On Fri, Oct 16, 2020 at 4:04 PM Martin Liška <mli...@suse.cz> wrote: > > Hello. > > There's another version of the patch that should be based on what > I discussed with Richi and Jakub: > > - the first patch introduces a new option -fbit-tests that analogue to > -fjump-tables > and will control the new if-to-switch conversion pass > > - the second patch adds the pass > - I share code with tree-ssa-reassoc.c (range_entry and init_range_entry) > - a local discovery phase is run first > - later than these local BBs are chained into a candidate list for the > conversion > > I'm also sending transformed chains for 'make all-host' (620 transformations). > Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
-static bool +bool no_side_effect_bb (basic_block bb) { exporting this with this name is dangerous I think because the function seems to allow side-effects in the last stmt - not sure exactly what it tries to allow - there's no comment to that :/ + free (rpo); + free_dominance_info (CDI_DOMINATORS); + + if (!all_candidates.is_empty ()) + mark_virtual_operands_for_renaming (fun); please avoid freeing dominance info when there was no change done (move it to the !all_candidates.is_empty () block). + basic_block bb; + FOR_EACH_BB_FN (bb, fun) + find_conditions (bb, &conditions_in_bbs); + if we didn't find any conditions (or found just one?) we can elide the rest of the function, no? + if_chain *chain = new if_chain (); + chain->m_entries.safe_push (info); + /* Try to find a chain starting in this BB. */ + while (true) + { + if (!single_pred_p (gimple_bb (info->m_cond))) + break; + edge e = single_pred_edge (gimple_bb (info->m_cond)); + condition_info *info2 = conditions_in_bbs.get (e->src); + if (!info2 || info->m_ranges[0].exp != info2->m_ranges[0].exp) + break; + + chain->m_entries.safe_push (info2); + bitmap_set_bit (seen_bbs, e->src->index); + info = info2; + } so while we now record conditions per BB the above doesn't really allow matching a binary tree. What I was thinking of is to record if_chain * per BB as well and look at successors, thus (pseudo-code) if (block ends in cond) if (if_chain on true edge && if_chain on false edge) try merge else if (if_chain on true edge && this-cond tests same var) try merge else if (if_chan on false edge && ...) try merge record if_chain for block where merging would eventually detach the if_chains from the successors. For now we'd just handle the true (and maybe false) edge combos to handle linear chains. Walking reverse RPO (I'm not 100% sure reverse RPO is what we want here, but guess it will work fine for now) will gather chains accordingly. When merging from a successor to a BB fails we push the successor chain to the candidate list. +/* Algorithm of the pass runs in the following steps: + a) We walk basic blocks in DOMINATOR order so that we first reach + a first condition of a future switch. + b) We follow false edges of a if-else-chain and we record chain + of GIMPLE conditions. These blocks are only used for comparison + of a common SSA_NAME and we do not allow any side effect. + c) We remove all basic blocks (except first) of such chain and + GIMPLE switch replaces the condition in the first basic block. + d) We move all GIMPLE statements in the removed blocks into the + first one. */ the overall comment is now a bit out-of-date? Please remove the PHI mapping as I outlined in earlier review. The 0001-Add-fbit-tests-option.patch is OK for trunk. Thanks, Richard. > Thoughts? > Thanks, > Martin