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* [Bug tree-optimization/99966] New: Bounds check not eliminated by assert
@ 2021-04-08 1:23 jmuizelaar at mozilla dot com
2021-04-08 7:19 ` [Bug tree-optimization/99966] " rguenth at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: jmuizelaar at mozilla dot com @ 2021-04-08 1:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Bug ID: 99966
Summary: Bounds check not eliminated by assert
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jmuizelaar at mozilla dot com
Target Milestone: ---
#include <cassert>
#include <cstdint>
#include <cstddef>
#include <vector>
uint64_t f(std::vector<uint64_t>& data, size_t start, size_t end){
assert(start < end && start < data.size() && end <= data.size());
uint64_t total = 0;
for (size_t i = start; i < end; i++) {
total += data.at(i);
}
return total;
}
https://godbolt.org/z/Ksecrec11
Clang is able to eliminate the the check when using -mllvm
-enable-constraint-elimination
https://godbolt.org/z/K67b8PTM9
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/99966] Bounds check not eliminated by assert
2021-04-08 1:23 [Bug tree-optimization/99966] New: Bounds check not eliminated by assert jmuizelaar at mozilla dot com
@ 2021-04-08 7:19 ` rguenth at gcc dot gnu.org
2022-01-11 18:59 ` amacleod at redhat dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-04-08 7:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-04-08
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Blocks| |85316
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
For the testcase the issue is that the range check is inside the loop and
eliminating it requires symbolic range propagation to work "better".
We arrive at
i_28: long unsigned int [_32, +INF] EQUIVALENCES: { i_1 i_12 } (2 elements)
i_12: size_t VARYING
for
<bb 2> [local count: 118253447]:
if (start_4(D) < end_5(D))
goto <bb 3>; [99.96%]
else
goto <bb 4>; [0.04%]
<bb 3> [local count: 118206146]:
_9 = MEM[(const struct vector *)data_7(D)].D.18843._M_impl.D.18156._M_finish;
_8 = MEM[(const struct vector *)data_7(D)].D.18843._M_impl.D.18156._M_start;
_14 = _9 - _8;
_15 = _14 /[ex] 8;
_16 = (long unsigned int) _15;
_33 = _16 >= end_5(D);
_34 = _16 > start_4(D);
_22 = _33 & _34;
if (_22 != 0)
goto <bb 7>; [99.92%]
else
goto <bb 4>; [0.08%]
<bb 4> [local count: 141847]:
__assert_fail ("start < end && start < data.size() && end <= data.size()",
"t.C", 7, "uint64_t f(std::vector<long unsigned int>&, size_t, size_t)");
<bb 5> [local count: 834435851]:
if (i_12 >= _16)
goto <bb 6>; [0.05%]
else
goto <bb 7>; [99.95%]
<bb 6> [local count: 381018]:
# i_38 = PHI <i_12(5)>
std::__throw_out_of_range_fmt ("vector::_M_range_check: __n (which is %zu) >=
this->size() (which is %zu)", i_38, _16);
<bb 7> [local count: 952166435]:
# total_3 = PHI <total_11(5), 0(3)>
# i_2 = PHI <i_12(5), start_4(D)(3)>
_10 = MEM[(value_type &)_8 + i_2 * 8];
total_11 = total_3 + _10;
i_12 = i_2 + 1;
if (i_12 != end_5(D))
goto <bb 5>; [87.64%]
else
goto <bb 8>; [12.36%]
<bb 8> [local count: 117730583]:
# total_37 = PHI <total_11(7)>
return total_37;
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/99966] Bounds check not eliminated by assert
2021-04-08 1:23 [Bug tree-optimization/99966] New: Bounds check not eliminated by assert jmuizelaar at mozilla dot com
2021-04-08 7:19 ` [Bug tree-optimization/99966] " rguenth at gcc dot gnu.org
@ 2022-01-11 18:59 ` amacleod at redhat dot com
2022-11-03 19:31 ` amacleod at redhat dot com
2022-11-28 22:09 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: amacleod at redhat dot com @ 2022-01-11 18:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Andrew Macleod <amacleod at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amacleod at redhat dot com
--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
looking at VRP2:
the initial assert provides:
Relational : (start_4(D) < end_5(D))
Relational : (_16 > start_4(D))
Relational : (end_5(D) <= _16)
unfortunately, the loop back edge is:
i_12 = i_17 + 1;
if (end_5(D) != i_12)
goto <bb 5>; [89.00%]
else
goto <bb 8>; [11.00%]
so it only registers what it knows from the branch:
Relational : (i_12 != end_5(D))
so when it gets to the bounds check at:
if (i_12 >= _16)
goto <bb 6>; [0.04%]
else
goto <bb 10>; [99.96%]
It doesn't really know the answer. If the loop branch had remained
if (i_12 < end_5) instead of being changed, then we would instead get the
relation:
Relational : (i_12 < end_5(D))
which combined with the earlier Relational : (end_5(D) <= _16), should register
the transitive relation (i_12 < _16), and enable removal of the check.
This is transformed in ivopts, which runs after vrp1. A quick check shows at
VRP1 time, the bounds are still using the < format...
In fact... running with --param=vrp1-mode=ranger registers this exact
transitive relation, and produces:
Relational : (i_2 < _16)
Relational : (i_2 < end_5(D))
<bb 6> [local count: 952547451]:
if (0 != 0)
goto <bb 7>; [0.04%]
else
goto <bb 8>; [99.96%]
and eliminates the bounds check.
So we can close this PR when we turn ranger on by default for VRP1.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/99966] Bounds check not eliminated by assert
2021-04-08 1:23 [Bug tree-optimization/99966] New: Bounds check not eliminated by assert jmuizelaar at mozilla dot com
2021-04-08 7:19 ` [Bug tree-optimization/99966] " rguenth at gcc dot gnu.org
2022-01-11 18:59 ` amacleod at redhat dot com
@ 2022-11-03 19:31 ` amacleod at redhat dot com
2022-11-28 22:09 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: amacleod at redhat dot com @ 2022-11-03 19:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Andrew Macleod <amacleod at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> ---
Fixed by
commit e7310e24b1c0ca67b1bb507c1330b2bf39e59e32
Author: Andrew MacLeod <amacleod@redhat.com>
Date: Tue Oct 25 16:42:41 2022 -0400
Make ranger vrp1 default.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/99966] Bounds check not eliminated by assert
2021-04-08 1:23 [Bug tree-optimization/99966] New: Bounds check not eliminated by assert jmuizelaar at mozilla dot com
` (2 preceding siblings ...)
2022-11-03 19:31 ` amacleod at redhat dot com
@ 2022-11-28 22:09 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-11-28 22:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |13.0
Keywords| |missed-optimization
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-04-08 1:23 [Bug tree-optimization/99966] New: Bounds check not eliminated by assert jmuizelaar at mozilla dot com
2021-04-08 7:19 ` [Bug tree-optimization/99966] " rguenth at gcc dot gnu.org
2022-01-11 18:59 ` amacleod at redhat dot com
2022-11-03 19:31 ` amacleod at redhat dot com
2022-11-28 22:09 ` pinskia at gcc dot gnu.org
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