From eb584a23bfba55512af0a223cf4133b806ede178 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sat, 8 Jun 2024 11:26:56 +0200 Subject: [PATCH] offset_of: allow (unstably) taking the offset of slice tail fields --- compiler/rustc_codegen_cranelift/src/base.rs | 7 ++-- compiler/rustc_codegen_ssa/src/mir/rvalue.rs | 5 ++- .../rustc_const_eval/src/interpret/step.rs | 5 ++- compiler/rustc_feature/src/unstable.rs | 2 ++ compiler/rustc_hir_typeck/src/expr.rs | 35 +++++++++++++++---- .../rustc_hir_typeck/src/fn_ctxt/_impl.rs | 20 +++++++++++ compiler/rustc_middle/src/ty/layout.rs | 34 ++++++++++++++++++ .../src/dataflow_const_prop.rs | 10 +++--- compiler/rustc_mir_transform/src/gvn.rs | 10 +++--- .../src/known_panics_lint.rs | 7 ++-- compiler/rustc_span/src/symbol.rs | 1 + compiler/rustc_target/src/abi/mod.rs | 23 ------------ .../feature-gate-offset-of-slice.rs | 26 ++++++++++++++ .../feature-gate-offset-of-slice.stderr | 35 +++++++++++++++++++ tests/ui/offset-of/offset-of-dst-field.rs | 4 +++ tests/ui/offset-of/offset-of-dst-field.stderr | 11 +++++- tests/ui/offset-of/offset-of-slice.rs | 26 ++++++++++++++ 17 files changed, 215 insertions(+), 46 deletions(-) create mode 100644 tests/ui/feature-gates/feature-gate-offset-of-slice.rs create mode 100644 tests/ui/feature-gates/feature-gate-offset-of-slice.stderr create mode 100644 tests/ui/offset-of/offset-of-slice.rs diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs index 963e5de91ce..6d26ca0b899 100644 --- a/compiler/rustc_codegen_cranelift/src/base.rs +++ b/compiler/rustc_codegen_cranelift/src/base.rs @@ -832,9 +832,10 @@ fn codegen_stmt<'tcx>( let val = match null_op { NullOp::SizeOf => layout.size.bytes(), NullOp::AlignOf => layout.align.abi.bytes(), - NullOp::OffsetOf(fields) => { - layout.offset_of_subfield(fx, fields.iter()).bytes() - } + NullOp::OffsetOf(fields) => fx + .tcx + .offset_of_subfield(ParamEnv::reveal_all(), layout, fields.iter()) + .bytes(), NullOp::UbChecks => { let val = fx.tcx.sess.ub_checks(); let val = CValue::by_val( diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs index c23867be3a1..ad6b3f1159d 100644 --- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs +++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs @@ -680,7 +680,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { bx.cx().const_usize(val) } mir::NullOp::OffsetOf(fields) => { - let val = layout.offset_of_subfield(bx.cx(), fields.iter()).bytes(); + let val = bx + .tcx() + .offset_of_subfield(bx.param_env(), layout, fields.iter()) + .bytes(); bx.cx().const_usize(val) } mir::NullOp::UbChecks => { diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs index d0bb821862a..1baf62baa81 100644 --- a/compiler/rustc_const_eval/src/interpret/step.rs +++ b/compiler/rustc_const_eval/src/interpret/step.rs @@ -253,7 +253,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> { Scalar::from_target_usize(val, self) } mir::NullOp::OffsetOf(fields) => { - let val = layout.offset_of_subfield(self, fields.iter()).bytes(); + let val = self + .tcx + .offset_of_subfield(self.param_env, layout, fields.iter()) + .bytes(); Scalar::from_target_usize(val, self) } mir::NullOp::UbChecks => Scalar::from_bool(self.tcx.sess.ub_checks()), diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs index d67422849d8..2410019868a 100644 --- a/compiler/rustc_feature/src/unstable.rs +++ b/compiler/rustc_feature/src/unstable.rs @@ -559,6 +559,8 @@ declare_features! ( (unstable, offset_of_enum, "1.75.0", Some(120141)), /// Allows using multiple nested field accesses in offset_of! (unstable, offset_of_nested, "1.77.0", Some(120140)), + /// Allows using fields with slice type in offset_of! + (unstable, offset_of_slice, "CURRENT_RUSTC_VERSION", Some(126151)), /// Allows using `#[optimize(X)]`. (unstable, optimize_attribute, "1.34.0", Some(54882)), /// Allows postfix match `expr.match { ... }` diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs index d5d360ca047..5b27ebe3416 100644 --- a/compiler/rustc_hir_typeck/src/expr.rs +++ b/compiler/rustc_hir_typeck/src/expr.rs @@ -3363,7 +3363,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { let field_ty = self.field_ty(expr.span, field, args); - // FIXME: DSTs with static alignment should be allowed + // Enums are anyway always sized. But just to safeguard against future + // language extensions, let's double-check. self.require_type_is_sized(field_ty, expr.span, ObligationCauseCode::Misc); if field.vis.is_accessible_from(sub_def_scope, self.tcx) { @@ -3391,8 +3392,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { { let field_ty = self.field_ty(expr.span, field, args); - // FIXME: DSTs with static alignment should be allowed - self.require_type_is_sized(field_ty, expr.span, ObligationCauseCode::Misc); + if self.tcx.features().offset_of_slice { + self.require_type_has_static_alignment( + field_ty, + expr.span, + ObligationCauseCode::Misc, + ); + } else { + self.require_type_is_sized( + field_ty, + expr.span, + ObligationCauseCode::Misc, + ); + } if field.vis.is_accessible_from(def_scope, self.tcx) { self.tcx.check_stability(field.did, Some(expr.hir_id), expr.span, None); @@ -3412,10 +3424,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { if let Ok(index) = field.as_str().parse::() && field.name == sym::integer(index) { - for ty in tys.iter().take(index + 1) { - self.require_type_is_sized(ty, expr.span, ObligationCauseCode::Misc); - } if let Some(&field_ty) = tys.get(index) { + if self.tcx.features().offset_of_slice { + self.require_type_has_static_alignment( + field_ty, + expr.span, + ObligationCauseCode::Misc, + ); + } else { + self.require_type_is_sized( + field_ty, + expr.span, + ObligationCauseCode::Misc, + ); + } + field_indices.push((FIRST_VARIANT, index.into())); current_container = field_ty; diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs index 85c6d4dc12c..e354e1ec59c 100644 --- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs +++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs @@ -386,6 +386,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { } } + pub fn require_type_has_static_alignment( + &self, + ty: Ty<'tcx>, + span: Span, + code: traits::ObligationCauseCode<'tcx>, + ) { + if !ty.references_error() { + let tail = + self.tcx.struct_tail_with_normalize(ty, |ty| self.normalize(span, ty), || {}); + // Sized types have static alignment, and so do slices. + if tail.is_trivially_sized(self.tcx) || matches!(tail.kind(), ty::Slice(..)) { + // Nothing else is required here. + } else { + // We can't be sure, let's required full `Sized`. + let lang_item = self.tcx.require_lang_item(LangItem::Sized, None); + self.require_type_meets(ty, span, code, lang_item); + } + } + } + pub fn register_bound( &self, ty: Ty<'tcx>, diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs index 142872009bf..56945bf6be4 100644 --- a/compiler/rustc_middle/src/ty/layout.rs +++ b/compiler/rustc_middle/src/ty/layout.rs @@ -1351,3 +1351,37 @@ pub trait FnAbiOf<'tcx>: FnAbiOfHelpers<'tcx> { } impl<'tcx, C: FnAbiOfHelpers<'tcx>> FnAbiOf<'tcx> for C {} + +impl<'tcx> TyCtxt<'tcx> { + pub fn offset_of_subfield( + self, + param_env: ty::ParamEnv<'tcx>, + mut layout: TyAndLayout<'tcx>, + indices: I, + ) -> Size + where + I: Iterator, + { + let cx = LayoutCx { tcx: self, param_env }; + let mut offset = Size::ZERO; + + for (variant, field) in indices { + layout = layout.for_variant(&cx, variant); + let index = field.index(); + offset += layout.fields.offset(index); + layout = layout.field(&cx, index); + if !layout.is_sized() { + // If it is not sized, then the tail must still have at least a known static alignment. + let tail = self.struct_tail_erasing_lifetimes(layout.ty, param_env); + if !matches!(tail.kind(), ty::Slice(..)) { + bug!( + "offset of not-statically-aligned field (type {:?