Hi all,
I'm trying, without success, to disable loop unrolling when compiling a
program with -O3 with gcc (4.4, but I see the same problem with 4.3).
The program is the following one:
volatile int v;
void func()
{
int i;
for( i=0; i8; ++i ) {
v=0;
}
}
I compile it with the
Just out of curiousity: why do you care about the resulting assembly?
It's a strong indication that you are doing something wrong :)
I would try to set i to volatile or to an extern to trick the compiler
to drop the optimization (if the flags don't work).
--Aviv
2009/12/21 Shachar Shemesh
Aviv Greenberg wrote:
Just out of curiousity: why do you care about the resulting assembly?
It's a strong indication that you are doing something wrong :)
First, we have found several bugs in GCC as a result of caring about
the assembly. Lets agree that it's an indication that someone is
This is what i get if i set i to be volatile in gcc 4.3.1 with -O3:
0: 55 push %ebp
1: 89 e5 mov%esp,%ebp
3: 83 ec 10sub$0x10,%esp
6: c7 45 fc 00 00 00 00movl $0x0,-0x4(%ebp)
d: 8b 45 fc
On Monday 21 December 2009 14:00:39 Shachar Shemesh wrote:
Where it gets worrying is when I try to cancel loop unrolling. I tried
-fno-unroll-loops and -fno-peel-loops, to no effect. I even tried
messing with the --param option (max-unrolled-insns, max-unroll-times,
max-peel-times) to no
Also, i tried grepping for loop and then negate all loop related params:
linux-gec2:~/projects/lu # gcc -c -O3 -fno-align-loops
-fno-move-loop-invariants -fno-peel-loops -fno-prefetch-loop-arrays
-fno-rerun-cse-after-loop -fno-reschedule-modulo-scheduled-loops
-fno-tree-loop-im
2009/12/21 Shachar Shemesh shac...@shemesh.biz:
Hi all,
I'm trying, without success, to disable loop unrolling when compiling a
program with -O3 with gcc (4.4, but I see the same problem with 4.3).
I am actually very surprized that -O3 unrolls loops. It is not
supposed to. The idea to include
Dotan Shavit wrote:
On Monday 21 December 2009 14:00:39 Shachar Shemesh wrote:
Where it gets worrying is when I try to cancel loop unrolling. I tried
-fno-unroll-loops and -fno-peel-loops, to no effect. I even tried
messing with the --param option (max-unrolled-insns, max-unroll-times,
