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Support coercions and intrinsics for unsized ADTs - #4722

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Rust-GCC:masterfrom
nsvke:add-unsize
Aug 15, 2026
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Support coercions and intrinsics for unsized ADTs#4722
philberty merged 4 commits into
Rust-GCC:masterfrom
nsvke:add-unsize

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@nsvke nsvke commented Jul 24, 2026

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This patch introduces support for Dynamically Sized Types (DST) within
Algebraic Data Types (ADTs). Previously, the compiler embedded DST
fields directly into the ADT memory layout, even for ADTs following
unsize coercion rules. With this update, the compiler correctly
identifies unsized ADTs, preserves their static layout by avoiding
direct embedding, and appropriately generates fat pointers (containing
the data pointer and metadata) for references to these ADTs.

This patch adds basic support for ADT to ADT unsized coercions. It also
refactors the main coerce_unsized function into smaller helper functions
for better readability and maintainability.

This patch enables fundamental array-to-slice ([T; N] to [T])
unsized coercions. Previously, the compiler only handled dyn Trait
unsized coercions and immediately rejected array-to-slice conversions.
Now, the compiler correctly identifies valid array-to-slice coercions
and generates the appropriate Adjustment::UNSIZE tags.

This patch implements the 'unsize' lang item to the compiler.

@nsvke
nsvke force-pushed the add-unsize branch 3 times, most recently from 9c0d26f to 533d32e Compare July 27, 2026 10:54
@nsvke
nsvke force-pushed the add-unsize branch 2 times, most recently from 0704e97 to 9282cab Compare August 3, 2026 07:58
@nsvke

nsvke commented Aug 3, 2026

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@philberty

@nsvke
nsvke marked this pull request as draft August 4, 2026 16:06
@nsvke nsvke mentioned this pull request Aug 5, 2026
Merged
@nsvke
nsvke marked this pull request as ready for review August 5, 2026 09:12
nsvke added 4 commits August 9, 2026 14:35
@nsvke
lang: Add unsize
2170e07 
This patch implements the 'unsize' lang item to the compiler.

gcc/rust/ChangeLog:

	* typecheck/rust-tyty.cc (BaseType::unsize_to): New function.
	(BaseType::satisfies_bound): Use it.
	* typecheck/rust-tyty.h (class BaseType): New declaration.
	* util/rust-lang-item.cc (Rust::LangItem::lang_items): Add
	unsize to the BiMap.
	* util/rust-lang-item.h (class LangItem): Add UNSIZE to the Kind
	enum.

gcc/testsuite/ChangeLog:

	* rust/compile/unsize2.rs: New test.

Signed-off-by: Enes Cevik <enes@nsvke.com>
@nsvke
typecheck: Add array to slice unsize coercion support
df77cff 
This patch enables fundamental array-to-slice (`[T; N]` to `[T]`)
unsized coercions. Previously, the compiler only handled `dyn Trait`
unsized coercions and immediately rejected array-to-slice conversions.
Now, the compiler correctly identifies valid array-to-slice coercions
and generates the appropriate `Adjustment::UNSIZE` tags.

gcc/rust/ChangeLog:

	* typecheck/rust-coercion.cc
	(TypeCoercionRules::coerce_unsized): Add array-to-slice coercion
	support.

gcc/testsuite/ChangeLog:

	* rust/compile/coercion.rs: New test.

Signed-off-by: Enes Cevik <enes@nsvke.com>
@nsvke
typecheck: Add ADT to ADT unsize coercion support
5f8edd4 
This patch adds basic support for ADT to ADT unsized coercions. It also
refactors the main coerce_unsized function into smaller helper functions
for better readability and maintainability.

gcc/rust/ChangeLog:

