From: Richard Biener <richard.guenther@gmail.com>
To: Jeff Law <law@redhat.com>
Cc: Aldy Hernandez <aldyh@redhat.com>,
gcc-patches <gcc-patches@gcc.gnu.org>,
Jan Hubicka <hubicka@ucw.cz>
Subject: Re: [patch/committed] PR middle-end/65233 make walk-ssa_copies handle empty PHIs
Date: Wed, 04 Mar 2015 13:30:00 -0000 [thread overview]
Message-ID: <CAFiYyc0k5pkR8ju+VM1G6FNvg2xkjRwPEu6XtZuqy-uENc3GYQ@mail.gmail.com> (raw)
In-Reply-To: <CAFiYyc0FWK45geB3qKoj-RjQM3mPh3+d3o_Kuh+KZsBrzBUskQ@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 3268 bytes --]
On Wed, Mar 4, 2015 at 1:41 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Mar 4, 2015 at 6:27 AM, Jeff Law <law@redhat.com> wrote:
>> On 03/02/15 01:38, Richard Biener wrote:
>>>
>>> On Mon, Mar 2, 2015 at 6:34 AM, Aldy Hernandez <aldyh@redhat.com> wrote:
>>>>
>>>> As I mention in the PR...
>>>>
>>>> What's happening here is that the ipa_polymorphic_call_context
>>>> constructor
>>>> is calling walk_ssa_copies on a PHI node that has no arguments. This
>>>> happens because finalize_jump_threads eventually removes some PHI
>>>> arguments
>>>> as it's redirecting some edges, leaving a PHI with no arguments:
>>>>
>>>> SR.33_23 = PHI <>
>>>>
>>>> This should get cleaned up later, but the IPA polymorphic code gets
>>>> called
>>>> during the actual CFG clean-up, and walk_ssa_copies cannot handle an
>>>> empty
>>>> PHI.
>>>>
>>>> Approved by Honza.
>>>>
>>>> Fully tested on x86-64 Linux and verified that the patch fixes the ICE on
>>>> an
>>>> x86-64 Linux cross aarch64-linux-gnu cc1plus.
>>>>
>>>> Committed to mainline.
>>>
>>>
>>> I think the real issue is that the walking code is executed via fold_stmt
>>> when
>>> called with an API that tells you not to walk SSA use-def chains.
>>
>> ? We have something that tells us not to walk the chains? I don't see it
>> in an API for fold_stmt. How is the ipa-polymorphic code supposed to know
>> when it can't follow the chains?
>
> It gets passed the valueize callback now which returns NULL_TREE for
> SSA names we can't follow.
Btw, for match-and-simplify I had to use that as default for fold_stmt
_exactly_ because of the call to fold_stmt from replace_uses_by
via merge-blocks from cfgcleanup. This is because replace-uses-by
doesn't have all uses replaced before it folds the stmt!
We also have the "weaker" in-place flag.
>> The restrictions on what we can do while we're in the inconsistent state
>> prior to updating the ssa graph aren't defined anywhere and I doubt anyone
>> really knows what they are. That's obviously concerning.
>>
>> We might consider trying to narrow the window in which these inconsistencies
>> are allowed. To do that I think we need to split cfgcleanup into two
>> distinct parts. First is unreachable block removal (which is needed so that
>> we can compute the dominators). Second is everything else.
>>
>> The order of operations would be something like
>>
>> remove unreachable blocks
>> ssa graph update
>> rest of cfg_cleanup
>>
>> That just feels too intrusive to try at this stage though.
>
> Well, not folding statements from cfg-cleanup would be better.
>
> I'll have a look at the testcase in the PR and will come back with a
> suggestion on what to do for GCC 5.
I'd say that the devirtualization code is quite a heavy thing do to from
fold_stmt. Yes - it want's to catch all cases if a stmt is modified
(after which passes should fold it).
So I am testing the following on x86_64 (verified it fixes the testcase
with a aarch64 cross).
Richard.
2015-03-04 Richard Biener <rguenther@suse.de>
PR middle-end/65233
* ipa-polymorphic-call.c: Include tree-ssa-operands.h and
tree-into-ssa.h.
(walk_ssa_copies): Revert last chage. Instead do not walk
SSA names registered for SSA update.
[-- Attachment #2: fix-pr65233 --]
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2015-03-04 Richard Biener <rguenther@suse.de>
PR middle-end/65233
* ipa-polymorphic-call.c: Include tree-ssa-operands.h and
tree-into-ssa.h.
(walk_ssa_copies): Revert last chage. Instead do not walk
SSA names registered for SSA update.
Index: gcc/ipa-polymorphic-call.c
===================================================================
--- gcc/ipa-polymorphic-call.c (revision 221149)
+++ gcc/ipa-polymorphic-call.c (working copy)
@@ -81,6 +81,8 @@ along with GCC; see the file COPYING3.
#include "data-streamer.h"
#include "lto-streamer.h"
#include "streamer-hooks.h"
+#include "tree-ssa-operands.h"
+#include "tree-into-ssa.h"
/* Return true when TYPE contains an polymorphic type and thus is interesting
for devirtualization machinery. */
@@ -804,7 +806,9 @@ walk_ssa_copies (tree op, hash_set<tree>
STRIP_NOPS (op);
while (TREE_CODE (op) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (op)
- && SSA_NAME_DEF_STMT (op)
+ /* We might be called via fold_stmt during cfgcleanup where
+ SSA form need not be up-to-date. */
+ && !name_registered_for_update_p (op)
&& (gimple_assign_single_p (SSA_NAME_DEF_STMT (op))
|| gimple_code (SSA_NAME_DEF_STMT (op)) == GIMPLE_PHI))
{
@@ -835,10 +839,7 @@ walk_ssa_copies (tree op, hash_set<tree>
{
gimple phi = SSA_NAME_DEF_STMT (op);
- if (gimple_phi_num_args (phi) > 2
- /* We can be called while cleaning up the CFG and can
- have empty PHIs about to be removed. */
- || gimple_phi_num_args (phi) == 0)
+ if (gimple_phi_num_args (phi) > 2)
goto done;
if (gimple_phi_num_args (phi) == 1)
op = gimple_phi_arg_def (phi, 0);
next prev parent reply other threads:[~2015-03-04 13:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-02 5:34 Aldy Hernandez
2015-03-02 8:38 ` Richard Biener
2015-03-03 20:18 ` Jan Hubicka
2015-03-04 5:27 ` Jeff Law
2015-03-04 12:41 ` Richard Biener
2015-03-04 13:30 ` Richard Biener [this message]
2015-03-04 21:22 ` Jan Hubicka
2015-03-05 0:54 ` Jan Hubicka
2015-03-05 8:47 ` Richard Biener
2015-03-05 16:10 ` Jeff Law
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