4221 on new codegen

[Edward Z. Yang]

Current theory:

  c1jj:
      _s1ep::I32 = I32[(slot<_s1ep::I32> + 4)];   // CmmAssign
      _s1fP::I32 = I32[(slot<_s1fP::I32> + 4)];   // CmmAssign
      // outOfLine should follow:
      _s1eq::F64 = F64[_s1fP::I32 + 3];   // CmmAssign
      I32[(young<c1jh> + 4)] = c1jh;   // CmmStore
      foreign call "ccall" arg hints:  [PtrHint,]  result hints:  [] call_fn_blob(...) returns to c1jh args: ([_s1ep::I32,
                                                                                                               _s1eq::F64]) ress: ([_s1ev::F64]) with update frame 4;   // CmmForeignCall
  c1jh:
      _s1ev::F64 = F64[(slot<_s1ev::F64> + 8)];   // CmmAssign
      // emitReturn: Sequel: Assign
      _s1ev::F64 = _s1ev::F64;   // CmmAssign
      F64[(slot<_s1ev::F64> + 8)] = _s1ev::F64;   // CmmStore
      goto u1Ak;   // CmmBranch

Note the line immediately after c1jh, where we reload the ostensibly
spilled _s1ev back into a register. Except that it was never spilled
there in the first place, and we just clobbered the real value. Oops.

Is this interpretation correct?

Edward