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See if this is the time we can remove layout::size_align #149109

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Merged
merged 1 commit into from
Nov 20, 2025
+16 −25
Merged

See if this is the time we can remove layout::size_align #149109

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16 changes: 1 addition & 15 deletions library/core/src/alloc/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,16 +10,6 @@ use crate::mem::SizedTypeProperties;
use crate::ptr::{Alignment, NonNull};
use crate::{assert_unsafe_precondition, fmt, mem};

// While this function is used in one place and its implementation
// could be inlined, the previous attempts to do so made rustc
// slower:
//
// * https://github.com/rust-lang/rust/pull/72189
// * https://github.com/rust-lang/rust/pull/79827
const fn size_align<T>() -> (usize, usize) {
(size_of::<T>(), align_of::<T>())
}

/// Layout of a block of memory.
///
/// An instance of `Layout` describes a particular layout of memory.
Expand Down Expand Up @@ -168,11 +158,7 @@ impl Layout {
#[must_use]
#[inline]
pub const fn new<T>() -> Self {
let (size, align) = size_align::<T>();
// SAFETY: if the type is instantiated, rustc already ensures that its
// layout is valid. Use the unchecked constructor to avoid inserting a
// panicking codepath that needs to be optimized out.
unsafe { Layout::from_size_align_unchecked(size, align) }
<T as SizedTypeProperties>::LAYOUT
}

/// Produces layout describing a record that could be used to
Expand Down
7 changes: 6 additions & 1 deletion library/core/src/mem/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1283,7 +1283,12 @@ pub trait SizedTypeProperties: Sized {

#[doc(hidden)]
#[unstable(feature = "sized_type_properties", issue = "none")]
const LAYOUT: Layout = Layout::new::<Self>();
const LAYOUT: Layout = {
// SAFETY: if the type is instantiated, rustc already ensures that its
// layout is valid. Use the unchecked constructor to avoid inserting a
// panicking codepath that needs to be optimized out.
unsafe { Layout::from_size_align_unchecked(Self::SIZE, Self::ALIGN) }
};

/// The largest safe length for a `[Self]`.
///
Expand Down
18 changes: 9 additions & 9 deletions tests/ui/thir-print/offset_of.stdout
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::concrete).10))
span: $DIR/offset_of.rs:37:5: 1430:57 (#0)
span: $DIR/offset_of.rs:37:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -117,7 +117,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::concrete).20))
span: $DIR/offset_of.rs:38:5: 1430:57 (#0)
span: $DIR/offset_of.rs:38:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -166,7 +166,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::concrete).30))
span: $DIR/offset_of.rs:39:5: 1430:57 (#0)
span: $DIR/offset_of.rs:39:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -215,7 +215,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::concrete).40))
span: $DIR/offset_of.rs:40:5: 1430:57 (#0)
span: $DIR/offset_of.rs:40:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -264,7 +264,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::concrete).50))
span: $DIR/offset_of.rs:41:5: 1430:57 (#0)
span: $DIR/offset_of.rs:41:5: 1435:57 (#0)
}
}
]
Expand Down Expand Up @@ -864,7 +864,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::generic).12))
span: $DIR/offset_of.rs:45:5: 1430:57 (#0)
span: $DIR/offset_of.rs:45:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -913,7 +913,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::generic).24))
span: $DIR/offset_of.rs:46:5: 1430:57 (#0)
span: $DIR/offset_of.rs:46:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -962,7 +962,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::generic).36))
span: $DIR/offset_of.rs:47:5: 1430:57 (#0)
span: $DIR/offset_of.rs:47:5: 1435:57 (#0)
}
}
Stmt {
Expand Down Expand Up @@ -1011,7 +1011,7 @@ body:
)
else_block: None
lint_level: Explicit(HirId(DefId(offset_of::generic).48))
span: $DIR/offset_of.rs:48:5: 1430:57 (#0)
span: $DIR/offset_of.rs:48:5: 1435:57 (#0)
}
}
]
Expand Down
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