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. > (How many edges of each kind are there?) In the povray case there was one edge of each kind, but I have seen other cases where there were 4 edges from blocks needing no prologue and 2 edges from blocks needing a prologue. I can't tell you what the testcase was now; It was something I looked at when ironing out bugs in my code. You wouldn't believe how many ways it is possible to write buggy cfg manipulation code.. 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. -- Alan Modra Australia Development Lab, IBM