It's simple enough, so LGTM for trunk :)
Fei Gao 於 2024年4月15日 週一 14:38 寫道：
> When one of the two input operands is 0, ADD and IOR are functionally
> equivalent.
> ADD is slightly preferred over IOR because ADD has a higher likelihood
> of being implemented as a compressed instruction when compared to IOR.
> C.ADD uses the CR format with any of the 32 RVI registers availble,
> while C.OR uses the CA format with limit to just 8 of them.
>
> Conditional select, if zero case:
> rd = (rc == 0) ? rs1 : rs2
>
> before patch:
>
> czero.nez rd, rs1, rc
> czero.eqz rtmp, rs2, rc
> or rd, rd, rtmp
>
> after patch:
>
> czero.eqz rd, rs1, rc
> czero.nez rtmp, rs2, rc
> add rd, rd, rtmp
>
> Same trick applies for the conditional select, if non-zero case:
> rd = (rc != 0) ? rs1 : rs2
>
> riscv-gnu-toolchain regression tests have been passed with no new failure.
> ---
> gcc/config/riscv/riscv.cc| 2 +-
> .../gcc.target/riscv/zicond-prefer-add-to-or.c | 16
> 2 files changed, 17 insertions(+), 1 deletion(-)
> create mode 100644
> gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index e5f00806bb9..93c736549c9 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -4709,7 +4709,7 @@ riscv_expand_conditional_move (rtx dest, rtx op, rtx
> cons, rtx alt)
> gen_rtx_IF_THEN_ELSE (mode, cond1,
> CONST0_RTX (mode),
> alt)));
> - riscv_emit_binary (IOR, dest, reg1, reg2);
> + riscv_emit_binary (PLUS, dest, reg1, reg2);
> return true;
> }
> }
> diff --git a/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> new file mode 100644
> index 000..f3f7beb0b5e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gc_zicond -mabi=lp64d -mbranch-cost=4" {
> target { rv64 } } } */
> +/* { dg-options "-march=rv32gc_zicond -mabi=ilp32f -mbranch-cost=4" {
> target { rv32 } } } */
> +/* { dg-skip-if "" { *-*-* } {"-O0" "-Og" "-Os" "-Oz"} } */
> +
> +long cond_select_if_zero(long a, long b, long c) {
> + return a == 0 ? c : b;
> +}
> +
> +long cond_select_if_non_zero(long a, long b, long c) {
> + return a != 0 ? c : b;
> +}
> +
> +/* { dg-final { scan-assembler-times {add\t} 2 } } */
> +/* { dg-final { scan-assembler-not {or\t} } } */
> +
> --
> 2.17.1
>
>
