On 10/26/11 15:54, Alan Modra wrote: > On Wed, Oct 26, 2011 at 03:01:01PM +0200, Bernd Schmidt wrote: >> On 10/26/11 14:27, Alan Modra wrote: >>> Committed revision 180522. It turns out that shrink-wrapping isn't as >>> effective as it used to be with the 20110915 based sources I was using >>> originally. povray Ray_In_Bound no longer gets the benefit of shrink >>> wrap, likely due to some cfg optimization. We end up with a simple >>> block that just does r3=1 then jumps to last_bb being reached from >>> blocks that need a prologue as well as blocks that don't. That's >>> enough to kill our current shrink wrap implementation. What we need >>> is something to duplicate these tail blocks.. >> >> Would it work to insert the epilogue on some edges to this R3=1 block, >> and not on the others? > > Wouldn't you need to modify all the target epilogue code? Our > epilogues return.
Not all of them at once - you could require that if a target has a simple_return pattern, the epilogue does not return. But yes, these kinds of complications are a reason why I went for a simple variant first. > I guess the tradeoff between the classic shrink-wrap epilogue scheme > and my duplicate tail idea is whether duplicating tail blocks adds > more code than duplicating epilogues. From what I've seen, the > duplicate tails are generally very small. I guess I should dump out > some info so we can get a better idea. I suppose if one wanted to avoid inserting more than one epilogue for code-size reasons, one could make a new basic block containing the epilogue, and redirect edges as appropriate. Bernd
