https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86247
Bug ID: 86247
Summary: warning on alloca within a loop overly restrictive for
constant loops
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The usability of the-Walloca-larger-than= warnings could be improved by taking
into consideration the product of the upper bound on the number of iterations
of the loop and the alloca argument. For example, the loop in the following
test case effectively results in allocating just 32 * 17 or 544 bytes, well
below the 4K limit set by the -Walloca-larger-than=4096 option. The warning
could be avoided in this case.
$ cat c.c && gcc -S -O2 -Wall -Wextra -Walloca-larger-than=4096 c.c
void f (void*, ...);
void g (void)
{
for (int i = 0; i != 17; ++i)
f (__builtin_alloca (32));
}
c.c: In function ‘g’:
c.c:6:5: warning: use of ‘alloca’ within a loop [-Walloca-larger-than=]
f (__builtin_alloca (32));
^~~~~~~~~~~~~~~~~~~~~~~~~
