Don’t ignore -Wclobbered in eval.c

This fix is also prompted by Emacs bug#71744.
* src/eval.c (CACHEABLE): Remove.  All uses removed.
Do not ignore -Wclobbered.
(internal_lisp_condition_case): Fix violations of the C standard,
where setjmp clobbered oldhandlerlist, var, and clauses.
Rewrite to pacify GCC, by using a sentinel rather than a count,
which GCC incorrectly complained about, and by coalescing some
duplicate code.  If GCC_LINT && __GNUC__ && !__clang__ add a useless
assignment to pacify GCC.

1 files changed, 47 insertions, 62 deletions

diff --git a/src/eval.c b/src/eval.c
index b4103acd28f..ce7b08e894a 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -31,15 +31,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include "pdumper.h"
 #include "atimer.h"
 
-/* CACHEABLE is ordinarily nothing, except it is 'volatile' if
-   necessary to cajole GCC into not warning incorrectly that a
-   variable should be volatile.  */
-#if defined GCC_LINT || defined lint
-# define CACHEABLE volatile
-#else
-# define CACHEABLE /* empty */
-#endif
-
 /* Non-nil means record all fset's and provide's, to be undone
    if the file being autoloaded is not fully loaded.
    They are recorded by being consed onto the front of Vautoload_queue:
@@ -430,7 +421,7 @@ DEFUN ("progn", Fprogn, Sprogn, 0, UNEVALLED, 0,
 usage: (progn BODY...)  */)
   (Lisp_Object body)
 {
-  Lisp_Object CACHEABLE val = Qnil;
+  Lisp_Object val = Qnil;
 
   while (CONSP (body))
     {
@@ -1257,12 +1248,6 @@ usage: (catch TAG BODY...)  */)
   return internal_catch (tag, Fprogn, XCDR (args));
 }
 
-/* Work around GCC bug 61118
-   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61118>.  */
-#if GNUC_PREREQ (4, 9, 0)
-# pragma GCC diagnostic ignored "-Wclobbered"
-#endif
-
 /* Assert that E is true, but do not evaluate E.  Use this instead of
    eassert (E) when E contains variables that might be clobbered by a
    longjmp.  */
@@ -1488,8 +1473,10 @@ Lisp_Object
 internal_lisp_condition_case (Lisp_Object var, Lisp_Object bodyform,
                               Lisp_Object handlers)
 {
-  struct handler *oldhandlerlist = handlerlist;
-  ptrdiff_t CACHEABLE clausenb = 0;
+  struct handler *volatile oldhandlerlist = handlerlist;
+
+  /* The number of non-success handlers, plus 1 for a sentinel.  */
+  ptrdiff_t clausenb = 1;
 
