Re: [PATCH] Avoid infinite recursion in fold_ternary/fold_cond_expr_with_comparison (PR middle-end/40692)

[Richard Guenther <richard dot guenther at gmail dot com>]

On Thu, Jul 9, 2009 at 8:49 AM, Jakub Jelinek<jakub@redhat.com> wrote:
> Hi!
>
> The recent r149060 checkin where build3 sets TREE_READONLY on COND_EXPRs
> with all arguments read-only or CONSTANT_CLASS_P causes ICE when building
> Linux kernel. ?The problem is that the C FE doesn't fully fold stuff and
> build_conditional_expr when called with those now newly TREE_READONLY
> COND_EXPRs will use a TREE_READONLY result_type, rather than the previous
> non-readonly:
> ?/* Merge const and volatile flags of the incoming types. ?*/
> ?result_type
> ? ?= build_type_variant (result_type,
> ? ? ? ? ? ? ? ? ? ? ? ? ?TREE_READONLY (op1) || TREE_READONLY (op2),
> ? ? ? ? ? ? ? ? ? ? ? ? ?TREE_THIS_VOLATILE (op1) || TREE_THIS_VOLATILE
> ? ? ? ? ? ? ? ? ? ? ? ? ?(op2));
> This means fold_ternary (COND_EXPR, <long int readonly>, <eq 0 0>, 0, 2)
> is called and fold_cond_expr_with_comparison it calls isn't prepared for
> both operands of the comparison being integers, so it replaces
> arg1 (0) with arg01 (0) and attempts to fold it again.
>
> The following patch fixes it by not replacing an integer with an integer.
> Ok for trunk if bootstrap/regtest passes?

Ok.

Thanks,
Richard.

> 2009-07-09 ?Jakub Jelinek ?<jakub@redhat.com>
>
> ? ? ? ?PR middle-end/40692
> ? ? ? ?* fold-const.c (fold_cond_expr_with_comparison): Don't replace
> ? ? ? ?arg1 with arg01 if arg1 is already INTEGER_CST.
>
> ? ? ? ?* gcc.c-torture/compile/pr40692.c: New test.
>
> --- gcc/fold-const.c.jj 2009-07-07 12:39:07.000000000 +0200
> +++ gcc/fold-const.c ? ?2009-07-09 08:10:38.000000000 +0200
> @@ -5303,6 +5303,8 @@ fold_cond_expr_with_comparison (tree typ
> ? ? switch (comp_code)
> ? ? ? {
> ? ? ? case EQ_EXPR:
> + ? ? ? if (TREE_CODE (arg1) == INTEGER_CST)
> + ? ? ? ? break;
> ? ? ? ?/* We can replace A with C1 in this case. ?*/
> ? ? ? ?arg1 = fold_convert (type, arg01);
> ? ? ? ?return fold_build3 (COND_EXPR, type, arg0, arg1, arg2);
> --- gcc/testsuite/gcc.c-torture/compile/pr40692.c.jj ? ?2009-07-09 08:19:31.000000000 +0200
> +++ gcc/testsuite/gcc.c-torture/compile/pr40692.c ? ? ? 2009-07-09 08:18:42.000000000 +0200
> @@ -0,0 +1,15 @@
> +/* PR middle-end/40692 */
> +
> +#define M1(x) (((x) & 0x00000002) ? 0x2 : ((x) & 0x1))
> +#define M2(x) (((x) & 0x0000000c) ? M1 ((x) >> 2) << 2 : M1 (x))
> +#define M3(x) (((x) & 0x000000f0) ? M2 ((x) >> 4) << 4 : M2 (x))
> +#define M4(x) (((x) & 0x0000ff00) ? M3 ((x) >> 8) << 8 : M3 (x))
> +#define M5(x) (((x) & 0xffff0000) ? M4 ((x) >> 16) << 16 : M4 (x))
> +
> +struct A { char e; char f; };
> +
> +long
> +foo (void)
> +{
> + ?return M5 (4096UL - (long) &((struct A *) 0)->f);
> +}
>
> ? ? ? ?Jakub
>