On Sat, 2023-11-11 at 13:12 -0700, Jeff Law wrote: > > > On 8/14/23 05:22, Jin Ma wrote: > > CLOBBER and USE does not represent real instructions, but in the > > process of pipeline optimization, they will wait for transmission > > in ready list like other insns, without considering resource > > conflicts and cycles. This results in a multi-issue CPU architecture > > that can be issued at any time if other regular insns have resource > > conflicts or cannot be launched for other reasons. As a result, > > its position is advanced in the generated insns sequence, which > > will affect register allocation and often lead to more redundant > > mov instructions. > > > > A simple example: > > https://github.com/majin2020/gcc-test/blob/master/test.c > > This is a function in the dhrystone benchmark. > > > > https://github.com/majin2020/gcc-test/blob/0b08c1a13de9663d7d9aba7539b960ec0607ca24/test.c.299r.sched1 > > This is a log of the pass 'sched1' When -mtune=rocket but issue_rate > > == 2. > > > > The pipeline is: > > ;; | insn | prio | > > ;; | 17 | 3 | r142=a0 alu > > ;; | 14 | 0 | clobber r136 nothing > > ;; | 13 | 0 | clobber a0 nothing > > ;; | 18 | 2 | r143=a1 alu > > ... > > ;; | 12 | 0 | a0=r136 alu > > ;; | 15 | 0 | use a0 nothing > > > > In this log, insn 13 and 14 are much ahead of schedule, which risks > > generating > > redundant mov instructions, which seems unreasonable. > > > > Therefore, I submit patch again on the basis of the last review > > opinions to try to solve this problem. > > > > https://github.com/majin2020/gcc-test/commit/efcb43e3369e771bde702955048bfe3f501263dd#diff-805031b1be5092a2322852a248d0b0f92eef7cad5784a8209f4dfc6221407457L189 > > This is the diff log of shed1 after patch is added. > > > > The new pipeline is: > > ;; | insn | prio | > > ;; | 17 | 3 | r142=a0 alu > > ... > > ;; | 10 | 0 | [r144]=r141 alu > > ;; | 13 | 0 | clobber a0 nothing > > ;; | 14 | 0 | clobber r136 nothing > > ;; | 12 | 0 | a0=r136 alu > > ;; | 15 | 0 | use a0 nothing > > > > gcc/ChangeLog: > > * haifa-sched.cc (use_or_clobber_starts_range_p): New. > > (prune_ready_list): USE or CLOBBER should delay execution > > if it starts a new live range. > OK for the trunk. It doesn't look like you have write access and I > don't see anything about what testing was done. Standard practice is > to > do a bootstrap and regression test on a primary platform such as x86, > aarch64, ppc64. > > I went ahead and did a bootstrap and regression test on x86_64, then > pushed this to the trunk.
Unfortunately this patch has triggered a bootstrap comparison failure on loongarch64-linux-gnu: https://gcc.gnu.org/PR112497. -- Xi Ruoyao <xry...@xry111.site> School of Aerospace Science and Technology, Xidian University
