diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs index 20b6561f8b2..8c364a4f3b2 100644 --- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs +++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs @@ -363,6 +363,8 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) { sym::likely => (0, vec![tcx.types.bool], tcx.types.bool), sym::unlikely => (0, vec![tcx.types.bool], tcx.types.bool), + sym::read_via_copy => (1, vec![tcx.mk_imm_ptr(param(0))], param(0)), + sym::discriminant_value => { let assoc_items = tcx.associated_item_def_ids( tcx.require_lang_item(hir::LangItem::DiscriminantKind, None), diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs index 46ec1a2dca1..91966e75b5f 100644 --- a/compiler/rustc_lint_defs/src/builtin.rs +++ b/compiler/rustc_lint_defs/src/builtin.rs @@ -1026,12 +1026,13 @@ declare_lint! { /// ### Example /// /// ```rust,compile_fail - /// #![feature(const_ptr_read)] + /// #![feature(const_mut_refs)] /// const FOO: () = unsafe { /// let x = &[0_u8; 4]; /// let y = x.as_ptr().cast::(); - /// y.read(); // the address of a `u8` array is unknown and thus we don't know if - /// // it is aligned enough for reading a `u32`. + /// let mut z = 123; + /// y.copy_to_nonoverlapping(&mut z, 1); // the address of a `u8` array is unknown + /// // and thus we don't know if it is aligned enough for copying a `u32`. /// }; /// ``` /// diff --git a/compiler/rustc_mir_transform/src/lower_intrinsics.rs b/compiler/rustc_mir_transform/src/lower_intrinsics.rs index f596cc1808f..151fff27d14 100644 --- a/compiler/rustc_mir_transform/src/lower_intrinsics.rs +++ b/compiler/rustc_mir_transform/src/lower_intrinsics.rs @@ -149,6 +149,30 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics { terminator.kind = TerminatorKind::Goto { target }; } } + sym::read_via_copy => { + let Ok([arg]) = <[_; 1]>::try_from(std::mem::take(args)) else { + span_bug!(terminator.source_info.span, "Wrong number of arguments"); + }; + let derefed_place = + if let Some(place) = arg.place() && let Some(local) = place.as_local() { + tcx.mk_place_deref(local.into()) + } else { + span_bug!(terminator.source_info.span, "Only passing a local is supported"); + }; + block.statements.push(Statement { + source_info: terminator.source_info, + kind: StatementKind::Assign(Box::new(( + *destination, + Rvalue::Use(Operand::Copy(derefed_place)), + ))), + }); + if let Some(target) = *target { + terminator.kind = TerminatorKind::Goto { target }; + } else { + // Reading something uninhabited means this is unreachable. + terminator.kind = TerminatorKind::Unreachable; + } + } sym::discriminant_value => { if let (Some(target), Some(arg)) = (*target, args[0].place()) { let arg = tcx.mk_place_deref(arg); diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs index 4e626fd9f30..45f79c9d805 100644 --- a/compiler/rustc_span/src/symbol.rs +++ b/compiler/rustc_span/src/symbol.rs @@ -1153,6 +1153,7 @@ symbols! { read_enum_variant_arg, read_struct, read_struct_field, + read_via_copy, readonly, realloc, reason, diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs index c6321587adc..d77c2a00eb7 100644 --- a/library/core/src/intrinsics.rs +++ b/library/core/src/intrinsics.rs @@ -2020,6 +2020,20 @@ extern "rust-intrinsic" { #[rustc_safe_intrinsic] pub fn saturating_sub(a: T, b: T) -> T; + /// This is a *typed* read, `copy *p` in MIR. + /// + /// The stabilized form of this intrinsic is [`crate::ptr::read`], so + /// that can be implemented without needing to do an *untyped* copy + /// via [`copy_nonoverlapping`], and thus can get proper metadata. + /// + /// This intrinsic can *only* be called with a copy or move of a local. + /// (It allows neither constants nor projections.) + /// + /// To avoid introducing any `noalias` requirements, it just takes a pointer. + #[cfg(not(bootstrap))] + #[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")] + pub fn read_via_copy(p: *const T) -> T; + /// Returns the value of the discriminant for the variant in 'v'; /// if `T` has no discriminant, returns `0`. /// diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs index f41be46abc9..04b67a56db5 100644 --- a/library/core/src/ptr/mod.rs +++ b/library/core/src/ptr/mod.rs @@ -1137,25 +1137,33 @@ pub const unsafe fn replace(dst: *mut T, mut src: T) -> T { pub const unsafe fn read(src: *const T) -> T { // We are calling the intrinsics directly to avoid function calls in the generated code // as `intrinsics::copy_nonoverlapping` is a wrapper function. + #[cfg(bootstrap)] extern "rust-intrinsic" { #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")] fn copy_nonoverlapping(src: *const T, dst: *mut T, count: usize); } - let mut tmp = MaybeUninit::::uninit(); // SAFETY: the caller must guarantee that `src` is valid for reads. // `src` cannot overlap `tmp` because `tmp` was just allocated on // the stack as a separate allocated object. - // - // Also, since we just wrote a valid value into `tmp`, it is guaranteed - // to be properly initialized. unsafe { assert_unsafe_precondition!( "ptr::read requires that the pointer argument is aligned and non-null", [T](src: *const T) => is_aligned_and_not_null(src) ); - copy_nonoverlapping(src, tmp.as_mut_ptr(), 1); - tmp.assume_init() + + #[cfg(bootstrap)] + { + let mut tmp = MaybeUninit::::uninit(); + copy_nonoverlapping(src, tmp.as_mut_ptr(), 1); + tmp.assume_init() + } + #[cfg(not(bootstrap))] + { + // This uses a dedicated intrinsic, not `copy_nonoverlapping`, + // so that it gets a *typed* copy, not an *untyped* one. + crate::intrinsics::read_via_copy(src) + } } } diff --git a/tests/codegen/mem-replace-direct-memcpy.rs b/tests/codegen/mem-replace-direct-memcpy.rs index e8bbf0e1bbd..3b01a621b56 100644 --- a/tests/codegen/mem-replace-direct-memcpy.rs +++ b/tests/codegen/mem-replace-direct-memcpy.rs @@ -12,13 +12,44 @@ pub fn replace_byte(dst: &mut u8, src: u8) -> u8 { std::mem::replace(dst, src) } +#[repr(C, align(8))] +pub struct Big([u64; 7]); +pub fn replace_big(dst: &mut Big, src: Big) -> Big { + // Before the `read_via_copy` intrinsic, this emitted six `memcpy`s. + std::mem::replace(dst, src) +} + // NOTE(eddyb) the `CHECK-NOT`s ensure that the only calls of `@llvm.memcpy` in -// the entire output, are the two direct calls we want, from `ptr::replace`. +// the entire output, are the direct calls we want, from `ptr::replace`. // CHECK-NOT: call void @llvm.memcpy -// CHECK: ; core::mem::replace + +// For a large type, we expect exactly three `memcpy`s +// CHECK-LABEL: define internal void @{{.+}}mem{{.+}}replace{{.+}}sret(%Big) + // CHECK-NOT: alloca + // CHECK: alloca %Big + // CHECK-NOT: alloca + // CHECK-NOT: call void @llvm.memcpy + // CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false) + // CHECK-NOT: call void @llvm.memcpy + // CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false) + // CHECK-NOT: call void @llvm.memcpy + // CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false) + // CHECK-NOT: call void @llvm.memcpy + // CHECK-NOT: call void @llvm.memcpy -// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false) -// CHECK-NOT: call void @llvm.memcpy -// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false) + +// For a small type, we expect one each of `load`/`store`/`memcpy` instead +// CHECK-LABEL: define internal noundef i8 @{{.+}}mem{{.+}}replace + // CHECK-NOT: alloca + // CHECK: alloca i8 + // CHECK-NOT: alloca + // CHECK-NOT: call void @llvm.memcpy + // CHECK: load i8 + // CHECK-NOT: call void @llvm.memcpy + // CHECK: store i8 + // CHECK-NOT: call void @llvm.memcpy + // CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, i1 false) + // CHECK-NOT: call void @llvm.memcpy + // CHECK-NOT: call void @llvm.memcpy diff --git a/tests/codegen/read-noundef-metadata.rs b/tests/codegen/read-noundef-metadata.rs new file mode 100644 index 00000000000..03386921c43 --- /dev/null +++ b/tests/codegen/read-noundef-metadata.rs @@ -0,0 +1,51 @@ +// compile-flags: -O -Z merge-functions=disabled +// no-system-llvm +// ignore-debug (the extra assertions get in the way) + +#![crate_type = "lib"] + +// Ensure that various forms of reading pointers correctly annotate the `load`s +// with `!noundef` metadata to enable extra optimization. The functions return +// `MaybeUninit` to keep it from being inferred from the function type. + +use