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Remove may_use_unaligned_api #100

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Sep 14, 2023
Merged

Remove may_use_unaligned_api #100

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45 changes: 3 additions & 42 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,33 +29,6 @@ use core::alloc::{GlobalAlloc, Layout};
use core::ffi::c_void;
use ffi::*;

// `MI_MAX_ALIGN_SIZE` is 16 unless manually overridden:
// https://github.com/microsoft/mimalloc/blob/15220c68/include/mimalloc-types.h#L22
//
// If it changes on us, we should consider either manually overriding it, or
// expose it from the -sys crate (in order to catch updates)
const MI_MAX_ALIGN_SIZE: usize = 16;

// Note: this doesn't take a layout directly because doing so would be wrong for
// reallocation
#[inline]
fn may_use_unaligned_api(size: usize, alignment: usize) -> bool {
// Required by `GlobalAlloc`. Note that while allocators aren't allowed to
// unwind in rust, this is only in debug mode, and can only happen if the
// caller already caused UB by passing in an invalid layout.
debug_assert!(size != 0 && alignment.is_power_of_two());

// This logic is based on the discussion [here]. We don't bother with the
// 3rd suggested test due to it being high cost (calling `mi_good_size`)
// compared to the other checks, and also feeling like it relies on too much
// implementation-specific behavior.
//
// [here]: https://github.com/microsoft/mimalloc/issues/314#issuecomment-708541845

(alignment <= MI_MAX_ALIGN_SIZE && size >= alignment)
|| (alignment == size && alignment <= 4096)
}

/// Drop-in mimalloc global allocator.
///
/// ## Usage
Expand All @@ -70,20 +43,12 @@ pub struct MiMalloc;
unsafe impl GlobalAlloc for MiMalloc {
#[inline]
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
if may_use_unaligned_api(layout.size(), layout.align()) {
mi_malloc(layout.size()) as *mut u8
} else {
mi_malloc_aligned(layout.size(), layout.align()) as *mut u8
}
mi_malloc_aligned(layout.size(), layout.align()) as *mut u8
}

#[inline]
unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
if may_use_unaligned_api(layout.size(), layout.align()) {
mi_zalloc(layout.size()) as *mut u8
} else {
mi_zalloc_aligned(layout.size(), layout.align()) as *mut u8
}
mi_zalloc_aligned(layout.size(), layout.align()) as *mut u8
}

#[inline]
Expand All @@ -93,11 +58,7 @@ unsafe impl GlobalAlloc for MiMalloc {

#[inline]
unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
if may_use_unaligned_api(new_size, layout.align()) {
mi_realloc(ptr as *mut c_void, new_size) as *mut u8
} else {
mi_realloc_aligned(ptr as *mut c_void, new_size, layout.align()) as *mut u8
}
mi_realloc_aligned(ptr as *mut c_void, new_size, layout.align()) as *mut u8
}
}

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