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Add different misaligned path for archs with unaligned support

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This commit is contained in:
Gary Guo 2021-08-21 03:45:38 +01:00
parent 8535675a17
commit 709bd6e11c
2 changed files with 43 additions and 0 deletions
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5
library/compiler-builtins/build.rs
View file

@ -33,6 +33,11 @@ fn main() {
println!("cargo:rustc-cfg=feature=\"mem\"");
}
// These targets have hardware unaligned access support.
if target.contains("x86_64") || target.contains("i686") || target.contains("aarch64") {
println!("cargo:rustc-cfg=feature=\"mem-unaligned\"");
}
// NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
// target triple. This is usually correct for our built-in targets but can break in presence of
// custom targets, which can have arbitrary names.

38
library/compiler-builtins/src/mem/impls.rs
View file

@ -16,6 +16,14 @@ const WORD_COPY_THRESHOLD: usize = if 2 * WORD_SIZE > 16 {
16
};
#[cfg(feature = "mem-unaligned")]
unsafe fn read_usize_unaligned(x: *const usize) -> usize {
// Do not use `core::ptr::read_unaligned` here, since it calls `copy_nonoverlapping` which
// is translated to memcpy in LLVM.
let x_read = (x as *const [u8; core::mem::size_of::<usize>()]).read();
core::mem::transmute(x_read)
}
#[inline(always)]
pub unsafe fn copy_forward(mut dest: *mut u8, mut src: *const u8, mut n: usize) {
#[inline(always)]
@ -41,6 +49,7 @@ pub unsafe fn copy_forward(mut dest: *mut u8, mut src: *const u8, mut n: usize)
}
}
#[cfg(not(feature = "mem-unaligned"))]
#[inline(always)]
unsafe fn copy_forward_misaligned_words(dest: *mut u8, src: *const u8, n: usize) {
let mut dest_usize = dest as *mut usize;
@ -69,6 +78,20 @@ pub unsafe fn copy_forward(mut dest: *mut u8, mut src: *const u8, mut n: usize)
}
}
#[cfg(feature = "mem-unaligned")]
#[inline(always)]
unsafe fn copy_forward_misaligned_words(dest: *mut u8, src: *const u8, n: usize) {
let mut dest_usize = dest as *mut usize;
let mut src_usize = src as *mut usize;
let dest_end = dest.add(n) as *mut usize;
while dest_usize < dest_end {
*dest_usize = read_usize_unaligned(src_usize);
dest_usize = dest_usize.add(1);
src_usize = src_usize.add(1);
}
}
if n >= WORD_COPY_THRESHOLD {
// Align dest
// Because of n >= 2 * WORD_SIZE, dst_misalignment < n
@ -119,6 +142,7 @@ pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, mut n: usize) {
}
}
#[cfg(not(feature = "mem-unaligned"))]
#[inline(always)]
unsafe fn copy_backward_misaligned_words(dest: *mut u8, src: *const u8, n: usize) {
let mut dest_usize = dest as *mut usize;
@ -147,6 +171,20 @@ pub unsafe fn copy_backward(dest: *mut u8, src: *const u8, mut n: usize) {
}
}
#[cfg(feature = "mem-unaligned")]
#[inline(always)]
unsafe fn copy_backward_misaligned_words(dest: *mut u8, src: *const u8, n: usize) {
let mut dest_usize = dest as *mut usize;
let mut src_usize = src as *mut usize;
let dest_start = dest.sub(n) as *mut usize;
while dest_start < dest_usize {
dest_usize = dest_usize.sub(1);
src_usize = src_usize.sub(1);
*dest_usize = read_usize_unaligned(src_usize);
}
}
let mut dest = dest.add(n);
let mut src = src.add(n);