As observed in CL 54651, these two semantically equivalent bits of code do not always compile equivalently:

if a {
  if b {
   // ...
  }
}

if a && b {
  // ...
}

This issue is to investigate why, and if the latter is systematically better, consider improving the former. Note that 'if a && b' gets special handling at Node -> SSA time; phiopt.go does some further related cleanup, but perhaps not enough.

cc @randall77