On Tue, Sep 15, 2026 at 3:54 PM Shreesh Adiga
<[email protected]> wrote:
>
> Add const folding for x86 _mm_crc32_u8/u16/u32/u64 intrinsics.
> Added tests to ensure the values are computed as expected.
>
> gcc/ChangeLog:
>
> * config/i386/i386.cc (ix86_fold_builtin): Add constant folding
> for the SSE4.2 crc32 intrinsics (_mm_crc32_u8/u16/u32/u64) by
> invoking calculate_reversed_crc with the CRC32C polynomial.
> * hwint.cc (calculate_reversed_crc): Relax the crc_bits >=
> data_bits assertion; the shift-register loop still resolves the
> low crc_bits correctly before the upper data_bits reach bit 0,
> so this allows folding _mm_crc32_u64 where crc_bits == 32 and
> data_bits == 64.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/i386/crc32-const-fold.c: New test.
Please follow GNU ChangeLog standards, like:
gcc/ChangeLog:
* config/i386/i386.cc (ix86_fold_builtin) <IX86_BUILTIN_CRC32QI,
IX86_BUILTIN_CRC32HI, IX86_BUILTIN_CRC32SI, IX86_BUILTIN_CRC32DI>:
Add constant folding for the SSE4.2 crc32 intrinsics.
* hwint.cc (calculate_reversed_crc): Remove the crc_bits >=
data_bits assertion.
gcc/testsuite/ChangeLog:
* gcc.target/i386/crc32-const-fold.c: New test.
ChangeLog entry should say *what* is changed, not *why* it is changed.
The explanation itself should go in the commit message.
OK for the x86 part, the hwint.cc needs a middle-end maintainer's review.
Thanks,
Uros.
> Signed-off-by: Shreesh Adiga <[email protected]>
> ---
> gcc/config/i386/i386.cc | 18 ++
> gcc/hwint.cc | 2 +-
> .../gcc.target/i386/crc32-const-fold.c | 154 ++++++++++++++++++
> 3 files changed, 173 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/i386/crc32-const-fold.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index bbb60163a75..79970003cf1 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -19246,6 +19246,24 @@ ix86_fold_builtin (tree fndecl, int n_args,
> }
> break;
>
> + case IX86_BUILTIN_CRC32QI:
> + case IX86_BUILTIN_CRC32HI:
> + case IX86_BUILTIN_CRC32SI:
> + case IX86_BUILTIN_CRC32DI:
> + gcc_assert (n_args == 2);
> + if (tree_fits_uhwi_p (args[0]) && tree_fits_uhwi_p (args[1]))
> + {
> + unsigned HOST_WIDE_INT crc = tree_to_uhwi (args[0]);
> + crc &= 0xffffffff;
> + unsigned HOST_WIDE_INT data = tree_to_uhwi (args[1]);
> + unsigned short data_bits = TYPE_PRECISION (TREE_TYPE (args[1]));
> + unsigned HOST_WIDE_INT res = calculate_reversed_crc (crc, data,
> + 0x1EDC6F41,
> + 32,
> data_bits);
> + return build_int_cstu (TREE_TYPE (TREE_TYPE (fndecl)), res);
> + }
> + break;
> +
> case IX86_BUILTIN_BEXTR32:
> case IX86_BUILTIN_BEXTR64:
> case IX86_BUILTIN_BEXTRI32:
> diff --git a/gcc/hwint.cc b/gcc/hwint.cc
> index 065911d0a77..d89be33f636 100644
> --- a/gcc/hwint.cc
> +++ b/gcc/hwint.cc
> @@ -265,7 +265,7 @@ calculate_reversed_crc (unsigned HOST_WIDE_INT crc,
>
> gcc_checking_assert (crc_bits <= 64);
> gcc_checking_assert (data_bits <= 64);
> - gcc_checking_assert (crc_bits >= data_bits);
> + /* allow data_bits > crc_bits for folding _mm_crc32_u64. */
>
> unsigned HOST_WIDE_INT rev_polynom = reflect_hwi (polynomial, crc_bits);
> crc ^= data;
> diff --git a/gcc/testsuite/gcc.target/i386/crc32-const-fold.c
> b/gcc/testsuite/gcc.target/i386/crc32-const-fold.c
> new file mode 100644
> index 00000000000..92825c4fc1d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/crc32-const-fold.c
> @@ -0,0 +1,154 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mcrc32" } */
> +
> +#include <immintrin.h>
> +
> +unsigned int
> +test_u8_1 ()
> +{
