Fix gimplify_expr ICE with Labels as Values (PR middle-end/79537)
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Message ID CAFiYyc0JiSofWaj-8cX_svVSXzkYhFWdnPUK-d4+j855rtXOGA@mail.gmail.com
State New
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Commit Message

Richard Biener Feb. 20, 2017, 9:51 a.m. UTC
On Fri, Feb 17, 2017 at 2:53 PM, Marek Polacek <polacek@redhat.com> wrote:
> We are crashing with a label as a value without accompanying goto.
> The problem is that TREE_SIDE_EFFECTS and FORCED_LABEL use the same
> ->base.side_effects_flag, so gimplify_expr is confused.  We don't
> ICE with 'goto *&&L;' becase then we take this path:
> 11406         case GOTO_EXPR:
> 11407           /* If the target is not LABEL, then it is a computed jump
> 11408              and the target needs to be gimplified.  */
> 11409           if (TREE_CODE (GOTO_DESTINATION (*expr_p)) != LABEL_DECL)
> 11410             {
> 11411               ret = gimplify_expr (&GOTO_DESTINATION (*expr_p), pre_p,
> 11412                                    NULL, is_gimple_val, fb_rvalue);
> and because of that fb_rvalue we won't go to the switch where the ICE
> occured.  Because '*&&L;' on its own is useless, I think we can simply
> discard it, which is what the following does.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk and 6?

I think I prefer


(with a comment).  Ideally we'd have TREE_NOT_CHECK (NON_TYPE_CHEC
(NODE), LABEL_DECL) on
TREE_SIDE_EFFECTS but that may have unwanted fallout at this point.

Ok with the above change.

Thanks,
RIchard.

> 2017-02-17  Marek Polacek  <polacek@redhat.com>
>
>         PR middle-end/79537
>         * gimplify.c (gimplify_expr): Handle unused *&&L;.
>
>         * gcc.dg/comp-goto-4.c: New.
>
> diff --git gcc/gimplify.c gcc/gimplify.c
> index 1b9c8d2..5524357 100644
> --- gcc/gimplify.c
> +++ gcc/gimplify.c
> @@ -12003,6 +12003,11 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
>                              gimple_test_f, fallback);
>               break;
>
> +           case LABEL_DECL:
> +             /* We can get here with code such as "*&&L;", where L is
> +                a LABEL_DECL that is marked as FORCED_LABEL.  Skip it.  */
> +             break;
> +
>             default:
>                /* Anything else with side-effects must be converted to
>                   a valid statement before we get here.  */
> diff --git gcc/testsuite/gcc.dg/comp-goto-4.c gcc/testsuite/gcc.dg/comp-goto-4.c
> index e69de29..51a6a86 100644
> --- gcc/testsuite/gcc.dg/comp-goto-4.c
> +++ gcc/testsuite/gcc.dg/comp-goto-4.c
> @@ -0,0 +1,21 @@
> +/* PR middle-end/79537 */
> +/* { dg-do compile } */
> +/* { dg-options "" } */
> +/* { dg-require-effective-target indirect_jumps } */
> +/* { dg-require-effective-target label_values } */
> +
> +void
> +f (void)
> +{
> +L:
> +  *&&L;
> +}
> +
> +void
> +f2 (void)
> +{
> +   void *p;
> +L:
> +   p = &&L;
> +   *p; /* { dg-warning "dereferencing 'void \\*' pointer" } */
> +}
>
>         Marek

Patch
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Index: gcc/gimplify.c
===================================================================
--- gcc/gimplify.c      (revision 245594)
+++ gcc/gimplify.c      (working copy)
@@ -11977,7 +11977,8 @@  gimplify_expr (tree *expr_p, gimple_seq
     {
       /* We aren't looking for a value, and we don't have a valid
         statement.  If it doesn't have side-effects, throw it away.  */
-      if (!TREE_SIDE_EFFECTS (*expr_p))
+      if (TREE_CODE (*expr_p) == LABEL_DECL
+          || !TREE_SIDE_EFFECTS (*expr_p))
        *expr_p = NULL;
       else if (!TREE_THIS_VOLATILE (*expr_p))
        {