"llvm.x86.pclmulqdq.256 is not yet supported" in crc32fast

This is a strange one, because it only popped up recently on rustc nightly with cranelift.

(To be clear, I am not the developer of his library, just an indirect user of it via flate2.)

The offending line pointed to by the backtrace seems to be here.

rustc 1.100.0-nightly (17fd5b8a3 2026-08-28)

Error with relevant backtrace:

thread 'main' (1056342) panicked at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/core/src/panicking.rs:225:5:
llvm.x86.pclmulqdq.256 is not yet supported.
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/std/src/panicking.rs:676:5
   1: core::panicking::panic_nounwind_fmt::runtime
             at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/core/src/panicking.rs:122:22
   2: core::panicking::panic_nounwind_fmt
             at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/core/src/intrinsics/mod.rs:2641:9
   3: core::panicking::panic_nounwind
             at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/core/src/panicking.rs:225:5
   4: core::core_arch::x86::vpclmulqdq::_mm256_clmulepi64_epi128::<0>
             at /rustc/17fd5b8a37b6667b6cc137f3cc35f09759768a3b/library/core/src/../../stdarch/crates/core_arch/src/x86/vpclmulqdq.rs:60:14
   5: crc32fast::specialized::pclmulqdq::reduce256
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/crc32fast-1.5.1/src/specialized/pclmulqdq.rs:427:14
   6: crc32fast::specialized::pclmulqdq::calculate_avx2
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/crc32fast-1.5.1/src/specialized/pclmulqdq.rs:224:14
   7: crc32fast::specialized::pclmulqdq::calculate_avx512
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/crc32fast-1.5.1/src/specialized/pclmulqdq.rs:261:16
   8: <crc32fast::specialized::pclmulqdq::State>::update
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/crc32fast-1.5.1/src/specialized/pclmulqdq.rs:101:33
   9: <crc32fast::Hasher>::update
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/crc32fast-1.5.1/src/lib.rs:129:50
  10: <flate2::crc::inner::Crc>::update
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/flate2-1.1.10/src/crc.rs:71:13
  11: <flate2::crc::Crc>::update
             at /home/emblemparade/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/flate2-1.1.10/src/crc.rs:31:9
...

Start with the reported call path in crc32fast's src/specialized/pclmulqdq.rs, especially reduce256 at line 427, and the Rust core_arch intrinsic _mm256_clmulepi64_epi128 shown in the backtrace. Reproduce the failure with rustc nightly and Cranelift, then verify that the crc32fast path no longer panics on llvm.x86.pclmulqdq.256.