[PATCH] RISC-V: PR33216, Allow c.slli, c.srai, c.srli with 0 immediate as a hint

[Jan Beulich]

On 29.07.2025 06:45, Nelson Chu wrote:
> The original patch,
> e6f372ba661bb0d8eec1e22a6dc1ad9937336e4d
> 
> Since recently c.slli64, c.srai64, and c.srli64 have been removed from the
> riscv-isa-manual, c.slli, c.srli, and c.srai with 0 immediate are now listed
> as hints,
> https://github.com/riscv/riscv-isa-manual/pull/1942 and https://github.com/riscv/riscv-isa-manual/pull/2093
> 
> So allow c.slli, c.srli, and c.srai with 0 immediate as a hint.  Also allow to
> assemble slli, srli and srai with 0 immediate to hint c.slli, c.srli and c.srai
> when rvc is enabled.  The c.slli64, c.srai64, and c.srli64 should be kept as
> aliases, so dis-assembler should disassemble to c.slli, c.srli, and c.srai with
> 0 immediate.

I don't quite understand the point of retaining ...

> @@ -1199,12 +1174,12 @@ const struct riscv_opcode riscv_opcodes[] =
>  {"c.and",      0, INSN_CLASS_ZCA,   "Cs,Ct",     MATCH_C_AND, MASK_C_AND, match_opcode, 0 },
>  {"c.or",       0, INSN_CLASS_ZCA,   "Cs,Ct",     MATCH_C_OR, MASK_C_OR, match_opcode, 0 },
>  {"c.xor",      0, INSN_CLASS_ZCA,   "Cs,Ct",     MATCH_C_XOR, MASK_C_XOR, match_opcode, 0 },
> -{"c.slli",     0, INSN_CLASS_ZCA,   "d,C>",      MATCH_C_SLLI, MASK_C_SLLI, match_c_slli, 0 },
> -{"c.srli",     0, INSN_CLASS_ZCA,   "Cs,C>",     MATCH_C_SRLI, MASK_C_SRLI, match_c_slli, 0 },
> -{"c.srai",     0, INSN_CLASS_ZCA,   "Cs,C>",     MATCH_C_SRAI, MASK_C_SRAI, match_c_slli, 0 },
> -{"c.slli64",   0, INSN_CLASS_ZCA,   "d",         MATCH_C_SLLI64, MASK_C_SLLI64, match_c_slli64, 0 },
> -{"c.srli64",   0, INSN_CLASS_ZCA,   "Cs",        MATCH_C_SRLI64, MASK_C_SRLI64, match_c_slli64, 0 },
> -{"c.srai64",   0, INSN_CLASS_ZCA,   "Cs",        MATCH_C_SRAI64, MASK_C_SRAI64, match_c_slli64, 0 },
> +{"c.slli64",   0, INSN_CLASS_ZCA,   "d",         MATCH_C_SLLI64, MASK_C_SLLI64, match_c_slli64, INSN_ALIAS },
> +{"c.srli64",   0, INSN_CLASS_ZCA,   "Cs",        MATCH_C_SRLI64, MASK_C_SRLI64, match_c_slli64, INSN_ALIAS },
> +{"c.srai64",   0, INSN_CLASS_ZCA,   "Cs",        MATCH_C_SRAI64, MASK_C_SRAI64, match_c_slli64, INSN_ALIAS },

... these three. The assembler should reject them now, shouldn't it? And the
disassembler will never use them: If use of aliases is enabled, the earlier
entries which aren't c. prefixed would be used, whereas is aliases are
disabled, ...

> +{"c.slli",     0, INSN_CLASS_ZCA,   "d,C>",      MATCH_C_SLLI, MASK_C_SLLI, match_opcode, 0 },
> +{"c.srli",     0, INSN_CLASS_ZCA,   "Cs,C>",     MATCH_C_SRLI, MASK_C_SRLI, match_opcode, 0 },
> +{"c.srai",     0, INSN_CLASS_ZCA,   "Cs,C>",     MATCH_C_SRAI, MASK_C_SRAI, match_opcode, 0 },

... these three would be used.

Jan