From: Richard Biener <richard.guenther@gmail.com>
To: Alexandre Oliva <aoliva@redhat.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PR68083] stop ifcombine from moving uninitialized uses before their guards
Date: Mon, 02 Nov 2015 09:32:00 -0000 [thread overview]
Message-ID: <CAFiYyc1G5peumVDBxRonSOQwAOc9gA9j=U9dCg+gDm2_LPSifA@mail.gmail.com> (raw)
In-Reply-To: <or8u6kfp8l.fsf@livre.home>
On Fri, Oct 30, 2015 at 2:41 PM, Alexandre Oliva <aoliva@redhat.com> wrote:
> The ifcombine pass may move a conditional access to an uninitialized
> value before the condition that ensures it is always well-defined,
> thus introducing undefined behavior. Stop it from doing so.
>
> Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to install?
Ok.
Thanks,
Richard.
>
> Incidentally, bb_no_side_effects_p (inner_cond_bb) is called in all four
> tests in tree_ssa_ifcombine_bb_1, for each outer_cond_bb that
> tree_ssa_ifcombine_bb might choose. Is there any reason to not factor
> it out to the test that checks whether the inner_cond_bb is indeed an
> if_then_else block, early in tree_ssa_ifcombine_bb, so as to
> short-circuit the whole thing when the inner block is not viable?
>
>
> for gcc/ChangeLog
>
> PR tree-optimization/68083
> * tree-ssa-ifcombine.c: Include tree-ssa.h.
> (bb_no_side_effects_p): Test for undefined uses too.
> * tree-ssa.c (gimple_uses_undefined_value_p): New.
> * tree-ssa.h (gimple_uses_undefined_value_p): Declare.
>
> for gcc/testsuite/ChangeLog
>
> PR tree-optimization/68083
> * gcc.dg/torture/pr68083.c: New. From Zhendong Su.
> ---
> gcc/testsuite/gcc.dg/torture/pr68083.c | 35 ++++++++++++++++++++++++++++++++
> gcc/tree-ssa-ifcombine.c | 2 ++
> gcc/tree-ssa.c | 18 ++++++++++++++++
> gcc/tree-ssa.h | 1 +
> 4 files changed, 56 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr68083.c
>
> diff --git a/gcc/testsuite/gcc.dg/torture/pr68083.c b/gcc/testsuite/gcc.dg/torture/pr68083.c
> new file mode 100644
> index 0000000..ae24781
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr68083.c
> @@ -0,0 +1,35 @@
> +/* { dg-do run } */
> +
> +int a = 2, b = 1, c = 1;
> +
> +int
> +fn1 ()
> +{
> + int d;
> + for (; a; a--)
> + {
> + for (d = 0; d < 4; d++)
> + {
> + int k;
> + if (c < 1)
> + if (k)
> + c = 0;
> + if (b)
> + continue;
> + return 0;
> + }
> + b = !1;
> + }
> + return 0;
> +}
> +
> +int
> +main ()
> +{
> + fn1 ();
> +
> + if (a != 1)
> + __builtin_abort ();
> +
> + return 0;
> +}
> diff --git a/gcc/tree-ssa-ifcombine.c b/gcc/tree-ssa-ifcombine.c
> index ca55b57..622dc6b 100644
> --- a/gcc/tree-ssa-ifcombine.c
> +++ b/gcc/tree-ssa-ifcombine.c
> @@ -41,6 +41,7 @@ along with GCC; see the file COPYING3. If not see
> #include "gimple-iterator.h"
> #include "gimplify-me.h"
> #include "tree-cfg.h"
> +#include "tree-ssa.h"
>
> #ifndef LOGICAL_OP_NON_SHORT_CIRCUIT
> #define LOGICAL_OP_NON_SHORT_CIRCUIT \
> @@ -125,6 +126,7 @@ bb_no_side_effects_p (basic_block bb)
> continue;
>
> if (gimple_has_side_effects (stmt)
> + || gimple_uses_undefined_value_p (stmt)
> || gimple_could_trap_p (stmt)
> || gimple_vuse (stmt))
> return false;
> diff --git a/gcc/tree-ssa.c b/gcc/tree-ssa.c
> index c7be442..8dc2d61 100644
> --- a/gcc/tree-ssa.c
> +++ b/gcc/tree-ssa.c
> @@ -1210,6 +1210,24 @@ ssa_undefined_value_p (tree t, bool partial)
> }
>
>
> +/* Return TRUE iff STMT, a gimple statement, references an undefined
> + SSA name. */
> +
> +bool
> +gimple_uses_undefined_value_p (gimple *stmt)
> +{
> + ssa_op_iter iter;
> + tree op;
> +
> + FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_USE)
> + if (ssa_undefined_value_p (op))
> + return true;
> +
> + return false;
> +}
> +
> +
> +
> /* If necessary, rewrite the base of the reference tree *TP from
> a MEM_REF to a plain or converted symbol. */
>
> diff --git a/gcc/tree-ssa.h b/gcc/tree-ssa.h
> index 5a409e5..3b5bd70 100644
> --- a/gcc/tree-ssa.h
> +++ b/gcc/tree-ssa.h
> @@ -51,6 +51,7 @@ extern bool tree_ssa_useless_type_conversion (tree);
> extern tree tree_ssa_strip_useless_type_conversions (tree);
>
> extern bool ssa_undefined_value_p (tree, bool = true);
> +extern bool gimple_uses_undefined_value_p (gimple *);
> extern void execute_update_addresses_taken (void);
>
> /* Given an edge_var_map V, return the PHI arg definition. */
>
>
> --
> Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
> You must be the change you wish to see in the world. -- Gandhi
> Be Free! -- http://FSFLA.org/ FSF Latin America board member
> Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
prev parent reply other threads:[~2015-11-02 9:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-30 13:57 Alexandre Oliva
2015-10-30 18:03 ` Alexandre Oliva
2015-11-02 9:32 ` Richard Biener
2015-11-02 9:32 ` Richard Biener [this message]
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