On Fri, 2005-06-24 at 07:15, Kazu Hirata wrote: > Hi, > > Why is tail call optimization for Thumb disabled on GCC? I am > wondering if this is a TODO item or something that we cannot do > intrinsically. > > "The ARM-THUMB Procedure Call Standard" says "No tail continuation in > Thumb-state" several times in its figures and measurements, but the > document doesn't explicitly forbid tail call optimization for Thumb. >
There's no prohibition on it, but the thumb-1 branch instruction has a range of only +/- 2kB (which is too small to reach an arbitrary target address in an image) and we currently don't support tail-calls via a register for either ARM or Thumb state. If we *knew* that the target address would be reachable, then we could probably use a tail-call, but in practice I don't think we can. R.
