bpo-2506: Experiment with adding a "-X noopt" flag

Include/coreconfig.h

@@ -49,6 +49,7 @@ typedef struct {
 
     const char *allocator;  /* Memory allocator: PYTHONMALLOC */
     int dev_mode;           /* PYTHONDEVMODE, -X dev */
+    int noopt_mode;         /* -X noopt */
 
     /* Enable faulthandler?
        Set to 1 by -X faulthandler and PYTHONFAULTHANDLER. -1 means unset. */

Modules/_testcapimodule.c

@@ -4687,6 +4687,8 @@ get_coreconfig(PyObject *self, PyObject *Py_UNUSED(args))
              FROM_STRING(config->allocator));
     SET_ITEM("dev_mode",
              PyLong_FromLong(config->dev_mode));
+    SET_ITEM("noopt_mode",
+             PyLong_FromLong(config->noopt_mode));
     SET_ITEM("faulthandler",
              PyLong_FromLong(config->faulthandler));
     SET_ITEM("tracemalloc",

Programs/_testembed.c

@@ -320,6 +320,7 @@ dump_config(void)
     printf("allocator = %s\n", config->allocator);
 
     printf("dev_mode = %i\n", config->dev_mode);
+    printf("noopt_mode = %i\n", config->noopt_mode);
     printf("faulthandler = %i\n", config->faulthandler);
     printf("tracemalloc = %i\n", config->tracemalloc);
     printf("import_time = %i\n", config->import_time);

Python/compile.c

@@ -27,6 +27,7 @@
 #include "node.h"
 #include "ast.h"
 #include "code.h"
+#include "internal/pystate.h"
 #include "symtable.h"
 #include "opcode.h"
 #include "wordcode_helpers.h"
@@ -158,6 +159,7 @@ struct compiler {
     PyCompilerFlags *c_flags;
 
     int c_optimize;              /* optimization level */
+    int c_noopt;
     int c_interactive;           /* true if in interactive mode */
     int c_nestlevel;
 
@@ -186,7 +188,7 @@ static int compiler_visit_slice(struct compiler *, slice_ty,
                                 expr_context_ty);
 
 static int inplace_binop(struct compiler *, operator_ty);
-static int expr_constant(expr_ty);
+static int expr_constant(struct compiler *, expr_ty);
 
 static int compiler_with(struct compiler *, stmt_ty, int);
 static int compiler_async_with(struct compiler *, stmt_ty, int);
@@ -300,6 +302,7 @@ PyAST_CompileObject(mod_ty mod, PyObject *filename, PyCompilerFlags *flags,
     PyCodeObject *co = NULL;
     PyCompilerFlags local_flags;
     int merged;
+    const _PyCoreConfig *conf = &_PyInterpreterState_GET_UNSAFE()->core_config;
 
     if (!__doc__) {
         __doc__ = PyUnicode_InternFromString("__doc__");
@@ -330,8 +333,14 @@ PyAST_CompileObject(mod_ty mod, PyObject *filename, PyCompilerFlags *flags,
     c.c_optimize = (optimize == -1) ? Py_OptimizeFlag : optimize;
     c.c_nestlevel = 0;
 
-    if (!_PyAST_Optimize(mod, arena, c.c_optimize)) {
-        goto finally;
+    if (conf->noopt_mode) {
+        c.c_noopt = 1;
+    }
+    else {
+        c.c_noopt = 0;
+        if (!_PyAST_Optimize(mod, arena, c.c_optimize)) {
+            goto finally;
+        }
     }
 
     c.c_st = PySymtable_BuildObject(mod, filename, c.c_future);
@@ -2365,7 +2374,7 @@ compiler_if(struct compiler *c, stmt_ty s)
     if (end == NULL)
         return 0;
 
-    constant = expr_constant(s->v.If.test);
+    constant = expr_constant(c, s->v.If.test);
     /* constant = 0: "if 0"
      * constant = 1: "if 1", "if 2", ...
      * constant = -1: rest */
@@ -2478,7 +2487,8 @@ static int
 compiler_while(struct compiler *c, stmt_ty s)
 {
     basicblock *loop, *orelse, *end, *anchor = NULL;
-    int constant = expr_constant(s->v.While.test);
+
+    int constant = expr_constant(c, s->v.While.test);
 
     if (constant == 0) {
         if (s->v.While.orelse)
@@ -4205,8 +4215,11 @@ compiler_visit_keyword(struct compiler *c, keyword_ty k)
  */
 
 static int
-expr_constant(expr_ty e)
+expr_constant(struct compiler *c, expr_ty e)
 {
+    if (c->c_noopt) {
+        return -1;
+    }
     if (e->kind == Constant_kind) {
         return PyObject_IsTrue(e->v.Constant.value);
     }
@@ -5387,9 +5400,15 @@ makecode(struct compiler *c, struct assembler *a)
     if (flags < 0)
         goto error;
 
-    bytecode = PyCode_Optimize(a->a_bytecode, consts, names, a->a_lnotab);
-    if (!bytecode)
-        goto error;
+    if (!c->c_noopt) {
+        bytecode = PyCode_Optimize(a->a_bytecode, consts, names, a->a_lnotab);
+        if (!bytecode)
+            goto error;
+    }
+    else {
+        bytecode = a->a_bytecode;
+        Py_INCREF(bytecode);
+    }
 
     tmp = PyList_AsTuple(consts); /* PyCode_New requires a tuple */
     if (!tmp)

Python/coreconfig.c

@@ -295,6 +295,7 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
     COPY_ATTR(_install_importlib);
     COPY_ATTR(allocator);
     COPY_ATTR(dev_mode);
+    COPY_ATTR(noopt_mode);
     COPY_ATTR(faulthandler);
     COPY_ATTR(tracemalloc);
     COPY_ATTR(import_time);
@@ -945,6 +946,10 @@ config_read_complex_options(_PyCoreConfig *config)
     {
         config->dev_mode = 1;
     }
+    if (config_get_xoption(config, L"noopt"))
+    {
+        config->noopt_mode = 1;
+    }
 
     _PyInitError err;
     if (config->tracemalloc < 0) {

Python/sysmodule.c

@@ -2060,6 +2060,7 @@ static PyStructSequence_Field flags_fields[] = {
     {"hash_randomization",      "-R"},
     {"isolated",                "-I"},
     {"dev_mode",                "-X dev"},
+    {"noopt_mode",              "-X noopt"},
     {"utf8_mode",               "-X utf8"},
     {0}
 };
@@ -2101,6 +2102,7 @@ make_flags(void)
     SetFlag(config->use_hash_seed == 0 || config->hash_seed != 0);
     SetFlag(config->isolated);
     PyStructSequence_SET_ITEM(seq, pos++, PyBool_FromLong(config->dev_mode));
+    PyStructSequence_SET_ITEM(seq, pos++, PyBool_FromLong(config->noopt_mode));
     SetFlag(config->utf8_mode);
 #undef SetFlag