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[Bug tree-optimization/31522] [4.3 Regression] False overflow warning with division phi nodes
- From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 10 Apr 2007 07:56:48 -0000
- Subject: [Bug tree-optimization/31522] [4.3 Regression] False overflow warning with division phi nodes
- References: <bug-31522-6528@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #3 from pinskia at gcc dot gnu dot org 2007-04-10 08:56 -------
IR after assert insertion (plus annotate with ranges found):
f (x)
{
int y;
int D.1599;
<bb 2>:
if (x_2(D) <= 4) goto <L2>; else goto <L1>;
<L1>:;
x_7 = ASSERT_EXPR <x_2(D), x_2(D) > 4>; // x_7: [5, +INF]
y_4 = x_7 / 4; // y_4: [1, 536870911]
# y_1 = PHI <1(2), y_4(3)> // y_1: [1, +INF(OVF)]
<L2>:;
D.1599_5 = y_1 <= 0;
return D.1599_5;
}
Can someone explain how we go from the union of [1,1] and [1, 536870911] to
get an inf with an overflow?
Here is another example but this time without a division and just plain obvious
no overflow as everything are just compares:
int f(int x)
{
int y;
if (x>536870911) y =1;
else {
if (x<0) x = 1;
y = x <= 0;
}
return y > 2;
}
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |blocker
Summary|[4.3 Regression] False |[4.3 Regression] False
|overflow warning with |overflow warning with
|division |division phi nodes
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31522