On Fri, 6 Mar 2015, Jeff Law wrote: > On 03/06/15 06:16, Richard Biener wrote: > > > > This fixes PR63155 and reduces the memory usage at -O0 from reported > > 10GB (couldn't verify/update on my small box) to 350MB (still worse > > compared to 4.8 which needs only 50MB). > > > > It fixes this by no longer computing live info or building a conflict > > graph for coalescing of SSA names flowing over abnormal edges > > (which needs to succeed). > > > > Of course this also removes verification that this coalescing is valid > > (but computing this has quadratic cost). With this it turns > > ICEs into miscompiles. > > > > We could restrict verifying that we can perform abnormal coalescing > > to ENABLE_CHECKING (and I've wanted a verifier pass that can verify > > this multiple times to be able to catch what breaks it and not having > > to work back from out-of-SSA ICEing...). > > > > So any opinion on this patch welcome. > > > > Bootstrap and regtest running on x86_64-unknown-linux-gnu. > > > > Ok for trunk? ;) > > > > Thanks, > > Richard. > > > > 2015-03-06 Richard Biener <rguent...@suse.de> > > > > PR middle-end/63155 > > * tree-ssa-coalesce.c (attempt_coalesce): Handle graph being NULL. > > (coalesce_partitions): Split out abnormal coalescing to ... > > (perform_abnormal_coalescing): ... this function. > > (coalesce_ssa_name): Perform abnormal coalescing without computing > > live/conflict. > I'd personally like to keep the checking when ENABLE_CHECKING. > > I haven't followed this discussion real closely, but I wonder if some kind of > blocking approach would work without blowing up the memory consumption. > There's no inherent reason why we have to coalesce everything at the same > time. We can use a blocking factor and do coalescing on some N number of > SSA_NAMEs at a time.
Yes, that's possible at (quite?) some compile-time cost. Note that we can't really guarantee that the resulting live/conflict problems shrink significantly enough without sorting the coalesces in a different way (not after important coalesces but after their basevars). > I suspect we can select an N that ultimately degenerates into the current "do > everything together" for the common case and only has to iterate over blocks > of SSA_NAMEs in extreme cases. I've attached a patch to the PR that adds such a number N after which we simply stop coalescing. Of course that doesn't work for abnormals where we _must_ coalesce. Thus this patch ... As said, it's simple to keep the checking with ENABLE_CHECKING (I wonder if we should make some of the checking we do a runtime choice rather than a compile-time one...). I'll update the patch. Thanks, Richard.