> + return _mm_crc32_u8 (0x02a24bf8, 0xba);
> +}
> +
> +unsigned int
> +test_u8_2 ()
> +{
> + return _mm_crc32_u8 (0x0cd5e10f, 0xe7);
> +}
> +
> +unsigned int
> +test_u8_3 ()
> +{
> + return _mm_crc32_u8 (0x50e739b8, 0x2e);
> +}
> +
> +unsigned int
> +test_u8_4 ()
> +{
> + return _mm_crc32_u8 (0x3c2db116, 0x3d);
> +}
> +
> +unsigned int
> +test_u8_5 ()
> +{
> + return _mm_crc32_u8 (-1, -1);
> +}
> +
> +unsigned int
> +test_u16_1 ()
> +{
> + return _mm_crc32_u16 (0x02a24bf8, 0xd4ba);
> +}
> +
> +unsigned int
> +test_u16_2 ()
> +{
> + return _mm_crc32_u16 (0x0cd5e10f, 0x42e7);
> +}
> +
> +unsigned int
> +test_u16_3 ()
> +{
> + return _mm_crc32_u16 (0x50e739b8, 0x382e);
> +}
> +
> +unsigned int
> +test_u16_4 ()
> +{
> + return _mm_crc32_u16 (0x3c2db116, 0x7f3d);
> +}
> +
> +unsigned int
> +test_u16_5 ()
> +{
> + return _mm_crc32_u16 (-1, -1);
> +}
> +
> +unsigned int
> +test_u32_1 ()
> +{
> + return _mm_crc32_u32 (0x02a24bf8, 0xf37dd4ba);
> +}
> +
> +unsigned int
> +test_u32_2 ()
> +{
> + return _mm_crc32_u32 (0x0cd5e10f, 0x832b42e7);
> +}
> +
> +unsigned int
> +test_u32_3 ()
> +{
> + return _mm_crc32_u32 (0x50e739b8, 0xcefb382e);
> +}
> +
> +unsigned int
> +test_u32_4 ()
> +{
> + return _mm_crc32_u32 (0x3c2db116, 0xd3947f3d);
> +}
> +
> +unsigned int
> +test_u32_5 ()
> +{
> + return _mm_crc32_u32 (-1, -1);
> +}
> +
> +#ifdef __x86_64__
> +unsigned long long
> +test_u64_1 ()
> +{
> + return _mm_crc32_u64 (0x9f65239602a24bf8, 0x894a58bff37dd4ba);
> +}
> +
> +unsigned long long
> +test_u64_2 ()
> +{
> + return _mm_crc32_u64 (0x06ef97970cd5e10f, 0x24334e2e832b42e7);
> +}
> +
> +unsigned long long
> +test_u64_3 ()
> +{
> + return _mm_crc32_u64 (0x5024a45450e739b8, 0x289ee1b7cefb382e);
> +}
> +
> +unsigned long long
> +test_u64_4 ()
> +{
> + return _mm_crc32_u64 (0xcbc89e1c3c2db116, 0xa89143dad3947f3d);
> +}
> +
> +unsigned long long
> +test_u64_5 ()
> +{
> + return _mm_crc32_u64 (-1, -1);
> +}
> +#endif
> +
> +/* Test that there is no crc32 instruction emitted. */
> +/* { dg-final { scan-assembler-not "crc32\[bwlq\]" } } */
> +
> +/* Test the expected values. */
> +/* { dg-final { scan-assembler-times "-1606234368," 1 } } */
> +/* { dg-final { scan-assembler-times "1776624948," 1 } } */
> +/* { dg-final { scan-assembler-times "-1269171002," 1 } } */
> +/* { dg-final { scan-assembler-times "-1190655916," 1 } } */
> +/* { dg-final { scan-assembler-times "16777215," 1 } } */
> +
> +/* { dg-final { scan-assembler-times "350827643," 1 } } */
> +/* { dg-final { scan-assembler-times "1464882880," 1 } } */
> +/* { dg-final { scan-assembler-times "1604487598," 1 } } */
> +/* { dg-final { scan-assembler-times "-1181930003," 1 } } */
> +/* { dg-final { scan-assembler-times "65535," 1 } } */
> +
> +/* { dg-final { scan-assembler-times "2122844148," 1 } } */
> +/* { dg-final { scan-assembler-times "881727033," 1 } } */
> +/* { dg-final { scan-assembler-times "139192539," 1 } } */
> +/* { dg-final { scan-assembler-times "1861871255," 1 } } */
> +/* { dg-final { scan-assembler-times "xorl\[\\t \]+%eax, %eax" 1 } } */
> +
> +/* { dg-final { scan-assembler-times "3230864714" 1 { target { ! ia32 } } }
> } */
> +/* { dg-final { scan-assembler-times "337502055" 1 { target { ! ia32 } } } }
> */
> +/* { dg-final { scan-assembler-times "712052683" 1 { target { ! ia32 } } } }
> */
> +/* { dg-final { scan-assembler-times "1390230251" 1 { target { ! ia32 } } }
> } */
> +/* { dg-final { scan-assembler-times "3080238136" 1 { target { ! ia32 } } }
> } */
> --
> 2.55.0
>
