scratch/bytecode-speedup 7875ce7365 1/2: Don't crash on unbalanced unwinds in debug mode

[Mattias Engdegård]

branch: scratch/bytecode-speedup
commit 7875ce7365403522c6aa53c0ac892a6edb7403bd
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Don't crash on unbalanced unwinds in debug mode
    
    * src/bytecode.c (exec_byte_code):
    Restore the previous graceful error (instead of a hard crash) when the
    bytecode doesn't unwind properly, but only when building with
    debugging (NDEBUG not defined, checking enabled, or BYTE_CODE_SAFE
    enabled).
---
 src/bytecode.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/bytecode.c b/src/bytecode.c
index 41455629cb..0bca2546f7 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -1588,10 +1588,17 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object 
vector, Lisp_Object maxdepth,
 
  exit:
 
+#if BYTE_CODE_SAFE || !defined NDEBUG
+  if (SPECPDL_INDEX () != count)
+    {
+      /* Binds and unbinds are supposed to be compiled balanced.  */
+      if (SPECPDL_INDEX () > count)
+       unbind_to (count, Qnil);
+      error ("binding stack not balanced (serious byte compiler bug)");
+    }
+#endif
   /* The byte code should have been properly pinned.  */
   eassert (SDATA (bytestr) == bytestr_data);
-  /* Binds and unbinds are supposed to be compiled balanced.  */
-  eassert (SPECPDL_INDEX () == count);
 
   Lisp_Object result = TOP;
   SAFE_FREE ();