py/emitnative: Simplify layout and loading of native function prelude.

Now native functions and native generators have similar behaviour: the
first machine-word of their code is an index to get to the prelude.  This
simplifies the handling of these types of functions, and also reduces the
size of the emitted native machine code by no longer requiring special code
at the start of the function to load a pointer to the prelude.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 4 insertions, 11 deletions

diff --git a/py/emitnative.c b/py/emitnative.c
index 5f347799e..6b5c9452a 100644
--- a/py/emitnative.c
+++ b/py/emitnative.c
@@ -253,7 +253,6 @@ struct _emit_t {
     int pass;
 
     bool do_viper_types;
-    bool prelude_offset_uses_u16_encoding;
 
     mp_uint_t local_vtype_alloc;
     vtype_kind_t *local_vtype;
@@ -519,8 +518,11 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
         // work out size of state (locals plus stack)
         emit->n_state = scope->num_locals + scope->stack_size;
 
+        // Store in the first machine-word an index used to the function's prelude.
+        // This is used at runtime by mp_obj_fun_native_get_prelude_ptr().
+        mp_asm_base_data(&emit->as->base, ASM_WORD_SIZE, (uintptr_t)emit->prelude_ptr_index);
+
         if (emit->scope->scope_flags & MP_SCOPE_FLAG_GENERATOR) {
-            mp_asm_base_data(&emit->as->base, ASM_WORD_SIZE, (uintptr_t)emit->prelude_ptr_index);
             mp_asm_base_data(&emit->as->base, ASM_WORD_SIZE, (uintptr_t)emit->start_offset);
             ASM_ENTRY(emit->as, emit->code_state_start);
 
@@ -576,15 +578,6 @@ STATIC void emit_native_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scop
             // Set code_state.fun_bc
             ASM_MOV_LOCAL_REG(emit->as, LOCAL_IDX_FUN_OBJ(emit), REG_PARENT_ARG_1);
 
-            // Set code_state.ip, a pointer to the beginning of the prelude.  This pointer is found
-            // either directly in mp_obj_fun_bc_t.child_table (if there are no children), or in
-            // mp_obj_fun_bc_t.child_table[num_children] (if num_children > 0).
-            ASM_LOAD_REG_REG_OFFSET(emit->as, REG_PARENT_ARG_1, REG_PARENT_ARG_1, OFFSETOF_OBJ_FUN_BC_CHILD_TABLE);
-            if (emit->prelude_ptr_index != 0) {
-                ASM_LOAD_REG_REG_OFFSET(emit->as, REG_PARENT_ARG_1, REG_PARENT_ARG_1, emit->prelude_ptr_index);
-            }
-            emit_native_mov_state_reg(emit, emit->code_state_start + OFFSETOF_CODE_STATE_IP, REG_PARENT_ARG_1);
-
             // Set code_state.n_state (only works on little endian targets due to n_state being uint16_t)
             emit_native_mov_state_imm_via(emit, emit->code_state_start + OFFSETOF_CODE_STATE_N_STATE, emit->n_state, REG_ARG_1);