Re: [PATCH] [RFA] [PR tree-optmization/69740] Schedule loop fixups when needed

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Feb 27, 2016 at 3:59 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Feb 25, 2016 at 11:50 PM, Jeff Law <law@redhat.com> wrote:
>> On 02/25/2016 03:00 AM, Richard Biener wrote:
>>>
>>>
>>> So I fail to see how only successor edges are relevant.  Isn't the
>>> important
>>> case to catch whether we remove an edge marked EDGE_IRREDUCIBLE_LOOP?
>>> Even if the BB persists we might have exposed a new loop here.
>>>
>>> Note that it is not safe to look at {BB,EDGE}_IRREDUCIBLE_LOOP if the loop
>>> state does not have LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS set
>>> (the flags may be stale or missing).  So it might be that we can't rely on
>>> non-loop passes modifying the CFG to handle this optimistically.
>>>
>>> Thus, how about (my main point) moving this to remove_edge instead, like
>>
>> Yea.  That works.  The !loops_state_satisfies_p check will almost certainly
>> cause us to trigger loop cleanups more often, but I think it's the
>> right/safe thing to do to catch cases where we haven't go the
>> IRREDUCIBLE_LOOP flags set.
>>
>>
>> Bootstrapped and regression tested on x86_64-linux-gnu.  OK for the trunk?
>>
>> Thanks,
>> Jeff
>>
>>
>>         PR tree-optimization/69740
>>         * cfghooks.c (remove_edge): Request loop fixups if we delete
>>         an edge that might turn an irreducible loop into a natural
>>         loop.
>>
>>         PR tree-optimization/69740
>>         * gcc.c-torture/compile/pr69740-1.c: New test.
>>         * gcc.c-torture/compile/pr69740-2.c: New test.
>>
>
> This caused:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69996
>
> and may be other build failures in SPEC CPU 2006.
>

I checked this patch into trunk and will backport it to GCC 5 branch.
This test doesn't fail and all SPEC CPU 2000/2006 benchmarks pass
on GCC 5 branch with the fix for PR 69740 applied.  Is it possible that
the fix for PR 69740 exposed a latent bug on trunk?


-- 
H.J.
---
Index: ChangeLog
===================================================================
--- ChangeLog (revision 233791)
+++ ChangeLog (working copy)
@@ -1,3 +1,8 @@
+2016-02-28  H.J. Lu  <hongjiu.lu@intel.com>
+
+ PR tree-optimization/69989
+ * gcc.dg/torture/pr69989.c: New test.
+
 2016-02-28  Eric Botcazou  <ebotcazou@adacore.com>

  * gcc.target/i386/stack-realign-win.c: New test.
Index: gcc.dg/torture/pr69989.c
===================================================================
--- gcc.dg/torture/pr69989.c (nonexistent)
+++ gcc.dg/torture/pr69989.c (working copy)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+
+extern int a, b, d;
+extern char c[];
+void
+fn1 (void)
+{
+  for (;;)
+    {
+      if (b)
+ {
+LABEL_T5T5T:
+  for (; d < a; d++)
+    c[d] = 6;
+ }
+      break;
+    }
+  if (a > 6)
+    {
+      a = 4;
+      goto LABEL_T5T5T;
+    }
+}