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* [Bug tree-optimization/100503] New: A possible divide by zero problem in function do_rpo_vn
@ 2021-05-10 13:59 yguoaz at cse dot ust.hk
2021-05-10 14:15 ` [Bug tree-optimization/100503] " marxin at gcc dot gnu.org
2021-05-10 16:25 ` pinskia at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: yguoaz at cse dot ust.hk @ 2021-05-10 13:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100503
Bug ID: 100503
Summary: A possible divide by zero problem in function
do_rpo_vn
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: yguoaz at cse dot ust.hk
Target Milestone: ---
In gcc/tree-ssa-sccvn.c, the function do_rpo_vn has the following code (link to
the code location:
https://github.com/gcc-mirror/gcc/blob/releases/gcc-11/gcc/tree-ssa-sccvn.c#L7815-#L7842)
static unsigned
do_rpo_vn (function *fn, edge entry, bitmap exit_bbs,
bool iterate, bool eliminate) {
...
int nex = 0;
...
for (int i = 0; i < n; ++i) {
basic_block bb = BASIC_BLOCK_FOR_FN (fn, rpo[i]);
if (bb->flags & BB_EXECUTABLE)
nex++;
}
...
statistics_histogram_event (cfun, "RPO iterations", 10*nblk / nex);
}
In the loop, the code counts the number of basic blocks with BB_EXECUTABLE flag
in variable nex and use it as divisor after exiting the loop. If no basic block
has such flag, then we will have a divide by zero problem. Is this possible ?
Or we must have at least one bb with the flag BB_EXECUTABLE ?
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/100503] A possible divide by zero problem in function do_rpo_vn
2021-05-10 13:59 [Bug tree-optimization/100503] New: A possible divide by zero problem in function do_rpo_vn yguoaz at cse dot ust.hk
@ 2021-05-10 14:15 ` marxin at gcc dot gnu.org
2021-05-10 16:25 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: marxin at gcc dot gnu.org @ 2021-05-10 14:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100503
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
CC| |rguenth at gcc dot gnu.org
Last reconfirmed| |2021-05-10
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/100503] A possible divide by zero problem in function do_rpo_vn
2021-05-10 13:59 [Bug tree-optimization/100503] New: A possible divide by zero problem in function do_rpo_vn yguoaz at cse dot ust.hk
2021-05-10 14:15 ` [Bug tree-optimization/100503] " marxin at gcc dot gnu.org
@ 2021-05-10 16:25 ` pinskia at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-05-10 16:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100503
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|NEW |RESOLVED
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There will always be at least one BB which has its BB_EXECUTABLE set.
As shown by (on line 7610):
entry->dest->flags |= BB_EXECUTABLE;
It is hard to do this kind of static anlysis without understanding the code
fully.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-05-10 16:25 UTC | newest]
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2021-05-10 13:59 [Bug tree-optimization/100503] New: A possible divide by zero problem in function do_rpo_vn yguoaz at cse dot ust.hk
2021-05-10 14:15 ` [Bug tree-optimization/100503] " marxin at gcc dot gnu.org
2021-05-10 16:25 ` pinskia at gcc dot gnu.org
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