[InstCombine] Generalize and consolidate phi translation check (#106051)

The foldOpIntoPhi() transforms requires all operands to be
phi-translatable. This can be the case either because they are phi nodes
in the same block, or because the operand dominates the block.

Currently, most callers of foldOpIntoPhi() satisfy this pre-condition by
requiring a constant operand, which trivially dominates everything. Only
selects had handling for variable operands.

Move this logic into foldOpIntoPhi(), so things are handled correctly if
other callers are generalized. Also make the implementation a bit more
general by querying the dominator tree.

0 files changed, 0 insertions, 0 deletions