nir: remove parent_instr from nir_register

It's no longer used.

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

src/glsl/nir/nir.c

@@ -57,7 +57,6 @@ reg_create(void *mem_ctx, struct exec_list *list)
 {
    nir_register *reg = ralloc(mem_ctx, nir_register);
 
-   reg->parent_instr = NULL;
    list_inithead(&reg->uses);
    list_inithead(&reg->defs);
    list_inithead(&reg->if_uses);

src/glsl/nir/nir.h

@@ -389,14 +389,6 @@ typedef struct {
     */
    bool is_packed;
 
-   /**
-    * If this pointer is non-NULL then this register has exactly one
-    * definition and that definition dominates all of its uses.  This is
-    * set by the out-of-SSA pass so that backends can get SSA-like
-    * information even once they have gone out of SSA.
-    */
-   struct nir_instr *parent_instr;
-
    /** set of nir_instr's where this register is used (read from) */
    struct list_head uses;
 

src/glsl/nir/nir_from_ssa.c

@@ -496,14 +496,6 @@ rewrite_ssa_def(nir_ssa_def *def, void *void_state)
       reg->name = def->name;
       reg->num_components = def->num_components;
       reg->num_array_elems = 0;
-
-      /* This register comes from an SSA definition that is defined and not
-       * part of a phi-web.  Therefore, we know it has a single unique
-       * definition that dominates all of its uses; we can copy the
-       * parent_instr from the SSA def safely.
-       */
-      if (def->parent_instr->type != nir_instr_type_ssa_undef)
-         reg->parent_instr = def->parent_instr;
    }
 
    nir_ssa_def_rewrite_uses(def, nir_src_for_reg(reg), state->mem_ctx);