bpo-44626: Merge basic blocks earlier to enable better handling of exit blocks without line numbers (GH-27138) (GH-27182)

(cherry picked from commit a86f7dae0a)

Lib/test/test_dis.py

@@ -1069,7 +1069,7 @@ expected_opinfo_jumpy = [
   Instruction(opname='JUMP_FORWARD', opcode=110, arg=12, argval=144, argrepr='to 144', offset=118, starts_line=None, is_jump_target=False),
   Instruction(opname='DUP_TOP', opcode=4, arg=None, argval=None, argrepr='', offset=120, starts_line=22, is_jump_target=True),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=2, argval='ZeroDivisionError', argrepr='ZeroDivisionError', offset=122, starts_line=None, is_jump_target=False),
-  Instruction(opname='JUMP_IF_NOT_EXC_MATCH', opcode=121, arg=106, argval=212, argrepr='to 212', offset=124, starts_line=None, is_jump_target=False),
+  Instruction(opname='JUMP_IF_NOT_EXC_MATCH', opcode=121, arg=120, argval=240, argrepr='to 240', offset=124, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=126, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=128, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=130, starts_line=None, is_jump_target=False),
@@ -1078,7 +1078,7 @@ expected_opinfo_jumpy = [
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=1, argval=1, argrepr='', offset=136, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=138, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_EXCEPT', opcode=89, arg=None, argval=None, argrepr='', offset=140, starts_line=None, is_jump_target=False),
-  Instruction(opname='JUMP_FORWARD', opcode=110, arg=22, argval=188, argrepr='to 188', offset=142, starts_line=None, is_jump_target=False),
+  Instruction(opname='JUMP_FORWARD', opcode=110, arg=41, argval=226, argrepr='to 226', offset=142, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_FAST', opcode=124, arg=0, argval='i', argrepr='i', offset=144, starts_line=25, is_jump_target=True),
   Instruction(opname='SETUP_WITH', opcode=143, arg=12, argval=172, argrepr='to 172', offset=146, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=1, argval='dodgy', argrepr='dodgy', offset=148, starts_line=None, is_jump_target=False),
@@ -1092,7 +1092,7 @@ expected_opinfo_jumpy = [
   Instruction(opname='DUP_TOP', opcode=4, arg=None, argval=None, argrepr='', offset=164, starts_line=None, is_jump_target=False),
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=3, argval=3, argrepr='', offset=166, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=168, starts_line=None, is_jump_target=False),
-  Instruction(opname='JUMP_FORWARD', opcode=110, arg=8, argval=188, argrepr='to 188', offset=170, starts_line=None, is_jump_target=False),
+  Instruction(opname='JUMP_FORWARD', opcode=110, arg=20, argval=212, argrepr='to 212', offset=170, starts_line=None, is_jump_target=False),
   Instruction(opname='WITH_EXCEPT_START', opcode=49, arg=None, argval=None, argrepr='', offset=172, starts_line=None, is_jump_target=True),
   Instruction(opname='POP_JUMP_IF_TRUE', opcode=115, arg=89, argval=178, argrepr='to 178', offset=174, starts_line=None, is_jump_target=False),
   Instruction(opname='RERAISE', opcode=119, arg=1, argval=1, argrepr='', offset=176, starts_line=None, is_jump_target=False),
@@ -1101,7 +1101,7 @@ expected_opinfo_jumpy = [
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=182, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_EXCEPT', opcode=89, arg=None, argval=None, argrepr='', offset=184, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=186, starts_line=None, is_jump_target=False),
-  Instruction(opname='POP_BLOCK', opcode=87, arg=None, argval=None, argrepr='', offset=188, starts_line=None, is_jump_target=True),
+  Instruction(opname='POP_BLOCK', opcode=87, arg=None, argval=None, argrepr='', offset=188, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=1, argval='print', argrepr='print', offset=190, starts_line=28, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=10, argval="OK, now we're done", argrepr='"OK, now we\'re done"', offset=192, starts_line=None, is_jump_target=False),
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=1, argval=1, argrepr='', offset=194, starts_line=None, is_jump_target=False),
@@ -1113,7 +1113,21 @@ expected_opinfo_jumpy = [
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=1, argval=1, argrepr='', offset=206, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=208, starts_line=None, is_jump_target=False),
   Instruction(opname='RERAISE', opcode=119, arg=0, argval=0, argrepr='', offset=210, starts_line=None, is_jump_target=False),
-  Instruction(opname='RERAISE', opcode=119, arg=0, argval=0, argrepr='', offset=212, starts_line=22, is_jump_target=True),
+  Instruction(opname='POP_BLOCK', opcode=87, arg=None, argval=None, argrepr='', offset=212, starts_line=25, is_jump_target=True),
+  Instruction(opname='LOAD_GLOBAL', opcode=116, arg=1, argval='print', argrepr='print', offset=214, starts_line=28, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=10, argval="OK, now we're done", argrepr='"OK, now we\'re done"', offset=216, starts_line=None, is_jump_target=False),
+  Instruction(opname='CALL_FUNCTION', opcode=131, arg=1, argval=1, argrepr='', offset=218, starts_line=None, is_jump_target=False),
+  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=220, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=0, argval=None, argrepr='None', offset=222, starts_line=None, is_jump_target=False),
+  Instruction(opname='RETURN_VALUE', opcode=83, arg=None, argval=None, argrepr='', offset=224, starts_line=None, is_jump_target=False),
+  Instruction(opname='POP_BLOCK', opcode=87, arg=None, argval=None, argrepr='', offset=226, starts_line=23, is_jump_target=True),
+  Instruction(opname='LOAD_GLOBAL', opcode=116, arg=1, argval='print', argrepr='print', offset=228, starts_line=28, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=10, argval="OK, now we're done", argrepr='"OK, now we\'re done"', offset=230, starts_line=None, is_jump_target=False),
+  Instruction(opname='CALL_FUNCTION', opcode=131, arg=1, argval=1, argrepr='', offset=232, starts_line=None, is_jump_target=False),
+  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=234, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CONST', opcode=100, arg=0, argval=None, argrepr='None', offset=236, starts_line=None, is_jump_target=False),
+  Instruction(opname='RETURN_VALUE', opcode=83, arg=None, argval=None, argrepr='', offset=238, starts_line=None, is_jump_target=False),
+  Instruction(opname='RERAISE', opcode=119, arg=0, argval=0, argrepr='', offset=240, starts_line=22, is_jump_target=True),
 ]
 
