http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60452
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ebotcazou at gcc dot gnu.org
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
If I modify the shorter testcase such that int e[2]; is a static array, then we
don't generate cmove for it, because on:
(mem:SI (const:DI (plus:DI (symbol_ref:DI ("e") <var_decl 0x7ffff19d6098 e>)
(const_int 524288 [0x80000]))) [2 e+524288 S4 A32])
may_trap_or_fault_p returns true (correctly). But in the case of automatic
out-of-bound access we get instead:
(mem/c:SI (plus:DI (reg/f:DI 20 frame)
(const_int 524272 [0x7fff0])) [2 S4 A128])
and there may_trap_or_fault_p really can't (easily) know if it is valid or not,
there is no MEM_EXPR even. This is because in the #c2 testcase as well as the
original one DECL_RTL of e variable is a register, not MEM.
But even if I try:
int a;
__attribute__((noinline, noclone)) void
foo (int *e)
{
asm volatile ("" : : "r" (e) : "memory");
}
int
main ()
{
int e[2] = { 0, 0 }, f = 0;
if (a == 131072)
f = e[a];
foo (e);
return f;
}
where we have:
(mem:SI (plus:DI (reg/f:DI 20 frame)
(const_int 524272 [0x7fff0])) [2 e+524288 S4 A128])
instead and thus from MEM_EXPR we perhaps could find out that it is an out of
bound access, we still always treat all frame based accesses (whatever the
offset is) as non-trapping.
So perhaps we need to handle known out of bound MEMs specially when we find
that fact out (if we want to emit them into the RTL IL at all), one thing is
expansion, another thing if say initially non-constant offset is later
CSEd/forwprop etc. into constant out of bound offset.
Thoughts?
