Four ways of coding a conditional assignment yields 1 conditional move using
gcc 3.4.5 20051201 (Red Hat 3.4.5-2). gcc 4.0.2 20051130 (Red Hat 4.0.2-14.EL4)
produces none. IMHO, four cmov's should have been produced. I further expect
all four functions to generates the exact same code.
All recent new commercial compilers tested generates four cmov's:
- intel 8.1, 9.0, and 9.1
- pgi 5.2, 6.0, 6.1, and 6.2
- pathscale 2.1, 2.2, 2.3, 2.4
Version-Release number of selected component (if applicable):
How reproducible:
allways
Steps to Reproduce:
gcc -O2 -S if_conversion.c;egrep cmov\|^[a-d]: if_conversion.s
Actual results:
a:
b:
c:
d:
cmove %ecx, %esi
Expected results:
One cmovX per function, four in total.
Here is the source code:
---------------------------------------------------------------------
/* if construct, near obvious cse */
int a(int c, int a, int b, int o) {
int r;
if (c) {
r = a - b;
} else {
r = a + o - b;
}
return r;
}
/* if construct, absolute obvious cse */
int b(int c, int a, int b, int o) {
int r;
if (c) {
r = a - b;
} else {
r = a - b + o;
}
return r;
}
/* conditional assignment, near obvious cse */
int c(int c, int a, int b, int o) {
int r;
r = (c) ? a - b : a + o - b;
return r;
}
/* conditional assignment, absolute obvious cse */
int d(int c, int a, int b, int o) {
int r;
r = (c) ? a - b : a - b + o;
return r;
}
---------------------------------------------------------------------
--
Summary: Missing if-conversion. If-conversion dependent on
operand order. Inconsistent if-conversion.
Product: gcc
Version: 3.4.5
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: Hakon dot Bugge at scali dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29144
