Consider the following program fragment:
char *p;
int i;
for (i=0; i<10; i++)
{
p = malloc(20);
foo(p,i);
free(p);
}
}
The loop could be simplified into
p = malloc(20);
for (i=0; i<10; i++)
foo(p,i);
free(p);
This would reduce the overhead for memory allocation
considerably.
A more challenging case is to change
for (i=0; i<10; i++)
{
p = malloc(2*i+2);
foo(p,i);
free(p);
}
into
p = malloc(20);
for (i=0; i<10; i++)
foo(p,i);
free(p);
because the amount of memory allocated has an upper bound.
This is probably not a big win for straight C code. For languages
which generate temporary arrays at runtime, such as Fortran, it
could mean a significant reduction in memory management overhead.
--
Summary: move memory allocation out of a loop
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P2
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: tkoenig at gcc dot gnu dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21046
