[InstructionCombining] prepareICWorklistFromFunction halts in infinite loop...

[InstructionCombining] prepareICWorklistFromFunction halts in infinite loop with instructions of token type

Summary: This patch fixes a bug in prepareICWorklistFromFunction, where the loop becomes infinite with instructions of token type. The patch checks if the instruction is token type, and if so it updates EndInst with the current instruction.

Reviewers: reames, majnemer

Subscribers: llvm-commits, sanjoy

Differential Revision: http://reviews.llvm.org/D15859

llvm-svn: 256792