A extended value can now be changed to a third form: An alias of another
value. This is like a copy instruction, but implicit in the value table.
Value aliases are used in lieu of use-def chains which would be used to
implement replace-all-uses-with.
Added new DFG methods:
- change_to_alias() changes an existing extended value into an alias.
Primay values can't be changed, replace their definition with a copy
instruction instead.
- resolve_aliases() find the original non-alias value.
- resolve_copies() like resolve_aliases(), but also sees through
copy/spill/fill instructions.
The DataFlowGraph::replace(inst) method returns an instruction builder
that will replace an instruction in-place.
This will be used when transforming instructions, replacing an old
instruction with a new (legal) way of computing its primary value. Since
primary result values are essentially instruction pointers, this is the
only way of replacing the definition of a value.
If secondary result values match the old instruction in both number and
types, they can be reused. If not, added a detach_secondary_results()
method for detaching old secondary values.
The make_inst_results() method now understands direct and indirect
calls, and can allocate result values matching the return types of the
function call.
These two tables are used to keep track of type signatures of function
calls as well as external function references used in direct function
calls.
Also add an ExtFuncData struct representing an external function that
can be called directly.
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'.
