nir/loop_analyze: use nir_alu_src to track the invariant

This helps reduce the amount of abstraction in this pass and allows
us to retain more information about the src such as any swizzles.
Retaining the swizzle information is required for a bugfix in a
following patch.

Fixes: 6772a17a ("nir: Add a loop analysis pass")
Tested-by: Brian Paul <brianp@vmware.com>

src/compiler/nir/nir_loop_analyze.c

@@ -60,7 +60,7 @@ typedef struct {
 typedef struct nir_basic_induction_var {
    nir_op alu_op;                           /* The type of alu-operation    */
    nir_loop_variable *alu_def;              /* The def of the alu-operation */
-   nir_loop_variable *invariant;            /* The invariant alu-operand    */
+   nir_alu_src *invariant;                  /* The invariant alu-src        */
    nir_loop_variable *def_outside_loop;     /* The phi-src outside the loop */
 } nir_basic_induction_var;
 
@@ -356,7 +356,7 @@ compute_induction_information(loop_info_state *state)
                   /* Is one of the operands const, and the other the phi */
                   if (alu->src[i].src.ssa->parent_instr->type == nir_instr_type_load_const &&
                       alu->src[1-i].src.ssa == &phi->dest.ssa)
-                     biv->invariant = get_loop_var(alu->src[i].src.ssa, state);
+                     biv->invariant = &alu->src[i];
                }
             }
          }
@@ -364,7 +364,7 @@ compute_induction_information(loop_info_state *state)
 
       if (biv->alu_def && biv->def_outside_loop && biv->invariant &&
           is_var_constant(biv->def_outside_loop)) {
-         assert(is_var_constant(biv->invariant));
+         assert(is_var_constant(get_loop_var(biv->invariant->src.ssa, state)));
          biv->alu_def->type = basic_induction;
          biv->alu_def->ind = biv;
          var->type = basic_induction;
@@ -960,8 +960,8 @@ find_trip_count(loop_info_state *state)
                                     def->parent_instr)->value;
 
       nir_const_value *step_val =
-         nir_instr_as_load_const(basic_ind->ind->invariant->def->
-                                    parent_instr)->value;
+         nir_instr_as_load_const(basic_ind->ind->invariant->src.ssa->
+                                 parent_instr)->value;
 
       int iterations = calculate_iterations(initial_val, step_val,
                                             &limit_val,