Re: [PATCH] Fix associate_plusminus A + ~A optimization (PR tree-optimization/48717)

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

On Fri, Apr 22, 2011 at 3:41 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> On the following testcase associate_plusminus optimizes
> A + ~A into INTEGER_CST { -1, -1 } with type unsigned short, which
> confuses enough following passes on (int) cast of that into
> assuming it is -1 instead of 65535.

Ick.

> Fixed by using build_int_cst_type, which is what e.g. fold-const.c
> uses when optimizing X + ~X.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
> and 4.6 (where the bug is just latent)? ?4.5 didn't have
> associate_plusminus.

Ok for both.

build_int_cst looks seriously broken, I think we want to make it
an alias of build_int_cst_type, or rather call that from
build_int_cst.

Thanks,
Richard.

> 2011-04-22 ?Jakub Jelinek ?<jakub@redhat.com>
>
> ? ? ? ?PR tree-optimization/48717
> ? ? ? ?* tree-ssa-forwprop.c (associate_plusminus): For A + ~A and
> ? ? ? ?~A + A optimizations use build_int_cst_type instead of build_int_cst.
>
> ? ? ? ?* gcc.c-torture/execute/pr48717.c: New test.
>
> --- gcc/tree-ssa-forwprop.c.jj ?2011-04-01 23:09:21.000000000 +0200
> +++ gcc/tree-ssa-forwprop.c ? ? 2011-04-22 11:57:10.000000000 +0200
> @@ -1815,7 +1815,7 @@ associate_plusminus (gimple stmt)
> ? ? ? ? ? ? ? ?{
> ? ? ? ? ? ? ? ? ?/* ~A + A -> -1. ?*/
> ? ? ? ? ? ? ? ? ?code = INTEGER_CST;
> - ? ? ? ? ? ? ? ? rhs1 = build_int_cst (TREE_TYPE (rhs2), -1);
> + ? ? ? ? ? ? ? ? rhs1 = build_int_cst_type (TREE_TYPE (rhs2), -1);
> ? ? ? ? ? ? ? ? ?rhs2 = NULL_TREE;
> ? ? ? ? ? ? ? ? ?gimple_assign_set_rhs_with_ops (&gsi, code, rhs1, NULL_TREE);
> ? ? ? ? ? ? ? ? ?gcc_assert (gsi_stmt (gsi) == stmt);
> @@ -1915,7 +1915,7 @@ associate_plusminus (gimple stmt)
> ? ? ? ? ? ? ? ?{
> ? ? ? ? ? ? ? ? ?/* A + ~A -> -1. ?*/
> ? ? ? ? ? ? ? ? ?code = INTEGER_CST;
> - ? ? ? ? ? ? ? ? rhs1 = build_int_cst (TREE_TYPE (rhs1), -1);
> + ? ? ? ? ? ? ? ? rhs1 = build_int_cst_type (TREE_TYPE (rhs1), -1);
> ? ? ? ? ? ? ? ? ?rhs2 = NULL_TREE;
> ? ? ? ? ? ? ? ? ?gimple_assign_set_rhs_with_ops (&gsi, code, rhs1, NULL_TREE);
> ? ? ? ? ? ? ? ? ?gcc_assert (gsi_stmt (gsi) == stmt);
> --- gcc/testsuite/gcc.c-torture/execute/pr48717.c.jj ? ?2011-04-22 11:59:23.000000000 +0200
> +++ gcc/testsuite/gcc.c-torture/execute/pr48717.c ? ? ? 2011-04-22 11:58:48.000000000 +0200
> @@ -0,0 +1,26 @@
> +/* PR tree-optimization/48717 */
> +
> +extern void abort (void);
> +
> +int v = 1, w;
> +
> +unsigned short
> +foo (unsigned short x, unsigned short y)
> +{
> + ?return x + y;
> +}
> +
> +void
> +bar (void)
> +{
> + ?v = foo (~w, w);
> +}
> +
> +int
> +main ()
> +{
> + ?bar ();
> + ?if (v != (unsigned short) -1)
> + ? ?abort ();
> + ?return 0;
> +}
>
> ? ? ? ?Jakub
>