https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105051
Bug ID: 105051
Summary: consider not combining malloc + memset to calloc when
inside calloc itself
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: godmar at gmail dot com
Target Milestone: ---
gcc 8.5.0 (and later) just broke our 18-year-old calloc implementation, which
goes like this:
void *
calloc (size_t a, size_t b)
{
/* Calculate block size and make sure it fits in size_t. */
size_t size = a * b;
/* Allocate and zero memory. */
void *p = malloc (size);
if (p != NULL)
memset (p, 0, size);
return p;
}
by producing this ingenuous code sequence:
calloc:
imulq %rsi, %rdi
movl $1, %esi
jmp calloc
I believe that this is due to an optimization whereby a sequence of malloc
followed by memset is transformed into a call to calloc.
My suggestion would be to suppress this optimization inside a function that is
itself called calloc as it leads to an infinite loop.
I'm also curious what the proper work-around is. Is it `-fno-builtin-memset`?
I discovered this in 8.5.0 but Godbolt says it's present in the trunk as of
now:
https://godbolt.org/z/MKMT98qnr
This may be related to Bug #83022
