Stack slots for outgoing arguments can be reused between function calls.
Add a list of outgoing argument stack slots allocated so far, and
provide a `get_outgoing_arg()` method which will reuse any outgoing
stack slots with matching size and offset.
Function arguments that don't fit in registers are passed on the stack.
Create "incoming_arg" stack slots representing the stack arguments, and
assign them to the value arguments during spilling.
The offset is relative to the stack pointer in the calling function, so
it excludes the return address pushed by the call instruction itself on
Intel ISAs.
Change the ArgumentLoc::Stack offset to an i32, so it matches the stack
slot offsets.
Use a new StackSlots struct to keep track of a function's stack slots
instead of just an entity map. This let's us build more internal data
structures for tracking the stack slots if necessary.
Start by adding a make_spill_slot() function that will be used by the
register allocator.
Add a StackSlotKind enumeration to help keep track of the different
kinds of stack slots supported:
- Incoming and outgoing function arguments on the stack.
- Spill slots and locals.
Change the text format syntax for declaring a stack slot to use a kind
keyword rather than just 'stack_slot'.
Give these crates each a more standard directory layout with sources in
a 'src' sub-sirectory and Cargo.toml in the top lib/foo directory.
Add license and description fields to each.
The build script for the cretonne crate now lives in
'lib/cretonne/build.rs' separating it from the normal library sources
under 'lib/cretonne/src'.
