On Sat, Apr 30, 2016 at 2:28 PM, Patrick Palka <patr...@parcs.ath.cx> wrote:
> `On Fri, Apr 29, 2016 at 3:15 PM, Jeff Law <l...@redhat.com> wrote:
>> On 04/19/2016 11:50 AM, Patrick Palka wrote:
>>
>>> 1. This patch introduces a "regression" in gcc.dg/tree-ssa/ssa-thread-11.c
>>> in that we no longer perform FSM threading during vrp2 but instead we
>>> detect two new jump threading opportunities during vrp1. Not sure if
>>> the new code is better but it is shorter. I wonder how this should be
>>> resolved...
>>
>> Definitely not a regression. As you note we thread two jumps earlier
>> utilizing your new code. With the old code we're dependent upon other
>> simplifications occurring which eventually exposes the FSM threads that the
>> test is checking for in vrp2.
>>
>> I think we just want to remove the test for FSM jump threads in VRP2. We get
>> coverage for your test via ssa-thread-14. That should just leave the
>> verification that we do not have irreducible loops at the end of VRP2 in
>> ssa-thread-11. I'll make that change.
>>
>> I do see what appears to be a missed jump thread, but that's not affected
>> positively or negatively by your change. There's a reasonable chance it's
>> only exposed by normal thread jumps in VRP2 and since we don't iterate, it's
>> left in the IL. I haven't analyzed it in detail, but my hope is that when I
>> pull the backwards threading out into its own pass that we'll start picking
>> up more of these secondary effects.
>
> Interesting info. I also spotted another minor optimization
> opportunity within this test case, although more related to vrp than
> to jump threading. It would require iterating over the use statements
> of a subexpression within a conditional, and it turns out that VRP
> already does this so it's only a matter of adding another case to test
> for during each iteration. I'll post a patch when it's ready.
>
>>
>>
>>>
>>> gcc/ChangeLog:
>>>
>>> * tree-ssa-threadedge.c (simplify_control_stmt_condition): Split
>>> out into ...
>>> (simplify_control_stmt_condition_1): ... here. Recurse into
>>> BIT_AND_EXPRs and BIT_IOR_EXPRs.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> * gcc.dg/tree-ssa/ssa-thread-14.c: New test.
>>> ---
>>
>> I fixed a few formatting nits (too long lines).
>>
This one fails on Linux/x86-64 and Linux/x86. This patch fixes it. OK
for trunk?
--
H.J.
---
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-14.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-14.c
index db9ed3b..e2ac2f7 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-14.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-14.c
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-additional-options "-O2 -fdump-tree-vrp" } */
+/* { dg-additional-options "-O2 -fdump-tree-vrp-details" } */
/* { dg-final { scan-tree-dump-times "Threaded jump" 8 "vrp1" } } */
void foo (void);
