On 9/13/24 5:05 AM, Mariam Arutunian wrote:
Add two new internal functions (IFN_CRC, IFN_CRC_REV), to provide faster
CRC generation.
One performs bit-forward and the other bit-reversed CRC computation.
If CRC optabs are supported, they are used for the CRC computation.
Otherwise, table-based CRC is generated.
The supported data and CRC sizes are 8, 16, 32, and 64 bits.
The polynomial is without the leading 1.
A table with 256 elements is used to store precomputed CRCs.
For the reflection of inputs and the output, a simple algorithm involving
SHIFT, AND, and OR operations is used.
gcc/
* doc/md.texi (crc@var{m}@var{n}4,
crc_rev@var{m}@var{n}4): Document.
* expr.cc (calculate_crc): New function.
(assemble_crc_table): Likewise.
(generate_crc_table): Likewise.
(calculate_table_based_CRC): Likewise.
(emit_crc): Likewise.
(expand_crc_table_based): Likewise.
(gen_common_operation_to_reflect): Likewise.
(reflect_64_bit_value): Likewise.
(reflect_32_bit_value): Likewise.
(reflect_16_bit_value): Likewise.
(reflect_8_bit_value): Likewise.
(generate_reflecting_code_standard): Likewise.
(expand_reversed_crc_table_based): Likewise.
* expr.h (generate_reflecting_code_standard): New function declaration.
(expand_crc_table_based): Likewise.
(expand_reversed_crc_table_based): Likewise.
* internal-fn.cc: (crc_direct): Define.
(direct_crc_optab_supported_p): Likewise.
(expand_crc_optab_fn): New function
* internal-fn.def (CRC, CRC_REV): New internal functions.
* optabs.def (crc_optab, crc_rev_optab): New optabs.
Looks pretty good. Just one question/comment:
+void
+emit_crc (machine_mode crc_mode, rtx* crc, rtx* op0)
+{
+ if (GET_MODE_BITSIZE (crc_mode).to_constant () == 32
+ && GET_MODE_BITSIZE (word_mode) == 64)
+ {
+ rtx a_low = gen_lowpart (crc_mode, *crc);
+ *crc = gen_rtx_SIGN_EXTEND (word_mode, a_low);
+ }
+ rtx tgt = *op0;
+ if (word_mode != crc_mode)
+ tgt = simplify_gen_subreg (word_mode, *op0, crc_mode, 0);
+ emit_move_insn (tgt, *crc);
+}
It seems to me that first clause ought to apply any time word mode is
larger than crc mode rather than making it check 32/64 magic constants.
Jeff
