if-conversion. The RemoveExtraEdges function doesn't work for blocks that
end with unanalyzable branches, so in those cases, the "extra" edges must
be explicitly removed. The CopyAndPredicateBlock and MergeBlocks methods
can also avoid copying successor edges due to branches that have already
been removed. The latter case is especially helpful when MergeBlocks is
called for handling "diamond" if-conversions, where otherwise you can end
up with some weird intermediate states in the CFG. Unfortunately I've
been unable to find cases where this cleanup actually makes a significant
difference in the code. There is one test where we manage to remove an
empty block at the end of a function. Radar 6911268.
llvm-svn: 106939
tail merging support to handle more cases.
- Recognize several cases where tail merging is beneficial even when
the tail size is smaller than the generic threshold.
- Make use of MachineInstrDesc::isBarrier to help detect
non-fallthrough blocks.
- Check for and avoid disrupting fall-through edges in more cases.
llvm-svn: 86871
