Re: [PATCH v4 4/5] RISC-V: Add macro-fusion pair recognition

[Jeffrey Law]

On 8/6/2026 9:11 AM, Jin Ma wrote:
Hi Jeff,

On 7/29/2026 1:17 AM, Jin Ma wrote:
Add recognition for the following macro-fusion pairs:

    RISCV_FUSE_SUB_SEQZ        - sub/subw + seqz/snez
    RISCV_FUSE_ADD_LD          - add type + integer load
    RISCV_FUSE_ADD_ST          - add type + integer store
    RISCV_FUSE_ADD_ANDI        - add/addi type + andi type
    RISCV_FUSE_ANDI_ADD        - andi type + add/addi type
    RISCV_FUSE_LOGIC_LOGIC     - logic + logic
    RISCV_FUSE_SLLI_SRLI       - slli/slliw + srli/srliw
    RISCV_FUSE_SRLI_ADD        - srli/srliw + add type
    RISCV_FUSE_PREINDEX_LD     - addi type + load
    RISCV_FUSE_PREINDEX_ST     - addi type + store
    RISCV_FUSE_POSTINDEX_LD    - load + addi type
    RISCV_FUSE_POSTINDEX_ST    - store + addi type
    RISCV_FUSE_LDST_PAIR_INC   - ascending integer load/store pair
    RISCV_FUSE_LDST_PAIR_DEC   - descending integer load/store pair
    RISCV_FUSE_FLDFST_PAIR_INC - ascending FP load/store pair
    RISCV_FUSE_FLDFST_PAIR_DEC - descending FP load/store pair

Leave the pairs disabled by default and mark positive checks as XFAIL.

gcc/ChangeLog:

  * config/riscv/riscv-fusion.cc: Include insn-attr.h.
  (riscv_fusion_same_source_p, riscv_set_is_addw_p,
  riscv_set_is_word_add_p, riscv_set_is_addiw_p, riscv_insn_is_mv_li_p,
  riscv_insn_is_addi_type_p, riscv_insn_is_nonword_addi_type_p,
  riscv_insn_is_add_type_p, riscv_insn_is_add_addi_p,
  riscv_insn_is_sub_type_p, riscv_insn_is_andi_type_p,
  riscv_insn_is_logical_type_p, riscv_set_is_slli_p,
  riscv_set_is_slliw_p, riscv_set_is_srli_p, riscv_set_is_srliw_p,
  riscv_set_is_word_shift_p, riscv_fusion_extract_address,
  riscv_fusion_load_store, riscv_insn_is_load_store_type_p): New
  helper functions.
  (riscv_fuse_sub_seqz, riscv_fuse_add_andi, riscv_fuse_add_ldst_1,
  riscv_fuse_add_ld, riscv_fuse_add_st, riscv_fuse_andi_add,
  riscv_fuse_logic_logic, riscv_fuse_slli_srli, riscv_fuse_srli_add,
  riscv_fuse_preindex_ldst_1, riscv_fuse_preindex_ld,
  riscv_fuse_preindex_st, riscv_fuse_postindex_ldst_1,
  riscv_fuse_postindex_ld, riscv_fuse_postindex_st,
  riscv_fuse_ldst_pair_1, riscv_fuse_ldst_pair_inc,
  riscv_fuse_ldst_pair_dec, riscv_fuse_fldfst_pair_inc,
  riscv_fuse_fldfst_pair_dec): New function implementing the
  corresponding RISCV_FUSE_* pair.
  (riscv_fusion_table): Add entries for the new pairs.
  * config/riscv/riscv-protos.h (enum riscv_fusion_pairs): Add pair
  flags.
This is getting pretty large and tedious to try and work through from a
review standpoint.  I hate to ask, but can we break this down into
individual cases to aid review?

jeff
Yes, certainly.  I am sorry that this patch made the review harder.  I
had assumed that fewer patches would reduce the overall review work,
but overlooked that putting all the recognizers in one patch makes each
individual case harder to review.

I will split the patch by individual fusion case or closely related
fusion family, and place the necessary common helpers before the
relevant features.  This should make each patch independently
understandable and reviewable.  I apologize again for the extra work.
No need to apologize.  It's often not obvious when to break something 
down or leave it as is.   Thanks for being willing to break it down, I 
do realize it's more work for you, but I suspect we'll be able to move a 
lot of these forward quickly and we may end up iterating on one or two.

Jeff