GNU Info

(gcc-295.info)No Constraints

---

Prev: Machine Constraints Up: Constraints

---

Enter node , (file) or (file)node

Not Using Constraints
---------------------

   Some machines are so clean that operand constraints are not
required.  For example, on the Vax, an operand valid in one context is
valid in any other context.  On such a machine, every operand
constraint would be `g', excepting only operands of "load address"
instructions which are written as if they referred to a memory
location's contents but actual refer to its address.  They would have
constraint `p'.

   For such machines, instead of writing `g' and `p' for all the
constraints, you can choose to write a description with empty
constraints.  Then you write `""' for the constraint in every
`match_operand'.  Address operands are identified by writing an
`address' expression around the `match_operand', not by their
constraints.

   When the machine description has just empty constraints, certain
parts of compilation are skipped, making the compiler faster.  However,
few machines actually do not need constraints; all machine descriptions
now in existence use constraints.