Union-Find Alias Analyses

[fabianbs96]

Adds multiple new Steensgaard-style alias analyses, focusing on high performance and recall.

Main additions:

• LLVMUnionFindAliasSet: Similar to LLVMAliasSet, but featuring the new analyses
• LLVMUnionFindAliasIterator: Compatible with LLVMAliasIteratorRef
• compute[...]SensUnionFindAA(): Functions to invoke the new analyses directly, without going through LLVMUnionFindAliasSet.
• LLVMPAGBuilder : Utility to build pointer-assignment graphs with different strategies that can be plugged-in. This class may be reused for other analyses as well.

The currently implemented POC analyses are integrated into phasar-cli as --alias-analysis=union-find and the following analysis variants:

  --union-find-aa=<value>       - The union-find alias analysis type to use (default: ctx-ind-sens)
    =ctx-sens                   -   Context-sensitive analysis with k=1 heap-cloning
    =ind-sens                   -   Pointer-indirection-sensitive analysis with k=5 heap-cloning
    =ctx-ind-sens               -   Intersection of ctx-sens and ind-sens
    =botctx-sens                -   Unbounded context-sensitive analysis, but only provides function-local results
    =botctx-ind-sens            -   Intersection of botctx-sens and ind-sens

As initial estimation on the results quality, we ran the new analyses on SVF's PTABen test suite. You can find details here.