* No tail call optimization in Thumb mode?
@ 2005-06-24 6:15 Kazu Hirata
2005-06-28 9:48 ` Richard Earnshaw
0 siblings, 1 reply; 2+ messages in thread
From: Kazu Hirata @ 2005-06-24 6:15 UTC (permalink / raw)
To: gcc; +Cc: nickc, rearnsha, paul
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.
Thanks in advance,
Kazu Hirata
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: No tail call optimization in Thumb mode?
2005-06-24 6:15 No tail call optimization in Thumb mode? Kazu Hirata
@ 2005-06-28 9:48 ` Richard Earnshaw
0 siblings, 0 replies; 2+ messages in thread
From: Richard Earnshaw @ 2005-06-28 9:48 UTC (permalink / raw)
To: Kazu Hirata; +Cc: gcc, nickc, Paul Brook
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.
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