	* backend/rust-compile-base.h (resolve_adjustments): Fix typo.
	(resolve_unsized_adt_adjustment): New declaration.
	* backend/rust-compile-expr.cc (CompileExpr::visit): Fix typo.
	(HIRCompileBase::resolve_unsized_adt_adjustment): New function.
	(HIRCompileBase::resolve_unsized_adjustment): Use it.
	(CompileExpr::generate_possible_fn_trait_call): Likewise.
	(HIRCompileBase::coercion_site): Fix typo.
	* typecheck/rust-coercion.cc
	(TypeCoercionRules::coerce_unsized): Use helper functions.
	(TypeCoercionRules::unwrap_ptrs_and_refs): New function.
	(TypeCoercionRules::coerce_unsized_array_to_slice): Likewise.
	(TypeCoercionRules::coerce_unsized_dyn): Likewise.
	(TypeCoercionRules::coerce_unsized_adt): Liksewise.
	(TypeCoercionRules::apply_reborrow_adjustment): Likewise.
	* typecheck/rust-coercion.h (struct CoercionSetup): New struct.
	(coerce_unsized): Add is_inner parameter.
	(unwrap_ptrs_and_refs): New declaration.
	(coerce_unsized_array_to_slice): Likewise.
	(coerce_unsized_dyn): Likewise.
	(coerce_unsized_adt): Likewise.
	* util/rust-lang-item.cc (Rust::LangItem::lang_items): Add
	coerce_unsized to the BiMap.
	* util/rust-lang-item.h (class LangItem): Add COERCE_UNSIZED to
	the Kind enum.

gcc/testsuite/ChangeLog:

	* rust/compile/coercion2.rs: New test.

Signed-off-by: Enes Cevik <enes@nsvke.com>
@nsvke
backend: Add DST ADT support
a866d9a 
This patch introduces support for Dynamically Sized Types (DST) within
Algebraic Data Types (ADTs). Previously, the compiler embedded DST
fields directly into the ADT memory layout, even for ADTs following
unsize coercion rules. With this update, the compiler correctly
identifies unsized ADTs, preserves their static layout by avoiding
direct embedding, and appropriately generates fat pointers (containing
the data pointer and metadata) for references to these ADTs.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Add
	indirect field access for DST's and new borrow approach for fat
	pointers.
	(resolve_unsized_adt_adjustment): Correct GIMPLE generation for
	nested unsized ADTs.
	* backend/rust-compile-type.cc (TyTyResolveCompile::visit): Add
	DST ADT support.
	(TyTyResolveCompile::create_dyn_adt_record): New function.
	* backend/rust-compile-type.h (create_dyn_adt_record): New
	declaration.
	* backend/rust-intrinsic-handlers.cc (get_inner_dst): New
	function.
	(size_of_val_handler): Add DST ADT support.
	(min_align_of_val_handler): Likewise.
	* typecheck/rust-coercion.cc
	(TypeCoercionRules::coerce_unsized_adt): Skip zero-sized fields
	during coercion.
	* backend/rust-compile.cc (HIRCompileBase::coerce_to_dyn_object):
	Remove unnecessary ref wrapping.
	* typecheck/rust-tyty.cc (ADTType::is_unsized): New function.
	(ReferenceType::is_dyn_object): Add DST ADT support.
	(ReferenceType::is_dyn_adt_type): New function.
	(PointerType::is_dyn_object): Add DST ADT support.
	(PointerType::is_dyn_adt_type): New function.
	* typecheck/rust-tyty.h (is_unsized): New declaration.

gcc/testsuite/ChangeLog:

	* rust/execute/unsized-adt-nested-coercion.rs: New test.
	* rust/execute/unsized-adt-size.rs: New test.

Signed-off-by: Enes Cevik <enes@nsvke.com>
philberty
philberty approved these changes Aug 15, 2026
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LGTM

@philberty
philberty added this pull request to the merge queue Aug 15, 2026
Merged via the queue into Rust-GCC:master with commit 53122e3 Aug 15, 2026
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@philberty philberty philberty approved these changes
@P-E-P P-E-P Awaiting requested review from P-E-P
@CohenArthur CohenArthur Awaiting requested review from CohenArthur

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@nsvke @philberty