On Sun, Aug 12, 2012 at 11:49 PM, Steven Bosscher <stevenb....@gmail.com> wrote: > Hello, > > This patch tried to use non-clearing memory allocation where possible. > This is especially important for very large functions, when arrays of > size in the order of n_basic_blocks or num_ssa_names are allocated to > hold sparse data sets. For such cases the overhead of memset becomes > measurable (and even dominant for the time spent in a pass in some > cases, such as the one I recently fixed in ifcvt.c). > > This cuts off ~20% of the compile time for the test case of PR54146 at > -O1. Not bad for a patch that basically only removes a bunch of > memsets. > > I got another 5% for the changes in tree-ssa-loop-manip.c. A loop over > an array with num_ssa_names there is expensive and unnecessary, and it > helps to stuff all bitmaps together on a single obstack if you intend > to blow them all away at the end (this could be done in a number of > other places in the compiler). Clearing livein at the end of > add_exit_phis_var also reduces peak memory with ~250MB at that point > in the passes pipeline (only to blow up from ~1.5GB peak memory in the > GIMPLE optimizers to ~3.6 GB in expand, and to ~8.6GB in IRA, but hey, > who's counting? :-) > > Actually, the worst cases are not fixed with this patch. That'd be IRA > (which consumes ~5GB on the test case, out of 8GB total), and > tree-PRE. > > The IRA case looks like it may be hard to fix: Allocating multiple > arrays of size O(max_regno) for every loop in init_loop_tree_node. > > The tree-PRE case is one where the avail arrays are allocated and > cleared for every PRE candidate. This looks like a place where a > pointer_map should be used instead. I'll tackle that later, when I've > addressed more pressing problems in the compilation of the PR54146 > test case.
Hmm, or eaiser, use a vector of size (num_bb_preds) and index it by edge index. > This patch was bootstrapped&tested on powerpc64-unknown-linux-gnu. OK for > trunk? Ok with adjusting the PRE comments according to the above. Thanks, Richard. > Kudos to the compile farm people, without them I couldn't even hope to > get any of this work done! > Ciao! > Steven
