itsscb/rust
1
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-10-05 03:36:21 +00:00
Code Issues Packages Projects Releases Wiki Activity
rust/library/core/src/lib.rs
Dylan DPC 8ed3a80b9a
Rollup merge of #103287 - saethlin:faster-len-check, r=thomcc 
Use a faster allocation size check in slice::from_raw_parts

I've been perusing through the codegen changes that result from turning on the standard library debug assertions. The previous check in here uses saturating arithmetic, which in my experience sometimes makes LLVM just fail to optimize things around the saturating operation.

Here is a demo of the codegen difference: https://godbolt.org/z/WMEqrjajW
Before:
```asm
example::len_check_old:
        mov     rax, rdi
        mov     ecx, 3
        mul     rcx
        setno   cl
        test    rax, rax
        setns   al
        and     al, cl
        ret

example::len_check_old:
        mov     rax, rdi
        mov     ecx, 8
        mul     rcx
        setno   cl
        test    rax, rax
        setns   al
        and     al, cl
        ret
```
After:
```asm
example::len_check_new:
        movabs  rax, 3074457345618258603
        cmp     rdi, rax
        setb    al
        ret

example::len_check_new:
        shr     rdi, 60
        sete    al
        ret
```

Running rustc-perf locally, this looks like up to a 4.5% improvement when `debug-assertions-std = true`.

Thanks ```@LegionMammal978``` (I think that's you?) for turning my idea into a much cleaner implementation.

