pythongh-93678: extract 'struct cfg' from the compiler so that the CFG can be manipulated directly

Author: iritkatriel

Python/compile.c

@@ -9613,8 +9613,8 @@ unpack_instruction(PyObject *instr, int *label, int *opcode, int *oparg,
     return 0;
 }
 
-static basicblock *
-instructions_to_cfg(PyObject *instructions)
+static int
+instructions_to_cfg(PyObject *instructions, cfg_builder *g)
 {
     assert(PyList_Check(instructions));
 
@@ -9623,16 +9623,17 @@ instructions_to_cfg(PyObject *instructions)
     basicblock **label2block = (basicblock **)PyMem_Malloc(sizeof(basicblock *) * max_labels);
     if (!label2block) {
         PyErr_NoMemory();
+        return -1;
     }
     memset(label2block, 0, sizeof(basicblock *) * max_labels);
 
-    basicblock *entryblock = new_basicblock();
-    if (entryblock == NULL) {
+    g->block_list = NULL;
+    basicblock *block = cfg_builder_new_block(g);
+    if (block == NULL) {
         goto error;
     }
-    basicblock *current_block = entryblock;
+    g->curblock = g->cfg_entryblock = block;
 
-    bool start_new_block = false;
     for (Py_ssize_t i = 0; i < num_insts; i++) {
         PyObject *instr_tuple = PyList_GET_ITEM(instructions, i);
         int label, opcode, oparg, target;
@@ -9642,7 +9643,7 @@ instructions_to_cfg(PyObject *instructions)
         }
         if (label >= max_labels || target >= max_labels) {
             PyErr_SetString(PyExc_ValueError, "label is out of range");
-            return NULL;
+            goto error;
         }
         basicblock *new_block = NULL;
         if (label > 0 && label2block[label] != NULL) {
@@ -9652,44 +9653,37 @@ instructions_to_cfg(PyObject *instructions)
              */
             assert(new_block->b_iused == 0);
         }
-        else if (start_new_block || label > 0) {
-            new_block = new_basicblock();
+        else if (label > 0) {
+            new_block = cfg_builder_new_block(g);
             if (new_block == NULL) {
                 goto error;
             }
-            if (label > 0) {
-                assert(label < max_labels);
-                label2block[label] = new_block;
-            }
+            assert(label < max_labels);
+            label2block[label] = new_block;
         }
         if (new_block) {
-            current_block->b_next = new_block;
-            current_block = new_block;
-            start_new_block = false;
+            cfg_builder_use_next_block(g, new_block);
         }
         basicblock *target_block = NULL;
         if (target > 0) {
             target_block = label2block[target];
             if (target_block == NULL) {
-                target_block = new_basicblock();
+                target_block = cfg_builder_new_block(g);
                 if (target_block == NULL) {
                     goto error;
                 }
                 label2block[target] = target_block;
             }
         }
-        if (!basicblock_addop(current_block, opcode, oparg, target_block, &loc)) {
+        if (!cfg_builder_addop(g, opcode, oparg, target_block, loc)) {
             goto error;
         }
-        if (IS_TERMINATOR_OPCODE(opcode)) {
-            start_new_block = true;
-        }
     }
     PyMem_Free(label2block);
-    return entryblock;
+    return 0;
 error:
     PyMem_Free(label2block);
-    return NULL;
+    return -1;
 }
 
 static PyObject *
@@ -9742,16 +9736,20 @@ _PyCompile_OptimizeCfg(PyObject *instructions, PyObject *consts)
     if (const_cache == NULL) {
         return NULL;
     }
-    basicblock *entryblock = instructions_to_cfg(instructions);
-    if (optimize_cfg(entryblock, consts, const_cache)) {
+    cfg_builder g;
+    instructions_to_cfg(instructions, &g);
+
+    if (optimize_cfg(g.cfg_entryblock, consts, const_cache)) {
         goto error;
     }
-    PyObject *optimized_instructions = cfg_to_instructions(entryblock);
+    PyObject *optimized_instructions = cfg_to_instructions(g.cfg_entryblock);
     if (optimized_instructions == NULL) {
         goto error;
     }
+    cfg_builder_free(&g);
     return PyTuple_Pack(2, optimized_instructions, consts);
 error:
+    cfg_builder_free(&g);
     return NULL;
 }