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* [Bug tree-optimization/23471] New: a*a (for signed ints with -fno-wrapv) is always postive
@ 2005-08-19 1:03 pinskia at gcc dot gnu dot org
2005-08-31 16:18 ` [Bug tree-optimization/23471] " pinskia at gcc dot gnu dot org
0 siblings, 1 reply; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-08-19 1:03 UTC (permalink / raw)
To: gcc-bugs
Hmm, this is both a VRP bug and a folding bug. Even though a is VARYING, we know the that a*a will
always be postive (this with -fno-wrapv which is default for C, C++ and fortran).
void link_error(void);
void f(int a)
{
int b = a;
b*=a;
if (b < 0)
link_error();
}
---
There should be no references to link_error().
There is another way of fixing this via the fold:
void link_error(void);
void f(int a)
{
if (a*a < 0)
link_error();
}
But that will miss:
void link_error(void);
void f(int a)
{
if (a*a*a*a*a*a < 0)
link_error();
}
---
Yes that is most likely to overflow but that is the whole point of -fno-wrapv.
Also ICC does not do this optimization at all.
--
Summary: a*a (for signed ints with -fno-wrapv) is always postive
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pinskia at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23471
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/23471] a*a (for signed ints with -fno-wrapv) is always postive
2005-08-19 1:03 [Bug tree-optimization/23471] New: a*a (for signed ints with -fno-wrapv) is always postive pinskia at gcc dot gnu dot org
@ 2005-08-31 16:18 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-08-31 16:18 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-08-31 16:07 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed| |1
Last reconfirmed|0000-00-00 00:00:00 |2005-08-31 16:07:00
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23471
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/23471] a*a (for signed ints with -fno-wrapv) is always postive
[not found] <bug-23471-6528@http.gcc.gnu.org/bugzilla/>
@ 2006-03-01 2:54 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2006-03-01 2:54 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pinskia at gcc dot gnu dot org 2006-03-01 02:54 -------
b_3 = a_1 * a_1;
b_3: VARYING
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2005-12-07 03:01:04 |2006-03-01 02:54:17
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23471
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2006-03-01 2:54 UTC | newest]
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2005-08-19 1:03 [Bug tree-optimization/23471] New: a*a (for signed ints with -fno-wrapv) is always postive pinskia at gcc dot gnu dot org
2005-08-31 16:18 ` [Bug tree-optimization/23471] " pinskia at gcc dot gnu dot org
[not found] <bug-23471-6528@http.gcc.gnu.org/bugzilla/>
2006-03-01 2:54 ` pinskia at gcc dot gnu dot org
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