On Mon, Apr 28, 2025 at 8:57 PM H.J. Lu <hjl.to...@gmail.com> wrote: > > On x86, both stores with 32-bit immediate and register are supported: > > 0: 48 c7 40 10 00 00 00 00 movq $0x0,0x10(%rax) > 8: 48 89 50 10 movq %rdx,0x10(%rax) > > But store with 32-bit immediate is 4 byte longer. > > Add UNSPEC_STORE_BY_PIECES to x86 backend for register store to avoid > store with 32-bit immediate for shorter encoding and add a target hook to > select the store instruction used by the store by_pieces infrastructure > so that a target can choose a specific instruction for shorter encoding. > When optimizing on x86, we choose register store: > > 1. If length-changing prefix (LCP) stall is avoided with 16-bit register > store. Or > 2. If more than 2 stores with 32-bit immediate will be used. > > gcc/ > > * expr.c (store_by_pieces_d::prepare_mode): Call > targetm.store_by_pieces_icode to get store by_pieces insn code. > * target.def (store_by_pieces_icode): New hook. > * targhooks.cc (default_store_by_pieces_icode): New. > targhooks.h (default_store_by_pieces_icode): Likewise. > * config/i386/i386.cc (ix86_store_by_pieces_icode): New. > (TARGET_STORE_BY_PIECES_ICODE): Likewise. > * config/i386/i386.md (UNSPEC_STORE_BY_PIECES): New. > (store_by_pieces_mov<mode>): Likewise. > (store_by_pieces_mov<mode>_1): Likewise. > * config/i386/x86-tune.def (X86_TUNE_USE_REGISTER_STORE_BY_PIECES): > Likewise. > * doc/tm.texi: Regenerated. > * doc/tm.texi.in: Add TARGET_STORE_BY_PIECES_ICODE. > > gcc/testsuite/ > > * gcc.target/i386/memset-strategy-10.c: New test. > * gcc.target/i386/memset-strategy-11.c: Likewise. > * gcc.target/i386/memset-strategy-12.c: Likewise. > * gcc.target/i386/memset-strategy-13.c: Likewise. > * gcc.target/i386/memset-strategy-14.c: Likewise. > * gcc.target/i386/memset-strategy-15.c: Likewise. > * gcc.target/i386/memset-strategy-16.c: Likewise. > * gcc.target/i386/memset-strategy-17.c: Likewise. > * gcc.target/i386/memset-strategy-18.c: Likewise. > * gcc.target/i386/memset-strategy-19.c: Likewise. > * gcc.target/i386/memset-strategy-20.c: Likewise. > * gcc.target/i386/memset-strategy-21.c: Likewise. > * gcc.target/i386/pr72839.c: Scan for register store. > > OK for master? > > Thanks. > > -- > H.J.
PING: https://gcc.gnu.org/pipermail/gcc-patches/2025-April/682007.html -- H.J.
