[Bug tree-optimization/65887] remove va_arg ap copies
vries at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Mon Apr 27 07:40:00 GMT 2015
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 (¶m, 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 (¶m, 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.
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