[SimplifyCFG] Extend SimplifyResume to handle phi of trivial landing pad.

[SimplifyCFG] Extend SimplifyResume to handle phi of trivial landing pad.

Summary: Currently SimplifyResume can convert an invoke instruction to a call instruction if its landing pad is trivial. In practice we could have several invoke instructions with trivial landing pads and share a common rethrow block, and in the common rethrow block, all the landing pads join to a phi node. The patch extends SimplifyResume to check the phi of landing pad and their incoming blocks. If any of them is trivial, remove it from the phi node and convert the invoke instruction to a call instruction.

Reviewers: hfinkel, reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13718

llvm-svn: 251061