https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65689
--- Comment #1 from alalaw01 at gcc dot gnu.org ---
Problem stems from parse_input_constraint (in stmt.c):
if (reg_class_for_constraint (cn) != NO_REGS
|| insn_extra_address_constraint (cn))
*allows_reg = true;
else if (insn_extra_memory_constraint (cn))
*allows_mem = true;
else
{
/* Otherwise we can't assume anything about the nature of
the constraint except that it isn't purely registers.
Treat it like "g" and hope for the best. */
*allows_reg = true;
*allows_mem = true;
}
which causes expand_asm_operands to use (reg/f:DI ...), which fails the
definition of the S constraint. If instead parse_input_constraint set both
allows_reg and allows_mem to false (as it does for e.g. an "i" constraint, via
a special-case), expand_asm_operands would follow the register to its
definition:
(const:DI (plus:DI (symbol_ref:DI ("test") [flags 0x3] <function_decl
0x7fb7c60300 test>)
(const_int 4 [0x4])))
(as also happens with -O), which satisfies the S constraint.
One solution could be to generalize the special case in parse_input_constraint.
