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.
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.
Jeff
