Re: [RFC/RFA] [PATCH 02/12] Add built-ins and tests for bit-forward and bit-reversed CRCs

[Richard Biener <richard.guenther@gmail.com>]

On Fri, May 24, 2024 at 10:44 AM Mariam Arutunian
<mariamarutunian@gmail.com> wrote:
>
> This patch introduces new built-in functions to GCC for computing bit-forward and bit-reversed CRCs.
> These builtins aim to provide efficient CRC calculation capabilities.
> When the target architecture supports CRC operations (as indicated by the presence of a CRC optab),
> the builtins will utilize the expander to generate CRC code.
> In the absence of hardware support, the builtins default to generating code for a table-based CRC calculation.

I wonder whether for embedded target use we should arrange for the
table-based CRC calculation
to be out-of-line and implemented in a way so uses across TUs can be
merged?  I guess a generic implementation
inside libgcc is difficult?

>
> The builtins are defined as follows:
> __builtin_rev_crc16_data8,
> __builtin_rev_crc32_data8, __builtin_rev_crc32_data16, __builtin_rev_crc32_data32
> __builtin_crc8_data8,
> __builtin_crc16_data16, __builtin_crc16_data8,
> __builtin_crc32_data8, __builtin_crc32_data16, __builtin_crc32_data32,
> __builtin_crc64_data8, __builtin_crc64_data16,  __builtin_crc64_data32, __builtin_crc64_data64
>
> Each builtin takes three parameters:
> crc: The initial CRC value.
> data: The data to be processed.
> polynomial: The CRC polynomial without the leading 1.
>
> To validate the correctness of these builtins, this patch also includes additions to the GCC testsuite.
> This enhancement allows GCC to offer developers high-performance CRC computation options
> that automatically adapt to the capabilities of the target hardware.
>
> Co-authored-by: Joern Rennecke <joern.rennecke@embecosm.com>
>
> Not complete. May continue the work if these built-ins are needed.
>
> gcc/
>
>  * builtin-types.def (BT_FN_UINT8_UINT8_UINT8_CONST_SIZE): Define.
>  (BT_FN_UINT16_UINT16_UINT8_CONST_SIZE): Likewise.
>           (BT_FN_UINT16_UINT16_UINT16_CONST_SIZE): Likewise.
>           (BT_FN_UINT32_UINT32_UINT8_CONST_SIZE): Likewise.
>           (BT_FN_UINT32_UINT32_UINT16_CONST_SIZE): Likewise.
>           (BT_FN_UINT32_UINT32_UINT32_CONST_SIZE): Likewise.
>           (BT_FN_UINT64_UINT64_UINT8_CONST_SIZE): Likewise.
>           (BT_FN_UINT64_UINT64_UINT16_CONST_SIZE): Likewise.
>           (BT_FN_UINT64_UINT64_UINT32_CONST_SIZE): Likewise.
>           (BT_FN_UINT64_UINT64_UINT64_CONST_SIZE): Likewise.
>           * builtins.cc (associated_internal_fn): Handle BUILT_IN_CRC8_DATA8,
>           BUILT_IN_CRC16_DATA8, BUILT_IN_CRC16_DATA16,
>           BUILT_IN_CRC32_DATA8, BUILT_IN_CRC32_DATA16, BUILT_IN_CRC32_DATA32,
>           BUILT_IN_CRC64_DATA8, BUILT_IN_CRC64_DATA16, BUILT_IN_CRC64_DATA32,
>           BUILT_IN_CRC64_DATA64,
>           BUILT_IN_REV_CRC8_DATA8,
>           BUILT_IN_REV_CRC16_DATA8, BUILT_IN_REV_CRC16_DATA16,
>           BUILT_IN_REV_CRC32_DATA8, BUILT_IN_REV_CRC32_DATA16, BUILT_IN_REV_CRC32_DATA32.
>           (expand_builtin_crc_table_based): New function.
>           (expand_builtin): Handle BUILT_IN_CRC8_DATA8,
>           BUILT_IN_CRC16_DATA8, BUILT_IN_CRC16_DATA16,
>           BUILT_IN_CRC32_DATA8, BUILT_IN_CRC32_DATA16, BUILT_IN_CRC32_DATA32,
>           BUILT_IN_CRC64_DATA8, BUILT_IN_CRC64_DATA16, BUILT_IN_CRC64_DATA32,
>           BUILT_IN_CRC64_DATA64,
>           BUILT_IN_REV_CRC8_DATA8,
>           BUILT_IN_REV_CRC16_DATA8, BUILT_IN_REV_CRC16_DATA16,
>           BUILT_IN_REV_CRC32_DATA8, BUILT_IN_REV_CRC32_DATA16, BUILT_IN_REV_CRC32_DATA32.
>           * builtins.def (BUILT_IN_CRC8_DATA8): New builtin.
>           (BUILT_IN_CRC16_DATA8): Likewise.
>           (BUILT_IN_CRC16_DATA16): Likewise.
>           (BUILT_IN_CRC32_DATA8): Likewise.
>           (BUILT_IN_CRC32_DATA16): Likewise.
>           (BUILT_IN_CRC32_DATA32): Likewise.
>           (BUILT_IN_CRC64_DATA8): Likewise.
>           (BUILT_IN_CRC64_DATA16): Likewise.
>           (BUILT_IN_CRC64_DATA32): Likewise.
>           (BUILT_IN_CRC64_DATA64): Likewise.
>           (BUILT_IN_REV_CRC8_DATA8): New builtin.
>           (BUILT_IN_REV_CRC16_DATA8): Likewise.
>           (BUILT_IN_REV_CRC16_DATA16): Likewise.
>           (BUILT_IN_REV_CRC32_DATA8): Likewise.
>           (BUILT_IN_REV_CRC32_DATA16): Likewise.
>           (BUILT_IN_REV_CRC32_DATA32): Likewise.
>           * builtins.h (expand_builtin_crc_table_based): New function declaration.
>           * doc/extend.texti (__builtin_rev_crc16_data8,
>           (__builtin_rev_crc32_data32, __builtin_rev_crc32_data8,
>           __builtin_rev_crc32_data16, __builtin_crc8_data8,
>           __builtin_crc16_data16, __builtin_crc16_data8,
>           __builtin_crc32_data32, __builtin_crc32_data8,
>           __builtin_crc32_data16, __builtin_crc64_data64,
>           __builtin_crc64_data8, __builtin_crc64_data16,
>           __builtin_crc64_data32): Document.
>
>       gcc/testsuite/
>
>          * gcc.c-torture/compile/crc-builtin-rev-target32.c
>          * gcc.c-torture/compile/crc-builtin-rev-target64.c
>          * gcc.c-torture/compile/crc-builtin-target32.c
>          * gcc.c-torture/compile/crc-builtin-target64.c
>
> Signed-off-by: Mariam Arutunian <mariamarutunian@gmail.com>