 # One last piece of inspect fodder to check the default line number handling

Lib/test/test_sys_settrace.py

@@ -986,14 +986,29 @@ class TraceTestCase(unittest.TestCase):
             except Exception:
                 pass
 
-        # This doesn't conform to PEP 626
         self.run_and_compare(func,
             [(0, 'call'),
              (1, 'line'),
              (2, 'line'),
              (3, 'line'),
-             (5, 'line'),
-             (5, 'return')])
+             (3, 'return')])
+
+    def test_if_in_if_in_if(self):
+        def func(a=0, p=1, z=1):
+            if p:
+                if a:
+                    if z:
+                        pass
+                    else:
+                        pass
+            else:
+                pass
+
+        self.run_and_compare(func,
+            [(0, 'call'),
+             (1, 'line'),
+             (2, 'line'),
+             (2, 'return')])
 
     def test_early_exit_with(self):
 

Python/compile.c

@@ -6934,10 +6934,11 @@ makecode(struct compiler *c, struct assembler *a, PyObject *consts)
 /* For debugging purposes only */
 #if 0
 static void
-dump_instr(const struct instr *i)
+dump_instr(struct instr *i)
 {
-    const char *jrel = (is_relative_jump(instr)) ? "jrel " : "";
-    const char *jabs = (is_jump(instr) && !is_relative_jump(instr))? "jabs " : "";
+    const char *jrel = (is_relative_jump(i)) ? "jrel " : "";
+    const char *jabs = (is_jump(i) && !is_relative_jump(i))? "jabs " : "";
+
     char arg[128];
 
     *arg = '\0';
@@ -6974,6 +6975,9 @@ optimize_cfg(struct compiler *c, struct assembler *a, PyObject *consts);
 static int
 ensure_exits_have_lineno(struct compiler *c);
 
+static int
+extend_block(basicblock *bb);
+
 static int
 insert_generator_prefix(struct compiler *c, basicblock *entryblock) {
 
@@ -7063,6 +7067,12 @@ assemble(struct compiler *c, int addNone)
         }
     }
 
+    for (basicblock *b = c->u->u_blocks; b != NULL; b = b->b_list) {
+        if (extend_block(b)) {
+            return NULL;
+        }
+    }
+
     if (ensure_exits_have_lineno(c)) {
         return NULL;
     }
@@ -7096,6 +7106,7 @@ assemble(struct compiler *c, int addNone)
     if (consts == NULL) {
         goto error;
     }
+
     if (optimize_cfg(c, &a, consts)) {
         goto error;
     }
@@ -7459,19 +7470,14 @@ optimize_basic_block(struct compiler *c, basicblock *bb, PyObject *consts)
                             goto error;
                         }
                         break;
-                    default:
-                        if (inst->i_target->b_exit && inst->i_target->b_iused <= MAX_COPY_SIZE) {
-                            basicblock *to_copy = inst->i_target;
-                            inst->i_opcode = NOP;
-                            for (i = 0; i < to_copy->b_iused; i++) {
-                                int index = compiler_next_instr(bb);
-                                if (index < 0) {
-                                    return -1;
-                                }
-                                bb->b_instr[index] = to_copy->b_instr[i];
-                            }
-                            bb->b_exit = 1;
-                        }
+                }
+                break;
+            case FOR_ITER:
+                assert (i == bb->b_iused-1);
+                if (target->i_opcode == JUMP_FORWARD) {
+                    if (eliminate_jump_to_jump(bb, inst->i_opcode)) {
+                        goto error;
+                    }
                 }
                 break;
             case ROT_N:
@@ -7501,6 +7507,32 @@ error:
     return -1;
 }
 
+/* If this block ends with an unconditional jump to an exit block,
+ * then remove the jump and extend this block with the target.
+ */
+static int
+extend_block(basicblock *bb) {
+    if (bb->b_iused == 0) {
+        return 0;
+    }
+    struct instr *last = &bb->b_instr[bb->b_iused-1];
+    if (last->i_opcode != JUMP_ABSOLUTE && last->i_opcode != JUMP_FORWARD) {
+        return 0;
+    }
+    if (last->i_target->b_exit && last->i_target->b_iused <= MAX_COPY_SIZE) {
+        basicblock *to_copy = last->i_target;
+        last->i_opcode = NOP;
+        for (int i = 0; i < to_copy->b_iused; i++) {
+            int index = compiler_next_instr(bb);
+            if (index < 0) {
+                return -1;
+            }
+            bb->b_instr[index] = to_copy->b_instr[i];
+        }
+        bb->b_exit = 1;
+    }
+    return 0;
+}
 
 static void
 clean_basic_block(basicblock *bb, int prev_lineno) {