The issue was raised here: https://reviews.llvm.org/D60903#1472783
The function Instruction::updateProfWeight is only used for CallInst in profile update. From the current interface, it is very easy to think that the function can also be used for branch instruction. However, Branch instruction does't need the scaling the function provides for branch_weights and VP (value profile), in addition, scaling may introduce inaccuracy for branch probablity.
The patch moves the function updateProfWeight from Instruction class to CallInst to remove the confusion. The patch also changes the scaling of branch_weights from a loop to a block because we know that ProfileData for branch_weights of CallInst will only have two operands at most.