Re: [PATCH] Expand switch statements with a single (or none) non-default case.

[Martin Liška <mliska at suse dot cz>]

On 08/30/2017 02:56 PM, Richard Biener wrote:
> On Wed, Aug 30, 2017 at 2:32 PM, Martin Liška <mliska@suse.cz> wrote:
>> On 08/30/2017 02:28 PM, Richard Biener wrote:
>>> On Wed, Aug 30, 2017 at 1:13 PM, Martin Liška <mliska@suse.cz> wrote:
>>>> Hi.
>>>>
>>>> Simple transformation of switch statements where degenerated switch can be interpreted
>>>> as gimple condition (or removed if having any non-default case). I originally though
>>>> that we don't have switch statements without non-default cases, but PR82032 shows we
>>>> can see it.
>>>>
>>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>>>
>>>> Ready to be installed?
>>>
>>> While I guess this case is ok to handle here it would be nice if CFG cleanup
>>> would do the same.  I suppose find_taken_edge somehow doesn't work for
>>> this case even after my last enhancement?  Or is CFG cleanup for some reason
>>> not run?
>>
>> Do you mean both with # of non-default edges equal to 0 and 1?
>> Let me take a look.
> 
> First and foremost 0.  The case of 1 non-default and a default would
> need extra code.

For the test-case I reduced, one needs:

diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index b7593068ea9..13af516c6ac 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -8712,7 +8712,7 @@ const pass_data pass_data_split_crit_edges =
   PROP_no_crit_edges, /* properties_provided */
   0, /* properties_destroyed */
   0, /* todo_flags_start */
-  0, /* todo_flags_finish */
+  TODO_cleanup_cfg, /* todo_flags_finish */
 };
 
 class pass_split_crit_edges : public gimple_opt_pass

And the code eliminates the problematic switch statement. Do you believe it's the right approach
to add the clean up and preserve the assert in tree-switch-conversion.c?

For the case with # of edges == 1, should I place it to tree-cfg.c in order to trigger it as a clean-up?
Thoughts?

Martin

> 
> Richard.
> 
>> Martin
>>
>>>
>>> Richard.
>>>
>>>> Martin
>>>>
>>>> gcc/ChangeLog:
>>>>
>>>> 2017-08-25  Martin Liska  <mliska@suse.cz>
>>>>
>>>>         PR tree-optimization/82032
>>>>         * tree-switch-conversion.c (generate_high_low_equality): New
>>>>         function.
>>>>         (expand_degenerated_switch): Likewise.
>>>>         (process_switch): Call expand_degenerated_switch.
>>>>         (try_switch_expansion): Likewise.
>>>>         (emit_case_nodes): Use generate_high_low_equality.
>>>>
>>>> gcc/testsuite/ChangeLog:
>>>>
>>>> 2017-08-25  Martin Liska  <mliska@suse.cz>
>>>>
>>>>         PR tree-optimization/82032
>>>>         * gcc.dg/tree-ssa/pr68198.c: Update jump threading expectations.
>>>>         * gcc.dg/tree-ssa/switch-expansion.c: New test.
>>>>         * gcc.dg/tree-ssa/vrp34.c: Update scanned pattern.
>>>>         * g++.dg/other/pr82032.C: New test.
>>>> ---
>>>>  gcc/testsuite/g++.dg/other/pr82032.C             |  36 +++++++
>>>>  gcc/testsuite/gcc.dg/tree-ssa/pr68198.c          |   6 +-
>>>>  gcc/testsuite/gcc.dg/tree-ssa/switch-expansion.c |  14 +++
>>>>  gcc/testsuite/gcc.dg/tree-ssa/vrp34.c            |   5 +-
>>>>  gcc/tree-switch-conversion.c                     | 123 ++++++++++++++++++-----
>>>>  5 files changed, 152 insertions(+), 32 deletions(-)
>>>>  create mode 100644 gcc/testsuite/g++.dg/other/pr82032.C
>>>>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/switch-expansion.c
>>>>
>>>>
>>