On 10/25/19 11:39 AM, Craig Blackmore wrote: > This patch aims to allow more load/store instructions to be compressed by > replacing a load/store of 'base register + large offset' with a new load/store > of 'new base + small offset'. If the new base gets stored in a compressed > register, then the new load/store can be compressed. Since there is an > overhead > in creating the new base, this change is only attempted when 'base register' > is > referenced in at least 4 load/stores in a basic block. > > The optimization is implemented in a new RISC-V specific pass called > shorten_memrefs which is enabled for RVC targets. It has been developed for > the > 32-bit lw/sw instructions but could also be extended to 64-bit ld/sd in > future. > > Tested on bare metal rv32i, rv32iac, rv32im, rv32imac, rv32imafc, rv64imac, > rv64imafdc via QEMU. No regressions. > > gcc/ChangeLog: > > * config.gcc: Add riscv-shorten-memrefs.o to extra_objs for riscv. > * config/riscv/riscv-passes.def: New file. > * config/riscv/riscv-protos.h (make_pass_shorten_memrefs): Declare. > * config/riscv/riscv-shorten-memrefs.c: New file. > * config/riscv/riscv.c (tree-pass.h): New include. > (riscv_compressed_reg_p): New Function > (riscv_compressed_lw_offset_p): Likewise. > (riscv_compressed_lw_address_p): Likewise. > (riscv_shorten_lw_offset): Likewise. > (riscv_legitimize_address): Attempt to convert base + large_offset > to compressible new_base + small_offset. > (riscv_address_cost): Make anticipated compressed load/stores > cheaper for code size than uncompressed load/stores. > (riscv_register_priority): Move compressed register check to > riscv_compressed_reg_p. > * config/riscv/riscv.h (RISCV_MAX_COMPRESSED_LW_OFFSET): Define. > * config/riscv/riscv.opt (mshorten-memefs): New option. > * config/riscv/t-riscv (riscv-shorten-memrefs.o): New rule. > (PASSES_EXTRA): Add riscv-passes.def. > * doc/invoke.texi: Document -mshorten-memrefs. This has traditionally been done via the the legitimize_address hook. Is there some reason that hook is insufficient for this case?
The hook, IIRC, is called out explow.c. Jeff
