This patch modifies the common indirect call promotion utilities by by exposing and using an unconditional call promotion interface. These changes are meant to accommodate the planned use case in D39869. The unconditional promotion interface (i.e., call promotion without creating an if-then-else) can be used if it's known that an indirect call has only one possible callee. The existing conditional promotion interface uses this unconditional interface to promote an indirect call after it has been versioned and placed within the "then" block.
A consequence of unconditional promotion is that the fix-up operations for phi nodes in the normal destination of invoke instructions are changed. This is necessary because the existing implementation assumed that an invoke had been versioned, creating a "merge" block where a return value bitcast could be placed. In the new implementation, the edge between a promoted invoke's parent block and its normal destination is split if needed to add a bitcast for the return value. If the invoke is also versioned, the phi node merging the return value of the promoted and original invoke instructions is placed in the "merge" block.