On Mon, Oct 31, 2016 at 4:35 PM, Segher Boessenkool <seg...@kernel.crashing.org> wrote: > On Mon, Oct 31, 2016 at 04:09:48PM +0100, Steven Bosscher wrote: >> On Sun, Oct 30, 2016 at 8:10 PM, Segher Boessenkool wrote: >> > This patch solves this problem by simply running the >> > duplicate_computed_gotos >> > pass again, as long as it does any work. The patch looks much bigger than >> > it is, because I factored out two routines to simplify the control flow. >> >> It's made the patch a bit difficult to read. Condensing it a bit... > > Well, it would have a goto crossing a loop, or two gotos crossing each > other, otherwise. I should have done it as two patches I guess (first > factor, then change). > >> > + for (;;) >> > { >> > + if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1) >> > + return 0; >> >> This test should not be needed in the loop. This pass can never >> collapse the function to a single basic block. > > Yeah maybe, but that relies on quite a few assumptions. This is strictly > an optimisation anyway, will move it outside the loop. > >> > + basic_block bb; >> > + FOR_EACH_BB_FN (bb, fun) >> > + { >> > + /* Build the reorder chain for the original order of blocks. */ >> > + if (bb->next_bb != EXIT_BLOCK_PTR_FOR_FN (fun)) >> > + bb->aux = bb->next_bb; >> > + } >> > >> > + duplicate_computed_gotos_find_candidates (fun, candidates, >> > max_size); >> > >> > + bool changed = false; >> > + if (!bitmap_empty_p (candidates)) >> > + changed = duplicate_computed_gotos_do_duplicate (fun, candidates); >> > >> > + if (changed) >> > + fixup_partitions (); >> > + >> > + cfg_layout_finalize (); >> >> I don't think you have to go into/out-of cfglayout mode for each iteration. > > Yeah probably. I was too lazy :-) It needs the cleanup_cfg every > iteration though, I was afraid that interacts.
Ick. Why would it need a cfg-cleanup every iteration? I fear this is quadratic complexity in the number of edges to the compgoto block (and the size of the function). Can't the unfactoring perform the "cleanup" we rely on here? >> > /* Merge the duplicated blocks into predecessors, when possible. */ >> > + if (changed) >> > + cleanup_cfg (0); >> > + else >> > + break; >> > } >> >> Maybe a gcc_assert that the loop doesn't iterate more often than num_edges? > > Good plan (num blocks even). > > Thanks, > > > Segher