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Detect and optimize SIMD-like struct #146049
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -566,6 +566,55 @@ fn layout_of_uncached<'tcx>( | |
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| // ADTs. | ||
| ty::Adt(def, args) => { | ||
| // SIMD-like struct detection and optimization with conservative safety constraints | ||
| // Check if this is a user-defined struct like Vector<T, const N: usize>([T; N]) | ||
| // that should be treated as SIMD-friendly even without #[repr(simd)] | ||
| if def.is_struct() | ||
| && def.variants().len() == 1 | ||
| && def.variant(FIRST_VARIANT).fields.len() == 1 | ||
| && def.did().is_local() // Only user crate types | ||
| { | ||
| // Safety: exclude system crates by checking crate name | ||
| let crate_name = tcx.crate_name(def.did().krate); | ||
| let crate_name_str = crate_name.as_str(); | ||
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| // Exclude known system/compiler crates | ||
| if !matches!(crate_name_str, | ||
| "core" | "std" | "alloc" | "proc_macro" | "test" | | ||
| "rustc_std_workspace_core" | "rustc_std_workspace_alloc" | | ||
| "compiler_builtins" | "libc" | "unwind" | "panic_abort" | | ||
| "panic_unwind" | "adler2" | "object" | "memchr" | ||
| ) { | ||
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Comment on lines
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Why do these get special treatment? Name matching specific ecosystem crates to give them special treatment is very hazardous. Occasionally we need to match std crates, for which we have the list at rust/compiler/rustc_span/src/symbol.rs Line 2444 in 64a99db
pub const STDLIB_STABLE_CRATES: &[Symbol] = &[sym::std, sym::core, sym::alloc, sym::proc_macro];
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| let field_ty = def.variant(FIRST_VARIANT).fields[FieldIdx::ZERO].ty(tcx, args); | ||
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| // Check if the single field is an array of SIMD-friendly types | ||
| if let ty::Array(element_ty, array_len) = field_ty.kind() { | ||
| if is_simd_friendly_element_type(*element_ty) { | ||
| if let Some(len) = extract_const_value(cx, ty, *array_len)? | ||
| .try_to_target_usize(tcx) | ||
| { | ||
| // Common SIMD sizes: 4, 8, 16 (conservative range) | ||
| if matches!(len, 4 | 8 | 16) { | ||
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Comment on lines
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Use a |
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| // REQUIRE explicit alignment hint - this is the key safety measure | ||
| let has_simd_alignment = def.repr().align | ||
| .map_or(false, |align| { | ||
| let align_bytes = align.bytes(); | ||
| // Must have 16+ byte alignment to suggest SIMD intent | ||
| align_bytes >= 16 && align_bytes.is_power_of_two() | ||
| }); | ||
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| // Only apply if user explicitly requested SIMD-like alignment | ||
| if has_simd_alignment { | ||
| let e_ly = cx.layout_of(*element_ty)?; | ||
| return Ok(map_layout(cx.calc.simd_type(e_ly, len, false))?); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| // Cache the field layouts. | ||
| let variants = def | ||
| .variants() | ||
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@@ -706,6 +755,21 @@ fn layout_of_uncached<'tcx>( | |
| }) | ||
| } | ||
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| /// Check if a type is suitable for SIMD operations | ||
| fn is_simd_friendly_element_type<'tcx>(ty: Ty<'tcx>) -> bool { | ||
| match ty.kind() { | ||
| // Floating-point types - most common SIMD use case | ||
| ty::Float(_) => true, | ||
| // Integer types - common for SIMD | ||
| ty::Int(_) | ty::Uint(_) => true, | ||
| // Bool can be vectorized in some contexts | ||
| ty::Bool => true, | ||
| // Pointers removed to avoid affecting system types like TypeId | ||
| // Other types are not typically vectorizable | ||
| _ => false, | ||
| } | ||
| } | ||
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| fn record_layout_for_printing<'tcx>(cx: &LayoutCx<'tcx>, layout: TyAndLayout<'tcx>) { | ||
| // Ignore layouts that are done with non-empty environments or | ||
| // non-monomorphic layouts, as the user only wants to see the stuff | ||
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