py: Implement proper context save/restore for eval/exec; factor code.

This has benefits all round: code factoring for parse/compile/execute,
proper context save/restore for exec, allow to sepcify globals/locals
for eval, and reduced ROM usage by >100 bytes on stmhal and unix.

Also, the call to mp_parse_compile_execute is tail call optimised for
the import code, so it doesn't increase stack memory usage.

py/builtinevex.c

@@ -40,66 +40,34 @@
 #include "runtime.h"
 #include "builtin.h"
 
-STATIC mp_obj_t parse_compile_execute(mp_obj_t o_in, mp_parse_input_kind_t parse_input_kind) {
+STATIC mp_obj_t eval_exec_helper(mp_uint_t n_args, const mp_obj_t *args, mp_parse_input_kind_t parse_input_kind) {
     mp_uint_t str_len;
-    const char *str = mp_obj_str_get_data(o_in, &str_len);
+    const char *str = mp_obj_str_get_data(args[0], &str_len);
 
     // create the lexer
     mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_string_gt_, str, str_len, 0);
-    qstr source_name = mp_lexer_source_name(lex);
 
-    // parse the string
-    mp_parse_error_kind_t parse_error_kind;
-    mp_parse_node_t pn = mp_parse(lex, parse_input_kind, &parse_error_kind);
-
-    if (pn == MP_PARSE_NODE_NULL) {
-        // parse error; raise exception
-        mp_obj_t exc = mp_parse_make_exception(lex, parse_error_kind);
-        mp_lexer_free(lex);
-        nlr_raise(exc);
-    }
-
-    mp_lexer_free(lex);
-
-    // compile the string
-    mp_obj_t module_fun = mp_compile(pn, source_name, MP_EMIT_OPT_NONE, false);
-
-    // check if there was a compile error
-    if (mp_obj_is_exception_instance(module_fun)) {
-        nlr_raise(module_fun);
-    }
-
-    // complied successfully, execute it
-    return mp_call_function_0(module_fun);
-}
-
-STATIC mp_obj_t mp_builtin_eval(mp_obj_t o_in) {
-    return parse_compile_execute(o_in, MP_PARSE_EVAL_INPUT);
-}
-
-MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_eval_obj, mp_builtin_eval);
-
-STATIC mp_obj_t mp_builtin_exec(uint n_args, const mp_obj_t *args) {
-    // Unconditional getting/setting assumes that these operations
-    // are cheap, which is the case when this comment was written.
-    mp_obj_dict_t *old_globals = mp_globals_get();
-    mp_obj_dict_t *old_locals = mp_locals_get();
+    // work out the context
+    mp_obj_dict_t *globals = mp_globals_get();
+    mp_obj_dict_t *locals = mp_locals_get();
     if (n_args > 1) {
-        mp_obj_t globals = args[1];
-        mp_obj_t locals;
+        globals = args[1];
         if (n_args > 2) {
             locals = args[2];
         } else {
             locals = globals;
         }
-        mp_globals_set(globals);
-        mp_locals_set(locals);
     }
-    mp_obj_t res = parse_compile_execute(args[0], MP_PARSE_FILE_INPUT);
-    // TODO if the above call throws an exception, then we never get to reset the globals/locals
-    mp_globals_set(old_globals);
-    mp_locals_set(old_locals);
-    return res;
+
+    return mp_parse_compile_execute(lex, parse_input_kind, globals, locals);
+}
+
+STATIC mp_obj_t mp_builtin_eval(mp_uint_t n_args, const mp_obj_t *args) {
+    return eval_exec_helper(n_args, args, MP_PARSE_EVAL_INPUT);
 }
+MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_eval_obj, 1, 3, mp_builtin_eval);
 
+STATIC mp_obj_t mp_builtin_exec(mp_uint_t n_args, const mp_obj_t *args) {
+    return eval_exec_helper(n_args, args, MP_PARSE_FILE_INPUT);
+}
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_exec_obj, 1, 3, mp_builtin_exec);

py/builtinimport.c

@@ -111,56 +111,14 @@ STATIC void do_load(mp_obj_t module_obj, vstr_t *file) {
         nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ImportError, "No module named '%s'", vstr_str(file)));
     }
 
-    qstr source_name = mp_lexer_source_name(lex);
-
-    // save the old context
-    mp_obj_dict_t *old_locals = mp_locals_get();
-    mp_obj_dict_t *old_globals = mp_globals_get();
-
-    // set the new context
-    mp_locals_set(mp_obj_module_get_globals(module_obj));
-    mp_globals_set(mp_obj_module_get_globals(module_obj));
     #if MICROPY_PY___FILE__
-    mp_store_attr(module_obj, MP_QSTR___file__, mp_obj_new_str(vstr_str(file), vstr_len(file), false));
+    qstr source_name = mp_lexer_source_name(lex);
+    mp_store_attr(module_obj, MP_QSTR___file__, MP_OBJ_NEW_QSTR(source_name));
     #endif
 