}) cannot be computed statically", + layout.ty + ); + } + } + } + + offset + } +} diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index a8caead46f2..eba5d13d33f 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -10,7 +10,7 @@ use rustc_middle::bug; use rustc_middle::mir::interpret::{InterpResult, Scalar}; use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor}; use rustc_middle::mir::*; -use rustc_middle::ty::layout::LayoutOf; +use rustc_middle::ty::layout::{HasParamEnv, LayoutOf}; use rustc_middle::ty::{self, Ty, TyCtxt}; use rustc_mir_dataflow::value_analysis::{ Map, PlaceIndex, State, TrackElem, ValueAnalysis, ValueAnalysisWrapper, ValueOrPlace, @@ -285,9 +285,11 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> { let val = match null_op { NullOp::SizeOf if layout.is_sized() => layout.size.bytes(), NullOp::AlignOf if layout.is_sized() => layout.align.abi.bytes(), - NullOp::OffsetOf(fields) => { - layout.offset_of_subfield(&self.ecx, fields.iter()).bytes() - } + NullOp::OffsetOf(fields) => self + .ecx + .tcx + .offset_of_subfield(self.ecx.param_env(), layout, fields.iter()) + .bytes(), _ => return ValueOrPlace::Value(FlatSet::Top), }; FlatSet::Elem(Scalar::from_target_usize(val, &self.tcx)) diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs index acde16fcb75..ebfb372329e 100644 --- a/compiler/rustc_mir_transform/src/gvn.rs +++ b/compiler/rustc_mir_transform/src/gvn.rs @@ -95,7 +95,7 @@ use rustc_middle::bug; use rustc_middle::mir::interpret::GlobalAlloc; use rustc_middle::mir::visit::*; use rustc_middle::mir::*; -use rustc_middle::ty::layout::LayoutOf; +use rustc_middle::ty::layout::{HasParamEnv, LayoutOf}; use rustc_middle::ty::{self, Ty, TyCtxt}; use rustc_span::def_id::DefId; use rustc_span::DUMMY_SP; @@ -484,9 +484,11 @@ impl<'body, 'tcx> VnState<'body, 'tcx> { let val = match null_op { NullOp::SizeOf => layout.size.bytes(), NullOp::AlignOf => layout.align.abi.bytes(), - NullOp::OffsetOf(fields) => { - layout.offset_of_subfield(&self.ecx, fields.iter()).bytes() - } + NullOp::OffsetOf(fields) => self + .ecx + .tcx + .offset_of_subfield(self.ecx.param_env(), layout, fields.iter()) + .bytes(), NullOp::UbChecks => return None, }; let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap(); diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs index 8b46658b322..47bbddbc31d 100644 --- a/compiler/rustc_mir_transform/src/known_panics_lint.rs +++ b/compiler/rustc_mir_transform/src/known_panics_lint.rs @@ -625,9 +625,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { let val = match null_op { NullOp::SizeOf => op_layout.size.bytes(), NullOp::AlignOf => op_layout.align.abi.bytes(), - NullOp::OffsetOf(fields) => { - op_layout.offset_of_subfield(self, fields.iter()).bytes() - } + NullOp::OffsetOf(fields) => self + .tcx + .offset_of_subfield(self.param_env, op_layout, fields.iter()) + .bytes(), NullOp::UbChecks => return None, }; ImmTy::from_scalar(Scalar::from_target_usize(val, self), layout).into() diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs index 93594264167..e245dfb9f5d 100644 --- a/compiler/rustc_span/src/symbol.rs +++ b/compiler/rustc_span/src/symbol.rs @@ -1304,6 +1304,7 @@ symbols! { offset_of, offset_of_enum, offset_of_nested, + offset_of_slice, ok_or_else, omit_gdb_pretty_printer_section, on, diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs index 666efd9deca..737e9a8eab0 100644 --- a/compiler/rustc_target/src/abi/mod.rs +++ b/compiler/rustc_target/src/abi/mod.rs @@ -256,29 +256,6 @@ impl<'a, Ty> TyAndLayout<'a, Ty> { Ty::is_transparent(self) } - pub fn offset_of_subfield(self, cx: &C, indices: I) -> Size - where - Ty: TyAbiInterface<'a, C>, - I: Iterator, - { - let mut layout = self; - let mut offset = Size::ZERO; - - for (variant, field) in indices { - layout = layout.for_variant(cx, variant); - let index = field.index(); - offset += layout.fields.offset(index); - layout = layout.field(cx, index); - assert!( - layout.is_sized(), - "offset of unsized field (type {:?}) cannot be computed statically", - layout.ty - ); - } - - offset - } - /// Finds the one field that is not a 1-ZST. /// Returns `None` if there are multiple non-1-ZST fields or only 1-ZST-fields. pub fn non_1zst_field(&self, cx: &C) -> Option<(usize, Self)> diff --git a/tests/ui/feature-gates/feature-gate-offset-of-slice.rs b/tests/ui/feature-gates/feature-gate-offset-of-slice.rs new file mode 100644 index 00000000000..23e8668bc68 --- /dev/null +++ b/tests/ui/feature-gates/feature-gate-offset-of-slice.rs @@ -0,0 +1,26 @@ +use std::mem::offset_of; + +struct S { + a: u8, + b: (u8, u8), + c: [i32], +} + +struct T { + x: i32, + y: S, +} + +type Tup = (i32, [i32]); + +fn main() { + offset_of!