This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug tree-optimization/51780] New: Missed optimization for ==/!= comparison
- From: "ktietz at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sat, 07 Jan 2012 10:46:18 +0000
- Subject: [Bug tree-optimization/51780] New: Missed optimization for ==/!= comparison
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51780
Bug #: 51780
Summary: Missed optimization for ==/!= comparison
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: ktietz@gcc.gnu.org
Target: *-*-*
Hi,
optimization misses to eliminate addition for 'b' in following code:
extern unsigned int ar[256];
int foo (int a, unsigned int b)
{
int c = ar[a] + b;
int d = (int) b;
return c != d;
}
compiled this code with -O2 we get tree-optimized as follwing:
;; Function foo (foo, funcdef_no=0, decl_uid=1600, cgraph_uid=0)
foo (int a, unsigned int b)
{
int d;
int c;
_Bool D.2717;
int D.2716;
unsigned int D.2715;
unsigned int D.2714;
<bb 2>:
D.2714_2 = ar[a_1(D)];
D.2715_4 = D.2714_2 + b_3(D);
c_5 = (int) D.2715_4;
d_6 = (int) b_3(D);
D.2717_7 = c_5 != d_6;
D.2716_8 = (int) D.2717_7;
<L0>:
return D.2716_8;
}
but optimized variant should be:
;; Function foo (foo, funcdef_no=0, decl_uid=1709, cgraph_uid=0)
foo (int a, unsigned int b)
{
_Bool D.1717;
int D.1716;
unsigned int D.1714;
<bb 2>:
D.1714_2 = ar[a_1(D)];
D.1717_7 = D.1714_2 != 0;
D.1716_8 = (int) D.1717_7;
return D.1716_8;
}