nir: Add a function for rewriting instruction destinations

Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>

src/glsl/nir/nir.c

@@ -1177,6 +1177,30 @@ nir_if_rewrite_condition(nir_if *if_stmt, nir_src new_src)
    src_add_all_uses(src, NULL, if_stmt);
 }
 
+void
+nir_instr_rewrite_dest(nir_instr *instr, nir_dest *dest, nir_dest new_dest)
+{
+   if (dest->is_ssa) {
+      /* We can only overwrite an SSA destination if it has no uses. */
+      assert(list_empty(&dest->ssa.uses) && list_empty(&dest->ssa.if_uses));
+   } else {
+      list_del(&dest->reg.def_link);
+      if (dest->reg.indirect)
+         src_remove_all_uses(dest->reg.indirect);
+   }
+
+   /* We can't re-write with an SSA def */
+   assert(!new_dest.is_ssa);
+
+   nir_dest_copy(dest, &new_dest, instr);
+
+   dest->reg.parent_instr = instr;
+   list_addtail(&dest->reg.def_link, &new_dest.reg.reg->defs);
+
+   if (dest->reg.indirect)
+      src_add_all_uses(dest->reg.indirect, instr, NULL);
+}
+
 void
 nir_ssa_def_init(nir_instr *instr, nir_ssa_def *def,
                  unsigned num_components, const char *name)

src/glsl/nir/nir.h

@@ -1735,6 +1735,8 @@ bool nir_srcs_equal(nir_src src1, nir_src src2);
 void nir_instr_rewrite_src(nir_instr *instr, nir_src *src, nir_src new_src);
 void nir_instr_move_src(nir_instr *dest_instr, nir_src *dest, nir_src *src);
 void nir_if_rewrite_condition(nir_if *if_stmt, nir_src new_src);
+void nir_instr_rewrite_dest(nir_instr *instr, nir_dest *dest,
+                            nir_dest new_dest);
 
 void nir_ssa_dest_init(nir_instr *instr, nir_dest *dest,
                        unsigned num_components, const char *name);