This was motivated by absence of PrunEH functionality in new PM.
It was decided that a proper way to do PruneEH is to add NoUnwind inference
into PostOrderFunctionAttrs and then perform normal SimplifyCFG on top.
This change generalizes attribute handling implemented for (a removal of)
Convergent attribute, by introducing a generic builder-like class
It registers all the attribute inference requests, storing per-attribute
predicates into a vector, and then goes through an SCC Node, scanning all
the instructions for not breaking attribute assumptions.
The main idea is that as soon all the instructions from all the functions
of SCC Node conform to attribute assumptions then we are free to infer
the attribute as set for all the functions of SCC Node.
It handles two distinct cases of attributes:
- those that might break due to derefinement of the function code
for these attributes we are allowed to apply inference only if all the functions are "exact definitions". Example - NoUnwind.
- those that do not care about derefinement
for these attributes we are allowed to apply inference as soon as we see any function definition. Example - removal of Convergent attribute.
Also in this commit:
- Converted all the FunctionAttrs tests to use FileCheck and added new-PM invocations to them
- FunctionAttrs/convergent.ll test demonstrates a difference in behavior between new and old PM implementations. Marked with FIXME.
- PruneEH tests were converted to new-PM as well, using function-attrs+simplify-cfg combo as intended
- some of "other" tests were updated since function-attrs now infers 'nounwind' even for old PM pipeline
- -disable-nounwind-inference hidden option added as a possible workaround for a supposedly rare case when nounwind being inferred by default presents a problem