Decompiler: propagate labels through nested statement lists

angr/analyses/decompiler/structured_codegen/c.py

@@ -906,21 +906,38 @@ class CStatements(CStatement):
         self.addr = addr
 
     def c_repr_chunks(self, indent=0, asexpr=False):
+        yield from self._c_repr_chunks(indent=indent, asexpr=asexpr, terminate_trailing_label=True)
+
+    def _c_repr_chunks(self, indent=0, asexpr=False, *, terminate_trailing_label):
         indent_str = self.indent_str(indent)
         if self.codegen.display_block_addrs:
             yield indent_str, None
             yield f"/* Block {hex(self.addr) if self.addr is not None else 'unknown'} */", None
             yield "\n", None
         for stmt in self.statements:
-            yield from stmt.c_repr_chunks(indent=indent, asexpr=asexpr)
+            if isinstance(stmt, CStatements):
+                # CStatements may be a transparent sequence nested inside another sequence. A label at the end of
+                # the inner sequence still labels the next statement in the outer sequence.
+                yield from stmt._c_repr_chunks(indent=indent, asexpr=asexpr, terminate_trailing_label=False)
+            else:
+                yield from stmt.c_repr_chunks(indent=indent, asexpr=asexpr)
             if asexpr:
                 yield ", ", None
-        if not asexpr and self.statements and isinstance(self.statements[-1], CLabel):
-            # A C label prefixes a statement; it is not a complete statement itself. Finish a trailing label run
-            # locally so that the next statement in an outer sequence cannot become its labeled statement.
+        if not asexpr and terminate_trailing_label and isinstance(self._last_nonempty_statement(), CLabel):
+            # A C label prefixes a statement; it is not a complete statement itself. Finish it only at the boundary
+            # of the enclosing sequence, after looking through transparent nested sequences.
             yield indent_str, None
             yield ";\n", None
 
+    def _last_nonempty_statement(self) -> CStatement | None:
+        for stmt in reversed(self.statements):
+            if isinstance(stmt, CStatements):
+                stmt = stmt._last_nonempty_statement()
+                if stmt is None:
+                    continue
+            return stmt
+        return None
+
 
 class CAILBlock(CStatement):
     """

tests/analyses/decompiler/test_structured_codegen_c.py

@@ -57,6 +57,32 @@ def test_trailing_label_run_has_one_null_statement():
     assert _render(statements, indent=4) == "LABEL_400000:\nLABEL_400010:\n    ;\n"
 
 
+def test_nested_trailing_label_prefixes_next_outer_statement():
+    codegen = _codegen()
+    statements = CStatements(
+        [
+            CStatements([CLabel("LABEL_400000", codegen=codegen)], codegen=codegen),
+            CReturn(None, codegen=codegen),
+        ],
+        codegen=codegen,
+    )
+
+    assert _render(statements) == "LABEL_400000:\nreturn;\n"
+
+
+def test_nested_terminal_label_has_null_statement():
+    codegen = _codegen()
+    statements = CStatements(
+        [
+            CStatements([CLabel("LABEL_400000", codegen=codegen)], codegen=codegen),
+            CStatements([], codegen=codegen),
+        ],
+        codegen=codegen,
+    )
+
+    assert _render(statements, indent=4) == "LABEL_400000:\n    ;\n"
+
+
 def test_trailing_label_does_not_capture_outer_statement():
     codegen = _codegen()
     conditional = CIfElse(