(S, c); //~ ERROR size for values of type `[i32]` cannot be known at compilation time +} + +fn other() { + offset_of!(T, y); //~ ERROR size for values of type `[i32]` cannot be known at compilation time +} + +fn tuple() { + offset_of!(Tup, 1); //~ ERROR size for values of type `[i32]` cannot be known at compilation time +} diff --git a/tests/ui/feature-gates/feature-gate-offset-of-slice.stderr b/tests/ui/feature-gates/feature-gate-offset-of-slice.stderr new file mode 100644 index 00000000000..5cf34a897f4 --- /dev/null +++ b/tests/ui/feature-gates/feature-gate-offset-of-slice.stderr @@ -0,0 +1,35 @@ +error[E0277]: the size for values of type `[i32]` cannot be known at compilation time + --> $DIR/feature-gate-offset-of-slice.rs:17:5 + | +LL | offset_of!(S, c); + | ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: the trait `Sized` is not implemented for `[i32]` + = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0277]: the size for values of type `[i32]` cannot be known at compilation time + --> $DIR/feature-gate-offset-of-slice.rs:21:5 + | +LL | offset_of!(T, y); + | ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: within `S`, the trait `Sized` is not implemented for `[i32]`, which is required by `S: Sized` +note: required because it appears within the type `S` + --> $DIR/feature-gate-offset-of-slice.rs:3:8 + | +LL | struct S { + | ^ + = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info) + +error[E0277]: the size for values of type `[i32]` cannot be known at compilation time + --> $DIR/feature-gate-offset-of-slice.rs:25:5 + | +LL | offset_of!(Tup, 1); + | ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: the trait `Sized` is not implemented for `[i32]` + = note: this error originates in the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info) + +error: aborting due to 3 previous errors + +For more information about this error, try `rustc --explain E0277`. diff --git a/tests/ui/offset-of/offset-of-dst-field.rs b/tests/ui/offset-of/offset-of-dst-field.rs index 016ebfadd14..5ae15f32357 100644 --- a/tests/ui/offset-of/offset-of-dst-field.rs +++ b/tests/ui/offset-of/offset-of-dst-field.rs @@ -49,3 +49,7 @@ fn delta() { fn generic_with_maybe_sized() -> usize { offset_of!(Delta, z) //~ ERROR the size for values of type } + +fn illformed_tuple() { + offset_of!(([u8], u8), 1); //~ ERROR the size for values of type +} diff --git a/tests/ui/offset-of/offset-of-dst-field.stderr b/tests/ui/offset-of/offset-of-dst-field.stderr index adfd16c6f2b..bcfe796897e 100644 --- a/tests/ui/offset-of/offset-of-dst-field.stderr +++ b/tests/ui/offset-of/offset-of-dst-field.stderr @@ -81,6 +81,15 @@ LL - fn generic_with_maybe_sized() -> usize { LL + fn generic_with_maybe_sized() -> usize { | -error: aborting due to 8 previous errors +error[E0277]: the size for values of type `[u8]` cannot be known at compilation time + --> $DIR/offset-of-dst-field.rs:54:16 + | +LL | offset_of!(([u8], u8), 1); + | ^^^^^^^^^^ doesn't have a size known at compile-time + | + = help: the trait `Sized` is not implemented for `[u8]` + = note: only the last element of a tuple may have a dynamically sized type + +error: aborting due to 9 previous errors For more information about this error, try `rustc --explain E0277`. diff --git a/tests/ui/offset-of/offset-of-slice.rs b/tests/ui/offset-of/offset-of-slice.rs new file mode 100644 index 00000000000..a0fe3198f68 --- /dev/null +++ b/tests/ui/offset-of/offset-of-slice.rs @@ -0,0 +1,26 @@ +//@run-pass +#![feature(offset_of_slice, offset_of_nested)] + +use std::mem::offset_of; + +#[repr(C)] +struct S { + a: u8, + b: (u8, u8), + c: [i32], +} + +#[repr(C)] +struct T { + x: i8, + y: S, +} + +type Tup = (i16, [i32]); + +fn main() { + assert_eq!(offset_of!(S, c), 4); + assert_eq!(offset_of!(T, y), 4); + assert_eq!(offset_of!(T, y.c), 8); + assert_eq!(offset_of!(Tup, 1), 4); +}