Re-introduce an IRBuilder optimization that LLVM removed
Re-introduce an IRBuilder optimization that LLVM removed

benlangmuir/swift,benlangmuir/swift,apple/swift,benlangmuir/swift,benlangmuir/swift,glessard/swift,apple/swift,apple/swift,glessard/swift,roambotics/swift,benlangmuir/swift,apple/swift,roambotics/swift,roambotics/swift,roambotics/swift,glessard/swift,apple/swift,glessard/swift,glessard/swift,glessard/swift,benlangmuir/swift,roambotics/swift,roambotics/swift,apple/swift