On 08/05/2013 05:18 AM, David Malcolm wrote: > So I *think* the most efficient traversal is to do this first (with a > suitable comment): > > for (int i = passes_by_id_size ; i > 0; ) > ::gt_ggc_mx (passes_by_id[--i]); > > That ought to visit all of the passes without triggering recursion > (unless someone does something weird to the pass structure in a plugin).
Reasonable. > I'm nervous about omitting the traversal for other pointers the class > has (though I *think* the passes by id array captures it all) so for > completeness I'd prefer to then to also do it for all of: > > ::gt_ggc_mx (all_passes); > ::gt_ggc_mx (all_small_ipa_passes); > ::gt_ggc_mx (all_lowering_passes); > ::gt_ggc_mx (all_regular_ipa_passes); > ::gt_ggc_mx (all_lto_gen_passes); > ::gt_ggc_mx (all_late_ipa_passes); > > #define INSERT_PASSES_AFTER(PASS) > #define PUSH_INSERT_PASSES_WITHIN(PASS) > #define POP_INSERT_PASSES() > #define NEXT_PASS(PASS, NUM) ::gt_ggc_mx (PASS ## _ ## NUM); > #define TERMINATE_PASS_LIST() > > #include "pass-instances.def" > > #undef INSERT_PASSES_AFTER > #undef PUSH_INSERT_PASSES_WITHIN > #undef POP_INSERT_PASSES > #undef NEXT_PASS > #undef TERMINATE_PASS_LIST > > Is it standard in handwritten GC code to omit traversals based on this > higher-level knowledge? Presumably it warrants a source comment? > (having spent too much time lately debugging PCH issues I'm nervous > about trying to optimize this). It's something that we should think about when doing any kind of GC. The deep recursion has bitten us before, and lead to the chain_next and chain_prev annotations for GTY. > AIUI we could do similar optimizations in the PCH object-noting hook, > but can't do similar optimizations in the PCH *op* hook, since every > field needs to reconstructed when reading the data back from disk. Correct. r~