r? ```@thomcc```
2022-10-26 11:29:53 +05:30

442 lines
14 KiB
Rust
Raw Blame History

//! # The Rust Core Library
//!
//! The Rust Core Library is the dependency-free[^free] foundation of [The
//! Rust Standard Library](../std/index.html). It is the portable glue
//! between the language and its libraries, defining the intrinsic and
//! primitive building blocks of all Rust code. It links to no
//! upstream libraries, no system libraries, and no libc.
//!
//! [^free]: Strictly speaking, there are some symbols which are needed but
//! they aren't always necessary.
//!
//! The core library is *minimal*: it isn't even aware of heap allocation,
//! nor does it provide concurrency or I/O. These things require
//! platform integration, and this library is platform-agnostic.
//!
//! # How to use the core library
//!
//! Please note that all of these details are currently not considered stable.
//!
// FIXME: Fill me in with more detail when the interface settles
//! This library is built on the assumption of a few existing symbols:
//!
//! * `memcpy`, `memcmp`, `memset`, `strlen` - These are core memory routines which are
//! often generated by LLVM. Additionally, this library can make explicit
//! calls to these functions. Their signatures are the same as found in C.
//! These functions are often provided by the system libc, but can also be
//! provided by the [compiler-builtins crate](https://crates.io/crates/compiler_builtins).
//!
//! * `rust_begin_panic` - This function takes four arguments, a
//! `fmt::Arguments`, a `&'static str`, and two `u32`'s. These four arguments
//! dictate the panic message, the file at which panic was invoked, and the
//! line and column inside the file. It is up to consumers of this core
//! library to define this panic function; it is only required to never
//! return. This requires a `lang` attribute named `panic_impl`.
//!
//! * `rust_eh_personality` - is used by the failure mechanisms of the
//! compiler. This is often mapped to GCC's personality function, but crates
//! which do not trigger a panic can be assured that this function is never
//! called. The `lang` attribute is called `eh_personality`.
// Since libcore defines many fundamental lang items, all tests live in a
// separate crate, libcoretest, to avoid bizarre issues.
//
// Here we explicitly #[cfg]-out this whole crate when testing. If we don't do
// this, both the generated test artifact and the linked libtest (which
// transitively includes libcore) will both define the same set of lang items,
// and this will cause the E0152 "found duplicate lang item" error. See
// discussion in #50466 for details.
//
// This cfg won't affect doc tests.
#![cfg(not(test))]
// To run libcore tests without x.py without ending up with two copies of libcore, Miri needs to be
// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
// rustc itself never sets the feature, so this line has no affect there.
#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
#![stable(feature = "core", since = "1.6.0")]
#![doc(
html_playground_url = "https://play.rust-lang.org/",
issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
test(no_crate_inject, attr(deny(warnings))),
test(attr(allow(dead_code, deprecated, unused_variables, unused_mut)))
)]
#![doc(cfg_hide(
not(test),
any(not(feature = "miri-test-libstd"), test, doctest),
no_fp_fmt_parse,
target_pointer_width = "16",
target_pointer_width = "32",
target_pointer_width = "64",
target_has_atomic = "8",
target_has_atomic = "16",
target_has_atomic = "32",
target_has_atomic = "64",
target_has_atomic = "ptr",
target_has_atomic_equal_alignment = "8",
target_has_atomic_equal_alignment = "16",
target_has_atomic_equal_alignment = "32",
target_has_atomic_equal_alignment = "64",
target_has_atomic_equal_alignment = "ptr",
target_has_atomic_load_store = "8",
target_has_atomic_load_store = "16",
target_has_atomic_load_store = "32",
target_has_atomic_load_store = "64",
target_has_atomic_load_store = "ptr",
))]
#![no_core]
#![rustc_coherence_is_core]
//
// Lints:
#![deny(rust_2021_incompatible_or_patterns)]
#![deny(unsafe_op_in_unsafe_fn)]
#![warn(deprecated_in_future)]
#![warn(missing_debug_implementations)]
#![warn(missing_docs)]
#![allow(explicit_outlives_requirements)]
#![allow(incomplete_features)]
//
// Library features:
#![feature(const_align_offset)]
#![feature(const_align_of_val)]
#![feature(const_arguments_as_str)]
#![feature(const_array_into_iter_constructors)]
#![feature(const_bigint_helper_methods)]
#![feature(const_black_box)]
#![feature(const_caller_location)]
#![feature(const_cell_into_inner)]
#![feature(const_char_convert)]
#![feature(const_clone)]
