;
+            load_ssbo_compare->src[1].src.is_ssa = true;
+            load_ssbo_compare->src[1].src.ssa = &const_zero->def;
+            for (unsigned i = 0; i < type->vector_elements; i++)
+               load_ssbo_compare->src[1].swizzle[i] = 0;
+            nir_ssa_dest_init(&load_ssbo_compare->instr,
+                              &load_ssbo_compare->dest.dest,
+                              type->vector_elements, NULL);
+            load_ssbo_compare->dest.write_mask = (1 << type->vector_elements) - 1;
+            nir_instr_insert_after_cf_list(this->cf_node_list,
+                                           &load_ssbo_compare->instr);
+            dest = &load_ssbo_compare->dest.dest;
+         }
+
+         break;
+      }
       default:
          unreachable("not reached");
       }

src/glsl/nir/nir_intrinsics.h

@@ -200,7 +200,7 @@ SYSTEM_VALUE(user_clip_plane, 4, 1) /* const_index[0] is user_clip_plane[idx] */
 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) */
+LOAD(ssbo, 1, 1, NIR_INTRINSIC_CAN_ELIMINATE)
 
 /*
  * Stores work the same way as loads, except now the first register input is

src/glsl/nir/nir_lower_phis_to_scalar.c

@@ -94,6 +94,8 @@ is_phi_src_scalarizable(nir_phi_src *src,
       case nir_intrinsic_load_uniform_indirect:
       case nir_intrinsic_load_ubo:
       case nir_intrinsic_load_ubo_indirect:
+      case nir_intrinsic_load_ssbo:
+      case nir_intrinsic_load_ssbo_indirect:
       case nir_intrinsic_load_input:
       case nir_intrinsic_load_input_indirect:
          return true;