Hi, I'd like to gentle ping this:
https://gcc.gnu.org/pipermail/gcc-patches/2020-December/561413.html BR, Kewen on 2020/12/9 下午5:49, Kewen.Lin via Gcc-patches wrote: > Hi, > > This patch is to treat those new pseudo-to-pseudo copies > after hard-reg-to-pseudo-copy as zero costs. The > justification is that these new copies are closely after > the corresponding hard-reg-to-pseudo-copy insns, register > allocation should be able to coalesce them and get them > eliminated. > > Now these copies follow the normal costing scheme, the > below case dump shows the unexpected combination: > > ``` dump > > Trying 3, 2 -> 13: > 3: r119:DI=r132:DI > REG_DEAD r132:DI > 2: r118:DI=r131:DI > REG_DEAD r131:DI > 13: r128:DI=r118:DI&0xffffffff|r119:DI<<0x20 > REG_DEAD r119:DI > REG_DEAD r118:DI > > Failed to match this instruction: > (set (reg:DI 128) > (ior:DI (ashift:DI (reg:DI 132) > (const_int 32 [0x20])) > (reg:DI 131))) > Successfully matched this instruction: > (set (reg/v:DI 119 [ f2 ]) > (ashift:DI (reg:DI 132) > (const_int 32 [0x20]))) > Successfully matched this instruction: > (set (reg:DI 128) > (ior:DI (reg/v:DI 119 [ f2 ]) > (reg:DI 131))) > allowing combination of insns 2, 3 and 13 > original costs 4 + 4 + 4 = 12 > replacement costs 4 + 4 = 8 > deferring deletion of insn with uid = 2. > modifying insn i2 3: r119:DI=r132:DI<<0x20 > REG_DEAD r132:DI > deferring rescan insn with uid = 3. > modifying insn i3 13: r128:DI=r119:DI|r131:DI > REG_DEAD r131:DI > REG_DEAD r119:DI > deferring rescan insn with uid = 13. > > ``` end dump > > The original insn 13 can work well as rotldi3_insert_3, > so the combination with shift/or isn't better, but the > costing doesn't matches. > > With this patch, we get below instead: > > rejecting combination of insns 2, 3 and 13 > original costs 0 + 0 + 4 = 4 > replacement costs 4 + 4 = 8 > > > Bootstrapped/regtested on powerpc64le-linux-gnu P9. > > Is it reasonable? Any comments are highly appreciated! > > BR, > Kewen > ------ > gcc/ChangeLog: > > * combine.c (new_copies): New static global variable declare/init. > (combine_validate_cost): Consider zero costs from new_copies. > (combine_instructions): Set zero cost for insns in new_copies. > (make_more_copies): Record new pseudo-to-pseudo copies to new_copies. > (rest_of_handle_combine): Call bitmap alloc/free for new_copies. >