#![feature(const_cmp)]
#![feature(const_discriminant)]
#![feature(const_eval_select)]
#![feature(const_float_bits_conv)]
#![feature(const_float_classify)]
#![feature(const_fmt_arguments_new)]
#![feature(const_heap)]
#![feature(const_convert)]
#![feature(const_index_range_slice_index)]
#![feature(const_inherent_unchecked_arith)]
#![feature(const_int_unchecked_arith)]
#![feature(const_intrinsic_forget)]
#![feature(const_likely)]
#![feature(const_maybe_uninit_uninit_array)]
#![feature(const_maybe_uninit_as_mut_ptr)]
#![feature(const_maybe_uninit_assume_init)]
#![feature(const_nonnull_new)]
#![feature(const_num_from_num)]
#![feature(const_ops)]
#![feature(const_option)]
#![feature(const_option_ext)]
#![feature(const_pin)]
#![feature(const_ptr_sub_ptr)]
#![feature(const_replace)]
#![feature(const_ptr_as_ref)]
#![feature(const_ptr_is_null)]
#![feature(const_ptr_read)]
#![feature(const_ptr_write)]
#![feature(const_raw_ptr_comparison)]
#![feature(const_size_of_val)]
#![feature(const_slice_from_raw_parts_mut)]
#![feature(const_slice_ptr_len)]
#![feature(const_slice_split_at_mut)]
#![feature(const_str_from_utf8_unchecked_mut)]
#![feature(const_swap)]
#![feature(const_trait_impl)]
#![feature(const_try)]
#![feature(const_type_id)]
#![feature(const_type_name)]
#![feature(const_default_impls)]
#![feature(const_unicode_case_lookup)]
#![feature(const_unsafecell_get_mut)]
#![feature(const_waker)]
#![feature(core_panic)]
#![feature(duration_consts_float)]
#![feature(maybe_uninit_uninit_array)]
#![feature(ptr_alignment_type)]
#![feature(ptr_metadata)]
#![feature(slice_ptr_get)]
#![feature(slice_split_at_unchecked)]
#![feature(str_internals)]
#![feature(utf16_extra)]
#![feature(utf16_extra_const)]
#![feature(variant_count)]
#![feature(const_array_from_ref)]
#![feature(const_slice_from_ref)]
#![feature(const_slice_index)]
#![feature(const_is_char_boundary)]
#![feature(const_cstr_methods)]
#![feature(is_ascii_octdigit)]
//
// Language features:
#![feature(abi_unadjusted)]
#![feature(adt_const_params)]
#![feature(allow_internal_unsafe)]
#![feature(allow_internal_unstable)]
#![feature(associated_type_bounds)]
#![feature(auto_traits)]
#![feature(c_unwind)]
#![feature(cfg_sanitize)]
#![feature(cfg_target_has_atomic)]
#![feature(cfg_target_has_atomic_equal_alignment)]
#![feature(const_fn_floating_point_arithmetic)]
#![feature(const_mut_refs)]
#![feature(const_precise_live_drops)]
#![feature(const_refs_to_cell)]
#![feature(decl_macro)]
#![feature(deprecated_suggestion)]
#![feature(doc_cfg)]
#![feature(doc_notable_trait)]
#![feature(rustdoc_internals)]
#![feature(exhaustive_patterns)]
#![feature(doc_cfg_hide)]
#![feature(extern_types)]
#![feature(fundamental)]
#![feature(if_let_guard)]
#![feature(inline_const)]
#![feature(intra_doc_pointers)]
#![feature(intrinsics)]
#![feature(lang_items)]
#![feature(link_llvm_intrinsics)]
#![feature(macro_metavar_expr)]
#![feature(min_specialization)]
#![feature(must_not_suspend)]
#![feature(negative_impls)]
#![feature(never_type)]
#![feature(no_core)]
#![feature(no_coverage)] // rust-lang/rust#84605
#![feature(platform_intrinsics)]
#![feature(prelude_import)]
#![feature(repr_simd)]
#![feature(rustc_allow_const_fn_unstable)]
#![feature(rustc_attrs)]
#![feature(simd_ffi)]
#![feature(staged_api)]
#![feature(stmt_expr_attributes)]
#![feature(target_feature_11)]
#![feature(trait_alias)]
#![feature(transparent_unions)]
#![feature(try_blocks)]
#![feature(unboxed_closures)]
#![feature(unsized_fn_params)]
#![feature(asm_const)]
#![feature(const_transmute_copy)]
//
// Target features:
#![feature(arm_target_feature)]
#![feature(avx512_target_feature)]
#![feature(cmpxchg16b_target_feature)]
#![feature(f16c_target_feature)]
#![feature(hexagon_target_feature)]
#![feature(mips_target_feature)]
#![feature(powerpc_target_feature)]
#![feature(riscv_target_feature)]
#![feature(rtm_target_feature)]
#![feature(sse4a_target_feature)]
#![feature(tbm_target_feature)]
#![feature(wasm_target_feature)]
// allow using `core::` in intra-doc links
#[allow(unused_extern_crates)]
extern crate self as core;
#[prelude_import]
#[allow(unused)]
use prelude::v1::*;
#[cfg(not(test))] // See #65860
#[macro_use]
mod macros;
// We don't export this through #[macro_export] for now, to avoid breakage.
// See https://github.com/rust-lang/rust/issues/82913
#[cfg(not(test))]
#[unstable(feature = "assert_matches", issue = "82775")]
/// Unstable module containing the unstable `assert_matches` macro.
pub mod assert_matches {
#[unstable(feature = "assert_matches", issue = "82775")]
pub use crate::macros::{assert_matches, debug_assert_matches};
}
#[macro_use]
mod internal_macros;
#[path = "num/shells/int_macros.rs"]
