https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114185
Bug ID: 114185
Summary: Missed tail-call optimization due to an argument whose
address is taken
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: dizhao at os dot amperecomputing.com
Target Milestone: ---
GCC (with "-Ofast") doesn't perform tail call optimization on a function like:
long test_func (long n, unsigned long u64arg,
unsigned int u32arg, unsigned long *p)
{
if (n > 0)
return test_func (n - 1, u64arg + (unsigned long) u32arg, u32arg, p);
else
return &u64arg - p;
}
llvm can optimize the tail call.
GCC gave up tail call optimization, because the following check in
find_tail_calls() failed on argument "u64arg":
/* The parameter should be a real operand, so that phi node
created for it at the start of the function has the meaning
of copying the value. This test implies is_gimple_reg_type
from the previous condition, however this one could be
relaxed by being more careful with copying the new value
of the parameter (emitting appropriate GIMPLE_ASSIGN and
updating the virtual operands). */
if (!is_gimple_reg (param))
break;
The check was to fix this ICE:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93487 . But in this case,
"&u64arg" won't be used in PHI argument, so it seems ok for tail call
optimization. (BTW, I tried current GCC trunk on the example code in PR 93487,
but haven't encounter the ICE with that check removed, because the PHI
arguments are "&y" and "&x" now.)
