GH-91409: Don't overwrite valid locations with NOP locations (GH-95067)

Author: brandtbucher

Lib/test/test_compile.py

@@ -1202,6 +1202,44 @@ def test_multiline_assert_rewritten_as_method_call(self):
         tree.body[0] = new_node
         compile(tree, "<test>", "exec")
 
+    def test_push_null_load_global_positions(self):
+        source_template = """
+        import abc, dis
+        import ast as art
+
+        abc = None
+        dix = dis
+        ast = art
+
+        def f():
+        {}
+        """
+        for body in [
+            "    abc.a()",
+            "    art.a()",
+            "    ast.a()",
+            "    dis.a()",
+            "    dix.a()",
+            "    abc[...]()",
+            "    art()()",
+            "   (ast or ...)()",
+            "   [dis]()",
+            "   (dix + ...)()",
+        ]:
+            with self.subTest(body):
+                namespace = {}
+                source = textwrap.dedent(source_template.format(body))
+                exec(source, namespace)
+                code = namespace["f"].__code__
+                self.assertOpcodeSourcePositionIs(
+                    code,
+                    "LOAD_GLOBAL",
+                    line=10,
+                    end_line=10,
+                    column=4,
+                    end_column=7,
+                )
+
 
 class TestExpressionStackSize(unittest.TestCase):
     # These tests check that the computed stack size for a code object

Misc/NEWS.d/next/Core and Builtins/2022-07-20-13-46-01.gh-issue-91409.dhL8Zo.rst

@@ -0,0 +1,2 @@
+Fix incorrect source location info caused by certain optimizations in the
+bytecode compiler.

Python/compile.c

@@ -9278,7 +9278,10 @@ clean_basic_block(basicblock *bb) {
             /* or, if the next instruction has same line number or no line number */
             if (src < bb->b_iused - 1) {
                 int next_lineno = bb->b_instr[src+1].i_loc.lineno;
-                if (next_lineno < 0 || next_lineno == lineno) {
+                if (next_lineno == lineno) {
+                    continue;
+                }
+                if (next_lineno < 0) {
                     bb->b_instr[src+1].i_loc = bb->b_instr[src].i_loc;
                     continue;
                 }