[Bug tree-optimization/65887] remove va_arg ap copies

["vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65887

--- Comment #2 from vries at gcc dot gnu.org ---
I.
After removing the copyback using attached patch, and marking the va_arg first
argument as addressable as suggested here (
https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01314.html ) using this patch (nr
1):
...
@@ -9408,6 +9458,23 @@ gimplify_va_arg_expr (tree *expr_p, gimple_seq *pre_p,
     }

   /* Transform a VA_ARG_EXPR into an VA_ARG internal function.  */
+  mark_addressable (valist);
   ap = build_fold_addr_expr_loc (loc, valist);
   tag = build_int_cst (build_pointer_type (type), 0);
   *expr_p = build_call_expr_internal_loc (loc, IFN_VA_ARG, type, 2, ap, tag);
... 

we get the desired:
...
       e = VA_ARG (&argp, 0B);
       e = VA_ARG (&argp, 0B);
...


II.
However, we subsequently run into a verify_gimple_call failure in
gcc.c-torture/execute/va-arg-10.c, for the second argument of this va_copy:
...
            __builtin_va_copy (&apc, ap);
            ...
            D.2056 = VA_ARG (&ap, 0B);
...

Presumably because ap is not marked as addressable when gimplifying the
va_copy, but ap is later marked as addressable when gimplifying VA_ARG_EXPR.

With this patch (nr 2), we mark the second va_copy argument as addressable when
gimplifying va_copy:
...
@@ -2339,6 +2340,55 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p,
bool want_value)
       && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
     switch (DECL_FUNCTION_CODE (fndecl))
       {
+      case BUILT_IN_VA_COPY:
+       mark_addressable (CALL_EXPR_ARG (*expr_p, 1));
+       break;
       case BUILT_IN_VA_START:
         {
          builtin_va_start_p = TRUE;
...

That indeed prevents the verify_gimple_call error. But the code now contains a
copy:
...
            ap.0 = ap;
            __builtin_va_copy (&apc, ap.0);
            ...
            D.2057 = VA_ARG (&ap, 0B);
...
The copy in itself does not look incorrect, but we'd rather not have it.


III.
Furthermore, patch nr 1 triggers a verify_gimple_call error on
gcc.c-torture/execute/va-arg-14.c for the first argument of a va_copy:
...
            __builtin_va_copy (param, &local);
            ...
            D.1845 = VA_ARG (&param, 0B);
...

Using this patch (nr 3), we also mark the first argument of the copy as
addressable:
...
@@ -2341,6 +2341,7 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, bool
want_value)
       {
       case BUILT_IN_VA_COPY:
        mark_addressable (CALL_EXPR_ARG (*expr_p, 1));
+       mark_addressable (CALL_EXPR_ARG (*expr_p, 0));
        break;
       case BUILT_IN_VA_START:
         {
...

That indeed prevents the verify_gimple_call failure. But it results in this
code:
...
        param.0 = param; 
        __builtin_va_copy (param.0, &local);
        ...
        D.1846 = VA_ARG (&param, 0B);
...
which doesn't look correct: param is unmodified by the va_copy.

OTOH, the obvious tests (execute.exp=va-arg*.c, execute.exp=stdarg*.c,
callabi.exp) are passing, probably because va_list is a pointer type, and
va_copy modifies what param points to.