This fixes 2 bugs and adds corresponding tests. Both related to unreachable
blocks. One occured in the `WTOCompare` construction, which assumed the size of
the order was the same as the number of blocks in the CFG, which isn't true when
some blocks are unreachable. The other assumed predecessor pointers were
non-null, which can be false for blocks with unreachable predecessors.
Differential Revision: https://reviews.llvm.org/D157033
This patch adds support for building a weak topological ordering (WTO) of the
CFG blocks, based on a limit flow graph constructed via (repeated) interval
partitioning of the CFG.
This patch is part 2 of 2 for adding WTO support.
Differential Revision: https://reviews.llvm.org/D153058
Adds support for the classic dataflow algorithm that partitions a flow graph
into distinct intervals. C.f. Dragon book, pp. 664-666.
A version of this algorithm exists in LLVM (see llvm/Analysis/Interval.h and
related files), but it is specific to LLVM, is a recursive (vs iterative)
algorithm, and uses many layers of abstraction that seem unnecessary for CFG
purposes.
This patch is part 1 of 2. The next patch will generalize the code to work on
intervals, to support computation of the limit flow graph.
Differential Revision: https://reviews.llvm.org/D152263