#[macro_use]
mod int_macros;
#[path = "num/shells/i128.rs"]
pub mod i128;
#[path = "num/shells/i16.rs"]
pub mod i16;
#[path = "num/shells/i32.rs"]
pub mod i32;
#[path = "num/shells/i64.rs"]
pub mod i64;
#[path = "num/shells/i8.rs"]
pub mod i8;
#[path = "num/shells/isize.rs"]
pub mod isize;
#[path = "num/shells/u128.rs"]
pub mod u128;
#[path = "num/shells/u16.rs"]
pub mod u16;
#[path = "num/shells/u32.rs"]
pub mod u32;
#[path = "num/shells/u64.rs"]
pub mod u64;
#[path = "num/shells/u8.rs"]
pub mod u8;
#[path = "num/shells/usize.rs"]
pub mod usize;
#[path = "num/f32.rs"]
pub mod f32;
#[path = "num/f64.rs"]
pub mod f64;
#[macro_use]
pub mod num;
/* The libcore prelude, not as all-encompassing as the libstd prelude */
pub mod prelude;
/* Core modules for ownership management */
pub mod hint;
pub mod intrinsics;
pub mod mem;
pub mod ptr;
/* Core language traits */
pub mod borrow;
pub mod clone;
pub mod cmp;
pub mod convert;
pub mod default;
pub mod error;
pub mod marker;
pub mod ops;
/* Core types and methods on primitives */
pub mod any;
pub mod array;
pub mod ascii;
pub mod asserting;
#[unstable(feature = "async_iterator", issue = "79024")]
pub mod async_iter;
pub mod cell;
pub mod char;
pub mod ffi;
pub mod iter;
pub mod option;
pub mod panic;
pub mod panicking;
pub mod pin;
pub mod result;
pub mod sync;
pub mod fmt;
pub mod hash;
pub mod slice;
pub mod str;
pub mod time;
pub mod unicode;
/* Async */
pub mod future;
pub mod task;
/* Heap memory allocator trait */
#[allow(missing_docs)]
pub mod alloc;
// note: does not need to be public
mod bool;
mod tuple;
mod unit;
mod const_closure;
#[stable(feature = "core_primitive", since = "1.43.0")]
pub mod primitive;
// Pull in the `core_arch` crate directly into libcore. The contents of
// `core_arch` are in a different repository: rust-lang/stdarch.
//
// `core_arch` depends on libcore, but the contents of this module are
// set up in such a way that directly pulling it here works such that the
// crate uses the this crate as its libcore.
#[path = "../../stdarch/crates/core_arch/src/mod.rs"]
#[allow(
missing_docs,
missing_debug_implementations,
dead_code,
unused_imports,
unsafe_op_in_unsafe_fn
)]
#[allow(rustdoc::bare_urls)]
// FIXME: This annotation should be moved into rust-lang/stdarch after clashing_extern_declarations is
// merged. It currently cannot because bootstrap fails as the lint hasn't been defined yet.
#[allow(clashing_extern_declarations)]
#[unstable(feature = "stdsimd", issue = "48556")]
mod core_arch;
#[doc = include_str!("../../stdarch/crates/core_arch/src/core_arch_docs.md")]
#[stable(feature = "simd_arch", since = "1.27.0")]
pub mod arch {
#[stable(feature = "simd_arch", since = "1.27.0")]
pub use crate::core_arch::arch::*;
/// Inline assembly.
///
/// Refer to [rust by example] for a usage guide and the [reference] for
/// detailed information about the syntax and available options.
///
/// [rust by example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html
/// [reference]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html
#[stable(feature = "asm", since = "1.59.0")]
#[rustc_builtin_macro]
pub macro asm("assembly template", $(operands,)* $(options($(option),*))?) {
/* compiler built-in */
}
/// Module-level inline assembly.
///
/// Refer to [rust by example] for a usage guide and the [reference] for
/// detailed information about the syntax and available options.
///
/// [rust by example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html
/// [reference]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html
#[stable(feature = "global_asm", since = "1.59.0")]
#[rustc_builtin_macro]
pub macro global_asm("assembly template", $(operands,)* $(options($(option),*))?) {
/* compiler built-in */
}
}
// Pull in the `core_simd` crate directly into libcore. The contents of
// `core_simd` are in a different repository: rust-lang/portable-simd.
//
// `core_simd` depends on libcore, but the contents of this module are
// set up in such a way that directly pulling it here works such that the
// crate uses this crate as its libcore.
#[path = "../../portable-simd/crates/core_simd/src/mod.rs"]
#[allow(missing_debug_implementations, dead_code, unsafe_op_in_unsafe_fn, unused_unsafe)]
#[allow(rustdoc::bare_urls)]
#[unstable(feature = "portable_simd", issue = "86656")]
mod core_simd;
#[doc = include_str!("../../portable-simd/crates/core_simd/src/core_simd_docs.md")]
#[unstable(feature = "portable_simd", issue = "86656")]
pub mod simd {
#[unstable(feature = "portable_simd", issue = "86656")]
pub use crate::core_simd::simd::*;
}
include!("primitive_docs.rs");
Reference in New Issue View Git Blame Copy Permalink