Retry: [BPI] Use a safer constructor to calculate branch probabilities
BPI may trigger signed overflow UB while computing branch probabilities for
cold calls or to unreachables. For example, with our current choice of weights,
we'll crash if there are >= 2^12 branches to an unreachable.
Use a safer BranchProbability constructor which is better at handling fractions
with large denominators.
Changes since the initial commit:
- Use explicit casts to ensure that multiplication operands are 64-bit
ints.
rdar://problem/
29368161
Differential Revision: https://reviews.llvm.org/D27862
llvm-svn: 290022