On Tue, Oct 13, 2026 at 10:27 AM Shreesh Adiga <[email protected]> wrote: > > > > On Mon, Oct 12, 2026 at 2:06 PM Uros Bizjak <[email protected]> wrote: >> >> On Wed, Oct 7, 2026 at 6:32 PM Shreesh Adiga >> <[email protected]> wrote: >> > >> > >> > >> > On Tue, Sep 15, 2026 at 10:03 PM Uros Bizjak <[email protected]> wrote: >> >> >> >> 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. >> >> >> > >> > Hi Andrea, can you help with this hwint.cc changes review part? >> >> A quick chat with AI returned the following solution: >> >> You can avoid touching hwint.cc. crc32q (c, d) == crc32l (crc32l (c, d >> & 0xffffffff), d >> 32), so ix86_fold_builtin can call >> calculate_reversed_crc twice with crc_bits == data_bits == 32. That >> keeps the assertion for the other callers (the middle-end CRC code) >> and removes the need for the middle-end change. >> > > Sure it might work but I'd not want to do extra work making more changes > in x86 and aarch64 :( > I'm rather surprised to see this series is still not merged given that LLVM > merged > my PRs for this exact optimization of const folding crc32 intrinsics for X86, > aarch64 and ARM along with few refactoring changes all within a span of 2 > weeks. > I'm also working on folding "_mm_crc32_u32(x, x) -> 0" for LLVM currently.
Note I have not responded until now since the GNU cauldron was the first weekend in October and I am still recovering from the trip. So partly this got caught during the conference. Sorry about that. I am still trying to understand the assert and why it is there to make sure it can be safely removed. I had wished someone like Jeff would review it since he worked on this code the most. Anyways I should have a good understanding of the code later today and make a good review on it. Thanks, Andrea > > Anyways I am not in a hurry :) so hopefully this can be merged eventually. > > Thanks, > Shreesh > >> >> Uros. >> >> > >> > Thanks, >> > Shreesh >> > >> >> >> >> 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 >> >> >
