rustc-LLVM ERROR: Cannot select: 0x11c366ee0: i32 = Constant<4096>

[astolarz]

The compiler doesn't like the use of the number 4096 in the piper crate. POC repo (more info in readme).

Code

pub fn write_buf(&mut self, max: usize) -> &mut [u8] {
        let n = max
            .min(self.zeroed_until * 2 + 4096) // Don't zero too many bytes when starting.
            .min(self.available_space()) // No more than space in the pipe.
            .min(self.inner.cap - self.inner.real_index(self.tail)); // Don't go past the buffer boundary.

Meta

rustc --version --verbose:

rustc 1.93.0-nightly (2b43689c5 2026-01-27) (1.93.0.0)
binary: rustc
commit-hash: 2b43689c53a55786249fe1d7263826eef2d74725
commit-date: 2026-01-27
host: aarch64-apple-darwin
release: 1.93.0-nightly
LLVM version: 20.1.1

Error output

rustc-LLVM ERROR: Cannot select: 0x11c366ee0: i32 = Constant<4096>
In function: _RNvMs7_CshefiTHCmSNc_5piperNtB5_6Writer9write_buf
error: could not compile `piper` (lib)

Backtrace

RUST_BACKTRACE=1 cargo build
   Compiling serde v1.0.228
   Compiling esp-idf-hal v0.46.2
   Compiling piper-cannot-select v0.1.0 (/Users/aaron/projects/rust/piper-cannot-select)
   Compiling piper v0.2.5
rustc-LLVM ERROR: Cannot select: 0x10aff6ee0: i32 = Constant<4096>
In function: _RNvMs7_CshefiTHCmSNc_5piperNtB5_6Writer9write_buf
error: could not compile `piper` (lib)

Caused by:
  process didn't exit successfully: `/Users/aaron/.rustup/toolchains/esp/bin/rustc --crate-name piper --edition=2018 /Users/aaron/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/piper-0.2.5/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=184 --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C debuginfo=2 -C debug-assertions=on --cfg 'feature="default"' --cfg 'feature="futures-io"' --cfg 'feature="std"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("default", "futures-io", "portable-atomic", "portable-atomic-util", "portable_atomic_crate", "std"))' -C metadata=ed420a438d4806d5 -C extra-filename=-0aeb95c8411ed1f8 --out-dir /Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps --target xtensa-esp32s3-espidf -C linker=ldproxy -L dependency=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps -L dependency=/Users/aaron/projects/rust/piper-cannot-select/target/debug/deps --extern 'noprelude:alloc=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/liballoc-30e5baa4b6d00e18.rmeta' --extern atomic_waker=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libatomic_waker-0fd68d7b767eec94.rmeta --extern 'noprelude:compiler_builtins=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libcompiler_builtins-47e625284373be4e.rmeta' --extern 'noprelude:core=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libcore-f59693a0f77c4fec.rmeta' --extern fastrand=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libfastrand-3fc7d4fc0af80850.rmeta --extern futures_io=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libfutures_io-84b9581e4e6da00a.rmeta --extern 'noprelude:panic_abort=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libpanic_abort-d4698a26ec923e56.rmeta' --extern 'noprelude:panic_unwind=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libpanic_unwind-ef249d08ea8e9b31.rmeta' --extern 'noprelude:proc_macro=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libproc_macro-17219ea72554725c.rmeta' --extern 'noprelude:std=/Users/aaron/projects/rust/piper-cannot-select/target/xtensa-esp32s3-espidf/debug/deps/libstd-0f3b1fc360180af2.rmeta' -Z unstable-options --cap-lints allow` (exit status: 101)
warning: build failed, waiting for other jobs to finish...