-    // parse the imported script
-    mp_parse_error_kind_t parse_error_kind;
-    mp_parse_node_t pn = mp_parse(lex, MP_PARSE_FILE_INPUT, &parse_error_kind);
-
-    if (pn == MP_PARSE_NODE_NULL) {
-        // parse error; clean up and raise exception
-        mp_obj_t exc = mp_parse_make_exception(lex, parse_error_kind);
-        mp_lexer_free(lex);
-        mp_locals_set(old_locals);
-        mp_globals_set(old_globals);
-        nlr_raise(exc);
-    }
-
-    mp_lexer_free(lex);
-
-    // compile the imported script
-    mp_obj_t module_fun = mp_compile(pn, source_name, MP_EMIT_OPT_NONE, false);
-
-    if (mp_obj_is_exception_instance(module_fun)) {
-        mp_locals_set(old_locals);
-        mp_globals_set(old_globals);
-        nlr_raise(module_fun);
-    }
-
-    // complied successfully, execute it
-    nlr_buf_t nlr;
-    if (nlr_push(&nlr) == 0) {
-        mp_call_function_0(module_fun);
-        nlr_pop();
-    } else {
-        // exception; restore context and re-raise same exception
-        mp_locals_set(old_locals);
-        mp_globals_set(old_globals);
-        nlr_raise(nlr.ret_val);
-    }
-    mp_locals_set(old_locals);
-    mp_globals_set(old_globals);
+    // parse, compile and execute the module in its context
+    mp_obj_dict_t *mod_globals = mp_obj_module_get_globals(module_obj);
+    mp_parse_compile_execute(lex, MP_PARSE_FILE_INPUT, mod_globals, mod_globals);
 }
 
 mp_obj_t mp_builtin___import__(mp_uint_t n_args, mp_obj_t *args) {

py/compile.h

@@ -35,3 +35,6 @@ enum {
 
 // the compiler will free the parse tree (pn) before it returns
 mp_obj_t mp_compile(mp_parse_node_t pn, qstr source_file, uint emit_opt, bool is_repl);
+
+// this is implemented in runtime.c
+mp_obj_t mp_parse_compile_execute(mp_lexer_t *lex, mp_parse_input_kind_t parse_input_kind, mp_obj_dict_t *globals, mp_obj_dict_t *locals);

py/runtime.c

@@ -24,6 +24,7 @@
  * THE SOFTWARE.
  */
 
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <assert.h>
@@ -46,6 +47,9 @@
 #include "smallint.h"
 #include "objgenerator.h"
 #include "lexer.h"
+#include "parse.h"
+#include "parsehelper.h"
+#include "compile.h"
 #include "stackctrl.h"
 
 #if 0 // print debugging info
@@ -1153,6 +1157,54 @@ void mp_globals_set(mp_obj_dict_t *d) {
     dict_globals = d;
 }
 
+// this is implemented in this file so it can optimise access to locals/globals
+mp_obj_t mp_parse_compile_execute(mp_lexer_t *lex, mp_parse_input_kind_t parse_input_kind, mp_obj_dict_t *globals, mp_obj_dict_t *locals) {
+    // parse the string
+    mp_parse_error_kind_t parse_error_kind;
+    mp_parse_node_t pn = mp_parse(lex, parse_input_kind, &parse_error_kind);
+
+    if (pn == MP_PARSE_NODE_NULL) {
+        // parse error; raise exception
+        mp_obj_t exc = mp_parse_make_exception(lex, parse_error_kind);
+        mp_lexer_free(lex);
+        nlr_raise(exc);
+    }
+
+    qstr source_name = mp_lexer_source_name(lex);
+    mp_lexer_free(lex);
+
+    // save context and set new context
+    mp_obj_dict_t *old_globals = mp_globals_get();
+    mp_obj_dict_t *old_locals = mp_locals_get();
+    mp_globals_set(globals);
+    mp_locals_set(locals);
+
+    // compile the string
+    mp_obj_t module_fun = mp_compile(pn, source_name, MP_EMIT_OPT_NONE, false);
+
+    // check if there was a compile error
+    if (mp_obj_is_exception_instance(module_fun)) {
+        mp_globals_set(old_globals);
+        mp_locals_set(old_locals);
+        nlr_raise(module_fun);
+    }
+
+    // complied successfully, execute it
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_obj_t ret = mp_call_function_0(module_fun);
+        nlr_pop();
+        mp_globals_set(old_globals);
+        mp_locals_set(old_locals);
+        return ret;
+    } else {
+        // exception; restore context and re-raise same exception
+        mp_globals_set(old_globals);
+        mp_locals_set(old_locals);
+        nlr_raise(nlr.ret_val);
+    }
+}
+
 void *m_malloc_fail(size_t num_bytes) {
     DEBUG_printf("memory allocation failed, allocating " UINT_FMT " bytes\n", num_bytes);
     nlr_raise((mp_obj_t)&mp_const_MemoryError_obj);