   var = maybe_remove_pos_from_symbol (var);
   CHECK_TYPE (BARE_SYMBOL_P (var), Qsymbolp, var);
@@ -1521,69 +1508,67 @@ internal_lisp_condition_case (Lisp_Object var, Lisp_Object bodyform,
     memory_full (SIZE_MAX);
   Lisp_Object volatile *clauses = alloca (clausenb * sizeof *clauses);
   clauses += clausenb;
+  *--clauses = make_fixnum (0);
   for (Lisp_Object tail = handlers; CONSP (tail); tail = XCDR (tail))
     {
       Lisp_Object tem = XCAR (tail);
       if (!(CONSP (tem) && EQ (XCAR (tem), QCsuccess)))
         *--clauses = tem;
     }
-  for (ptrdiff_t i = 0; i < clausenb; i++)
+  Lisp_Object volatile var_volatile = var;
+  Lisp_Object val, handler_body;
+  for (Lisp_Object volatile *pcl = clauses; ; pcl++)
     {
-      Lisp_Object clause = clauses[i];
+      if (BASE_EQ (*pcl, make_fixnum (0)))
+        {
+          val = eval_sub (bodyform);
+          handlerlist = oldhandlerlist;
+          if (NILP (success_handler))
+            return val;
+#if GCC_LINT && __GNUC__ && !__clang__
+          /* This useless assignment pacifies GCC 14.2.1 x86-64
+             <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21161>.  */
+          var = var_volatile;
+#endif
+          handler_body = XCDR (success_handler);
+          break;
+        }
+      Lisp_Object clause = *pcl;
       Lisp_Object condition = CONSP (clause) ? XCAR (clause) : Qnil;
       if (!CONSP (condition))
         condition = list1 (condition);
       struct handler *c = push_handler (condition, CONDITION_CASE);
+      Lisp_Object volatile *clauses_volatile = clauses;
       if (sys_setjmp (c->jmp))
         {
-          Lisp_Object val = handlerlist->val;
-          Lisp_Object volatile *chosen_clause = clauses;
-          for (struct handler *h = handlerlist->next; h != oldhandlerlist;
-               h = h->next)
+          var = var_volatile;
+          val = handlerlist->val;
+          Lisp_Object volatile *chosen_clause = clauses_volatile;
+          struct handler *oldh = oldhandlerlist;
+          for (struct handler *h = handlerlist->next; h != oldh; h = h->next)
             chosen_clause++;
-          Lisp_Object handler_body = XCDR (*chosen_clause);
-          handlerlist = oldhandlerlist;
-
-          if (NILP (var))
-            return Fprogn (handler_body);
+          handler_body = XCDR (*chosen_clause);
+          handlerlist = oldh;
 
-          Lisp_Object handler_var = var;
-          if (!NILP (Vinternal_interpreter_environment))
-            {
-              val = Fcons (Fcons (var, val),
-                           Vinternal_interpreter_environment);
-              handler_var = Qinternal_interpreter_environment;
-            }
-
-          /* Bind HANDLER_VAR to VAL while evaluating HANDLER_BODY.
-             The unbind_to undoes just this binding; whoever longjumped
-             to us unwound the stack to C->pdlcount before throwing.  */
-          specpdl_ref count = SPECPDL_INDEX ();
-          specbind (handler_var, val);
-          return unbind_to (count, Fprogn (handler_body));
+          /* Whoever longjumped to us unwound the stack to C->pdlcount before
+             throwing, so the unbind_to will undo just this binding.  */
+          break;
         }
     }
 
-  Lisp_Object CACHEABLE result = eval_sub (bodyform);
-  handlerlist = oldhandlerlist;
-  if (!NILP (success_handler))
-    {
-      if (NILP (var))
-        return Fprogn (XCDR (success_handler));
+  if (NILP (var))
+    return Fprogn (handler_body);
 
-      Lisp_Object handler_var = var;
-      if (!NILP (Vinternal_interpreter_environment))
-        {
-          result = Fcons (Fcons (var, result),
-                       Vinternal_interpreter_environment);
-          handler_var = Qinternal_interpreter_environment;
-        }
-
-      specpdl_ref count = SPECPDL_INDEX ();
-      specbind (handler_var, result);
-      return unbind_to (count, Fprogn (XCDR (success_handler)));
+  if (!NILP (Vinternal_interpreter_environment))
+    {
+      val = Fcons (Fcons (var, val),
+                   Vinternal_interpreter_environment);
+      var = Qinternal_interpreter_environment;
     }
-  return result;
+
+  specpdl_ref count = SPECPDL_INDEX ();
+  specbind (var, val);
+  return unbind_to (count, Fprogn (handler_body));
 }
 
 /* Call the function BFUN with no arguments, catching errors within it
@@ -1740,7 +1725,7 @@ push_handler (Lisp_Object tag_ch_val, enum handlertype handlertype)
 struct handler *
 push_handler_nosignal (Lisp_Object tag_ch_val, enum handlertype handlertype)
 {
-  struct handler *CACHEABLE c = handlerlist->nextfree;
+  struct handler *c = handlerlist->nextfree;
   if (!c)
     {
       c = malloc (sizeof *c);