A priory, an EBB argument value only gets an affinity if it is used
directly by a non-ghost instruction. A use by a branch passing arguments
to an EBB doesn't count.
When an EBB argument value does have an affinity, the values passed by
all the predecessors must also have affinities. This can cause EBB
argument values to get affinities recursively.
- Add a second pass to the liveness computation for propagating EBB
argument affinities, possibly recursively.
- Verify EBB argument affinities correctly: A value passed to a branch
must have an affinity only if the corresponding EBB argument value in
the destination has an affinity.
* Replace a single-character string literal with a character literal.
* Use is_some() instead of comparing with Some(_).
* Add code-quotes around type names in comments.
* Use !...is_empty() instead of len() != 0.
* Tidy up redundant returns.
* Remove redundant .clone() calls.
* Remove unnecessary explicit lifetime parameters.
* Tidy up unnecessary '&'s.
* Add parens to make operator precedence explicit.
* Use debug_assert_eq instead of debug_assert with ==.
* Replace a &Vec argument with a &[...].
* Replace `a = a op b` with `a op= b`.
* Avoid unnecessary closures.
* Avoid .iter() and .iter_mut() for iterating over containers.
* Remove unneeded qualification.
This value affinity doesn't mean "whatever", it means that the value
does not interact with any real instructions, where "real" means
instructions that have a legal encoding.
Update the liveness verifier to check this property:
- Encoded instructions can only use real values.
- Encoded instructions define real values.
- Ghost instructions define ghost values.
This means that we can verify the basics with verify_context before
moving on to verifying the liveness information.
Live ranges are now verified immediately after computing them and after
register allocation is complete.
The liveness verifier will check that the live ranges are consistent
with the function. It runs as part of the register allocation pipeline
when enable_verifier is set.
The initial implementation checks the live ranges, but not the
ISA-specific constraints and affinities.
