Hi, I'd like to gentle ping this:
https://gcc.gnu.org/pipermail/gcc-patches/2020-December/562015.html BR, Kewen on 2020/12/16 下午4:49, Kewen.Lin via Gcc-patches wrote: > Hi, > > When I was investigating unsigned int vec_init issue on Power, > I happened to find there seems something we can enhance in how > combine pass invalidate last_set (set last_set_invalid nonzero). > > Currently we have the check: > > if (!insn > || (value && rsp->last_set_table_tick >= label_tick_ebb_start)) > rsp->last_set_invalid = 1; > > which means if we want to record some value for some reg and > this reg got refered before in a valid scope, we invalidate the > set of reg (last_set_invalid to 1). It avoids to find the wrong > set for one reg reference, such as the case like: > > ... op regX // this regX could find wrong last_set below > regX = ... // if we think this set is valid > ... op regX > > But because of retry's existence, the last_set_table_tick could > be set by some later reference insns, but we see it's set due > to retry on the set (for that reg) insn again, such as: > > insn 1 > insn 2 > > regX = ... --> (a) > ... op regX --> (b) > > insn 3 > > // assume all in the same BB. > > Assuming we combine 1, 2 -> 3 sucessfully and replace them as two > (3 insns -> 2 insns), retrying from insn1 or insn2 again: > it will scan insn (a) again, the below condition holds for regX: > > (value && rsp->last_set_table_tick >= label_tick_ebb_start) > > it will mark this set as invalid set. But actually the > last_set_table_tick here is set by insn (b) before retrying, so it > should be safe to be taken as valid set. > > This proposal is to check whether the last_set_table safely happens > after the current set, make the set still valid if so. > > Bootstrapped/regtested on powerpc64le-linux-gnu (P9), > aarch64-linux-gnu and x86_64-pc-linux-gnu. > > Full SPEC2017 building shows this patch gets more sucessful combines > from 1902208 to 1902243 (trivial though). > > Any comments are highly appreciated! > > BR, > Kewen > ----- > > gcc/ChangeLog: > > * combine.c (struct reg_stat_type): New member > last_set_table_luid. > (update_table_tick): Add one argument for insn luid and > set last_set_table_luid with it. > (record_value_for_reg): Adjust the condition to set > last_set_invalid nonzero. > BR, Kewen
