On Sat, Apr 19, 2025 at 08:33:48PM -0700, Andrew Pinski wrote:
> > + {
> > + tree other_value = NULL_TREE;
> > + /* If we have a function call that we know the return value is
> > the same
> > + as the argument, try the argument too. */
> > + int flags = gimple_call_return_flags (call);
> > + if ((flags & ERF_RETURNS_ARG) != 0
> > + && (flags & ERF_RETURN_ARG_MASK) < gimple_call_num_args
> > (call))
> > + other_value = gimple_call_arg (call, flags &
> > ERF_RETURN_ARG_MASK);
I think this needs to verify that other_value's type is uselessly
convertible to TREE_TYPE (ret_var).
Because just relying on operand_equal_p returning false otherwise wouldn't
work.
E.g. if call is memcpy, and you pass say NULL as the first argument to it
(and some pointer and some non-constant as last), but the function returns
unsigned char 0, you don't want to do a tail call just because NULL is equal
to that unsigned char 0. Sure, on lots of targets/ABIs that will in this
particular case work fine, but isn't guaranteed to work on all.
Perhaps on 32-bit arches if function returns 0ULL?
Jakub
