Shrink wrapping issues

[Alan Modra]

On Sat, Nov 05, 2011 at 10:50:44AM +0100, Jakub Jelinek wrote:
> >From quick look, f1 isn't shrink-wrapped probably because of the set
> of bb's that need prologue/epilogue around it doesn't end in a return,
> but in a tail call.  Can't we just add a prologue before the bar call
> and throw the epilogue away (normally the epilogue in a function that
> ends only in a tail call is just emitted after the barrier and
> optimized away I think, we could do the same?).

http://gcc.gnu.org/ml/gcc-patches/2011-11/msg00046.html ought to cure
this particular problem.  With that patch, similar code on
powerpc-linux does result in shrink wrapping.

> And f2 is something that IMHO with especially AVX/AVX2 code happens very
> often, the prologue is expensive as it realigns the stack.  The reason
> for that is that until reload we don't know whether something won't be
> spilled on the stack and we need/want 32-byte aligned stack slots
> for that spilling.

Huh?  thread_prologue_and_epilogue is after reload.  So your backend
ought to be able to figure out whether an aligned stack is needed.

-- 
Alan Modra
Australia Development Lab, IBM