gh-92228: disable the compiler's 'small exit block inlining' optimization for blocks that have a line number (GH-94592)

Inlining of code that corresponds to source code lines, can make it hard to distinguish later between code which is only reachable from except handlers, and that which is reachable in normal control flow. This caused problems with the debugger's jump feature.

This PR turns off the inlining optimisation for code which has line numbers. We still inline things like the implicit "return None".

1 files changed, 14 insertions, 0 deletions

diff --git a/Python/compile.c b/Python/compile.c
index 7717689..f36a6e8 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -9224,6 +9224,16 @@ error:
     return -1;
 }
 
+static bool
+basicblock_has_lineno(const basicblock *bb) {
+    for (int i = 0; i < bb->b_iused; i++) {
+        if (bb->b_instr[i].i_loc.lineno > 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /* If this block ends with an unconditional jump to an exit block,
  * then remove the jump and extend this block with the target.
  */
@@ -9240,6 +9250,10 @@ extend_block(basicblock *bb) {
     }
     if (basicblock_exits_scope(last->i_target) && last->i_target->b_iused <= MAX_COPY_SIZE) {
         basicblock *to_copy = last->i_target;
+        if (basicblock_has_lineno(to_copy)) {
+            /* copy only blocks without line number (like implicit 'return None's) */
+            return 0;
+        }
         last->i_opcode = NOP;
         for (int i = 0; i < to_copy->b_iused; i++) {
             int index = basicblock_next_instr(bb);