Show compiler's estimate of branch/block probabilities

Aside from Profile-Guided Optimization (PGO), branch probabilities can be estimated from control flow analysis or set explicitly with builtinexpectwith_probability directive. I'm not aware of any existing fancy tool to nicely report these estimated probabilities but stock llvm tooling is sufficient to take a peek.

Example program calculating Fibonacci sequence:

// test.cpp
int fib(int n)
{
    if (n  %6 probability is 0x40000000 / 0x80000000 = 50.00%
  edge %1 -> %8 probability is 0x40000000 / 0x80000000 = 50.00%
  edge %6 -> %16 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]
  edge %8 -> %16 probability is 0x80000000 / 0x80000000 = 100.00% [HOT edge]