std::mem::MaybeUninit; + +// CHECK-LABEL: define i8 @copy_byte( +#[no_mangle] +pub unsafe fn copy_byte(p: *const u8) -> MaybeUninit { + // CHECK-NOT: load + // CHECK: load i8, ptr %p, align 1 + // CHECK-SAME: !noundef ! + // CHECK-NOT: load + MaybeUninit::new(*p) +} + +// CHECK-LABEL: define i8 @read_byte( +#[no_mangle] +pub unsafe fn read_byte(p: *const u8) -> MaybeUninit { + // CHECK-NOT: load + // CHECK: load i8, ptr %p, align 1 + // CHECK-SAME: !noundef ! + // CHECK-NOT: load + MaybeUninit::new(p.read()) +} + +// CHECK-LABEL: define i8 @read_byte_maybe_uninit( +#[no_mangle] +pub unsafe fn read_byte_maybe_uninit(p: *const MaybeUninit) -> MaybeUninit { + // CHECK-NOT: load + // CHECK: load i8, ptr %p, align 1 + // CHECK-NOT: noundef + // CHECK-NOT: load + p.read() +} + +// CHECK-LABEL: define i8 @read_byte_assume_init( +#[no_mangle] +pub unsafe fn read_byte_assume_init(p: &MaybeUninit) -> MaybeUninit { + // CHECK-NOT: load + // CHECK: load i8, ptr %p, align 1 + // CHECK-SAME: !noundef ! + // CHECK-NOT: load + MaybeUninit::new(p.assume_init_read()) +} diff --git a/tests/mir-opt/lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff new file mode 100644 index 00000000000..27fceeedf6e --- /dev/null +++ b/tests/mir-opt/lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff @@ -0,0 +1,27 @@ +- // MIR for `read_via_copy_primitive` before LowerIntrinsics ++ // MIR for `read_via_copy_primitive` after LowerIntrinsics + + fn read_via_copy_primitive(_1: &i32) -> i32 { + debug r => _1; // in scope 0 at $DIR/lower_intrinsics.rs:+0:32: +0:33 + let mut _0: i32; // return place in scope 0 at $DIR/lower_intrinsics.rs:+0:44: +0:47 + let mut _2: *const i32; // in scope 0 at $DIR/lower_intrinsics.rs:+1:46: +1:47 + scope 1 { + } + + bb0: { + StorageLive(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47 + _2 = &raw const (*_1); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47 +- _0 = read_via_copy::(move _2) -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 +- // mir::Constant +- // + span: $DIR/lower_intrinsics.rs:85:14: 85:45 +- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const i32) -> i32 {read_via_copy::}, val: Value() } ++ _0 = (*_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 ++ goto -> bb1; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 + } + + bb1: { + StorageDead(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:47: +1:48 + return; // scope 0 at $DIR/lower_intrinsics.rs:+2:2: +2:2 + } + } + diff --git a/tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff new file mode 100644 index 00000000000..faf3f9c31b8 --- /dev/null +++ b/tests/mir-opt/lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff @@ -0,0 +1,22 @@ +- // MIR for `read_via_copy_uninhabited` before LowerIntrinsics ++ // MIR for `read_via_copy_uninhabited` after LowerIntrinsics + + fn read_via_copy_uninhabited(_1: &Never) -> Never { + debug r => _1; // in scope 0 at $DIR/lower_intrinsics.rs:+0:34: +0:35 + let mut _0: Never; // return place in scope 0 at $DIR/lower_intrinsics.rs:+0:48: +0:53 + let mut _2: *const Never; // in scope 0 at $DIR/lower_intrinsics.rs:+1:46: +1:47 + scope 1 { + } + + bb0: { + StorageLive(_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47 + _2 = &raw const (*_1); // scope 1 at $DIR/lower_intrinsics.rs:+1:46: +1:47 +- _0 = read_via_copy::(move _2); // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 +- // mir::Constant +- // + span: $DIR/lower_intrinsics.rs:90:14: 90:45 +- // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const Never) -> Never {read_via_copy::}, val: Value() } ++ _0 = (*_2); // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 ++ unreachable; // scope 1 at $DIR/lower_intrinsics.rs:+1:14: +1:48 + } + } + diff --git a/tests/mir-opt/lower_intrinsics.rs b/tests/mir-opt/lower_intrinsics.rs index 7147be43ca5..a0a1df4e5ca 100644 --- a/tests/mir-opt/lower_intrinsics.rs +++ b/tests/mir-opt/lower_intrinsics.rs @@ -79,3 +79,15 @@ pub fn with_overflow(a: i32, b: i32) { let _y = core::intrinsics::sub_with_overflow(a, b); let _z = core::intrinsics::mul_with_overflow(a, b); } + +// EMIT_MIR lower_intrinsics.read_via_copy_primitive.LowerIntrinsics.diff +pub fn read_via_copy_primitive(r: &i32) -> i32 { + unsafe { core::intrinsics::read_via_copy(r) } +} + +// EMIT_MIR lower_intrinsics.read_via_copy_uninhabited.LowerIntrinsics.diff +pub fn read_via_copy_uninhabited(r: &Never) -> Never { + unsafe { core::intrinsics::read_via_copy(r) } +} + +pub enum Never {} diff --git a/tests/ui/const-ptr/out_of_bounds_read.stderr b/tests/ui/const-ptr/out_of_bounds_read.stderr index 3e7b09a5982..89536f53f08 100644 --- a/tests/ui/const-ptr/out_of_bounds_read.stderr +++ b/tests/ui/const-ptr/out_of_bounds_read.stderr @@ -1,7 +1,7 @@ error[E0080]: evaluation of constant value failed --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL | - = note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds + = note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds | note: inside `std::ptr::read::` --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL @@ -14,7 +14,7 @@ LL | const _READ: u32 = unsafe { ptr::read(PAST_END_PTR) }; error[E0080]: evaluation of constant value failed --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL | - = note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds + = note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds | note: inside `std::ptr::read::` --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL @@ -29,7 +29,7 @@ LL | const _CONST_READ: u32 = unsafe { PAST_END_PTR.read() }; error[E0080]: evaluation of constant value failed --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL | - = note: memory access failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds + = note: dereferencing pointer failed: alloc5 has size 4, so pointer to 4 bytes starting at offset 4 is out-of-bounds | note: inside `std::ptr::read::` --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL diff --git a/tests/ui/consts/const-eval/ub-ref-ptr.stderr b/tests/ui/consts/const-eval/ub-ref-ptr.stderr index 6bd367b6469..080568b51ef 100644 --- a/tests/ui/consts/const-eval/ub-ref-ptr.stderr +++ b/tests/ui/consts/const-eval/ub-ref-ptr.stderr @@ -148,11 +148,11 @@ LL | const DATA_FN_PTR: fn() = unsafe { mem::transmute(&13) }; HEX_DUMP } -error: accessing memory with alignment 1, but alignment 4 is required +error[E0080]: evaluation of constant value failed --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL | - = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! - = note: for more information, see issue #68585 + = note: accessing memory with alignment 1, but alignment 4 is required + | note: inside `std::ptr::read::` --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL note: inside `ptr::const_ptr::::read` @@ -162,25 +162,7 @@ note: inside `UNALIGNED_READ` | LL | ptr.read(); | ^^^^^^^^^^ - = note: `#[deny(invalid_alignment)]` on by default error: aborting due to 15 previous errors For more information about this error, try `rustc --explain E0080`. -Future incompatibility report: Future breakage diagnostic: -error: accessing memory with alignment 1, but alignment 4 is required - --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL - | - = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! - = note: for more information, see issue #68585 -note: inside `std::ptr::read::` - --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL -note: inside `ptr::const_ptr::::read` - --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL -note: inside `UNALIGNED_READ` - --> $DIR/ub-ref-ptr.rs:67:5 - | -LL | ptr.read(); - | ^^^^^^^^^^ - = note: `#[deny(invalid_alignment)]` on by default - diff --git a/tests/ui/consts/issue-miri-1910.stderr b/tests/ui/consts/issue-miri-1910.stderr index 61865b1dad7..a10eea9de11 100644 --- a/tests/ui/consts/issue-miri-1910.stderr +++ b/tests/ui/consts/issue-miri-1910.stderr @@ -1,7 +1,7 @@ error[E0080]: evaluation of constant value failed --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL | - = note: unable to copy parts of a pointer from memory at ALLOC + = note: unable to turn pointer into raw bytes | = help: this code performed an operation that depends on the underlying bytes representing a pointer = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported