* [Bug tree-optimization/96881] [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519
2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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2020-09-02 7:39 ` rguenth at gcc dot gnu.org
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From: jakub at gcc dot gnu.org @ 2020-09-01 10:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This PR should cover the CDDCE part of PR96722, e.g. as mentioned in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96722#c6
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
2020-09-01 10:55 ` [Bug tree-optimization/96881] " jakub at gcc dot gnu.org
@ 2020-09-02 7:39 ` rguenth at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2020-09-02 7:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2020-09-02
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
Target Milestone|--- |8.5
Status|UNCONFIRMED |ASSIGNED
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Mine eventually.
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2020-09-01 10:55 ` [Bug tree-optimization/96881] " jakub at gcc dot gnu.org
2020-09-02 7:39 ` rguenth at gcc dot gnu.org
@ 2020-09-17 17:58 ` jakub at gcc dot gnu.org
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From: jakub at gcc dot gnu.org @ 2020-09-17 17:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Bug 96881 depends on bug 96722, which changed state.
Bug 96722 Summary: [8/9 Regression] Clobbers on NULL since r8-1519
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96722
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
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From: rguenth at gcc dot gnu.org @ 2020-10-12 12:26 UTC (permalink / raw)
To: gcc-bugs
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Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
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From: jakub at gcc dot gnu.org @ 2021-05-14 9:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|8.5 |9.4
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.
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From: rguenth at gcc dot gnu.org @ 2021-06-01 8:18 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.4 |9.5
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2022-02-15 12:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
The CD-DCE issue is that we do not mark CLOBBERs as necessary but in the end
choose to keep them, even if we elided its control dependences. The following
fixes that in the simplest conservative way.
This is really wrong-code. Testcase
struct S { int s; ~S () {} } s;
void __attribute__((noinline))
foo (int flag)
{
s.s = 1;
if (!flag) // dependend on which path CDDCE preserves the CLOBBER gets elided
anyway
return;
s.~S();
}
int
main ()
{
foo (0);
if (s.s != 1)
__builtin_abort ();
}
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index f1034878eaf..c78d7c6ccc7 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -1272,7 +1272,7 @@ maybe_optimize_arith_overflow (gimple_stmt_iterator *gsi,
contributes nothing to the program, and can be deleted. */
static bool
-eliminate_unnecessary_stmts (void)
+eliminate_unnecessary_stmts (bool aggressive)
{
bool something_changed = false;
basic_block bb;
@@ -1366,7 +1366,9 @@ eliminate_unnecessary_stmts (void)
break;
}
}
- if (!dead)
+ if (!dead
+ && (!aggressive
+ || bitmap_bit_p (visited_control_parents,
bb->index)))
{
bitmap_clear (debug_seen);
continue;
@@ -1876,7 +1878,7 @@ perform_tree_ssa_dce (bool aggressive)
propagate_necessity (aggressive);
BITMAP_FREE (visited);
- something_changed |= eliminate_unnecessary_stmts ();
+ something_changed |= eliminate_unnecessary_stmts (aggressive);
something_changed |= cfg_altered;
/* We do not update postdominators, so free them unconditionally. */
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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From: cvs-commit at gcc dot gnu.org @ 2022-02-18 7:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:422d1d378e52418d821781ad756cf3eafc3fa9a2
commit r12-7292-g422d1d378e52418d821781ad756cf3eafc3fa9a2
Author: Richard Biener <rguenther@suse.de>
Date: Tue Feb 15 13:32:22 2022 +0100
tree-optimization/96881 - CD-DCE and CLOBBERs
CD-DCE does not consider CLOBBERs as necessary in the attempt
to not prevent DCE of SSA defs it uses. A side-effect of that
is that it also removes all its control dependences if they are
not made necessary by other means. When we later try to preserve
as many CLOBBERs as possible we have to make sure we also
preserved the controlling conditions, otherwise a CLOBBER can
now appear on a path where it was not executed before, leading
to wrong code as seen in the testcase.
I've tried to continue to handle both direct and indirect
CLOBBERs optimistically, allowing CD-DCE to remove control
flow that just controls CLOBBERs but that regresses for
example the stack coalescing test g++.dg/opt/pr80032.C.
The pattern there is
if (pred) D.2512 = CLOBBER; else D.2512 = CLOBBER;
basically we have all paths leading to the same clobber but
we could safely cut some branches which we do not realize
early enough. This regression can be mitigated by no longer
considering direct CLOBBERs optimistically - the original
motivation for the CD-DCE handling wasn't removal of control
flow but SSA defs of the address.
Handling indirect vs. direct clobbers differently feels
somewhat wrong, still the patch goes with this solution.
2022-02-15 Richard Biener <rguenther@suse.de>
PR tree-optimization/96881
* tree-ssa-dce.cc (mark_stmt_if_obviously_necessary): Comment
CLOBBER handling.
(control_parents_preserved_p): New function.
(eliminate_unnecessary_stmts): Check that we preserved control
parents before retaining a CLOBBER.
(perform_tree_ssa_dce): Pass down aggressive flag
to eliminate_unnecessary_stmts.
* g++.dg/torture/pr96881-1.C: New testcase.
* g++.dg/torture/pr96881-2.C: Likewise.
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2022-05-27 9:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|9.5 |10.4
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9 branch is being closed
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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From: jakub at gcc dot gnu.org @ 2022-06-28 10:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |10.5
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.
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2020-09-01 10:54 [Bug tree-optimization/96881] New: [8/9/10/11 Regression] Clobbers on NULL vs. DCE since r8-1519 jakub at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2023-07-07 10:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96881
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.5 |11.5
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.
^ permalink raw reply [flat|nested] 12+ messages in thread