diff --git a/compiler/rustc_hir_typeck/src/intrinsicck.rs b/compiler/rustc_hir_typeck/src/intrinsicck.rs index 19d2befc438..eedab9fa1b0 100644 --- a/compiler/rustc_hir_typeck/src/intrinsicck.rs +++ b/compiler/rustc_hir_typeck/src/intrinsicck.rs @@ -84,6 +84,13 @@ pub fn check_transmute(&self, from: Ty<'tcx>, to: Ty<'tcx>, hir_id: HirId) { let skeleton_string = |ty: Ty<'tcx>, sk| match sk { Ok(SizeSkeleton::Known(size)) => format!("{} bits", size.bits()), Ok(SizeSkeleton::Pointer { tail, .. }) => format!("pointer to `{tail}`"), + Ok(SizeSkeleton::Generic(size)) => { + if let Some(size) = size.try_eval_target_usize(tcx, self.param_env) { + format!("{size} bytes") + } else { + format!("generic size") + } + } Err(LayoutError::Unknown(bad)) => { if bad == ty { "this type does not have a fixed size".to_owned() diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs index 42fb5d031bb..2a057e71eac 100644 --- a/compiler/rustc_middle/src/ty/layout.rs +++ b/compiler/rustc_middle/src/ty/layout.rs @@ -281,6 +281,12 @@ pub enum SizeSkeleton<'tcx> { /// Any statically computable Layout. Known(Size), + /// This is a generic const expression (i.e. N * 2), which may contain some parameters. + /// It must be of type usize, and represents the size of a type in bytes. + /// It is not required to be evaluatable to a concrete value, but can be used to check + /// that another SizeSkeleton is of equal size. + Generic(ty::Const<'tcx>), + /// A potentially-fat pointer. Pointer { /// If true, this pointer is never null. @@ -326,6 +332,35 @@ pub fn compute( ), } } + ty::Array(inner, len) if len.ty() == tcx.types.usize => { + match SizeSkeleton::compute(inner, tcx, param_env)? { + // This may succeed because the multiplication of two types may overflow + // but a single size of a nested array will not. + SizeSkeleton::Known(s) => { + if let Some(c) = len.try_eval_target_usize(tcx, param_env) { + let size = s + .bytes() + .checked_mul(c) + .ok_or_else(|| LayoutError::SizeOverflow(ty))?; + return Ok(SizeSkeleton::Known(Size::from_bytes(size))); + } + let len = tcx.expand_abstract_consts(len); + let prev = ty::Const::from_target_usize(tcx, s.bytes()); + let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, prev) else { + return Err(LayoutError::SizeOverflow(ty)); + }; + Ok(SizeSkeleton::Generic(gen_size)) + } + SizeSkeleton::Pointer { .. } => Err(err), + SizeSkeleton::Generic(g) => { + let len = tcx.expand_abstract_consts(len); + let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, g) else { + return Err(LayoutError::SizeOverflow(ty)); + }; + Ok(SizeSkeleton::Generic(gen_size)) + } + } + } ty::Adt(def, substs) => { // Only newtypes and enums w/ nullable pointer optimization. @@ -355,6 +390,9 @@ pub fn compute( } ptr = Some(field); } + SizeSkeleton::Generic(_) => { + return Err(err); + } } } Ok(ptr) @@ -410,11 +448,66 @@ pub fn same_size(self, other: SizeSkeleton<'tcx>) -> bool { (SizeSkeleton::Pointer { tail: a, .. }, SizeSkeleton::Pointer { tail: b, .. }) => { a == b } + // constants are always pre-normalized into a canonical form so this + // only needs to check if their pointers are identical. + (SizeSkeleton::Generic(a), SizeSkeleton::Generic(b)) => a == b, _ => false, } } } +/// When creating the layout for types with abstract conts in their size (i.e. [usize; 4 * N]), +/// to ensure that they have a canonical order and can be compared directly we combine all +/// constants, and sort the other terms. This allows comparison of expressions of sizes, +/// allowing for things like transmutating between types that depend on generic consts. +/// This returns `None` if multiplication of constants overflows. +fn mul_sorted_consts<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + a: ty::Const<'tcx>, + b: ty::Const<'tcx>, +) -> Option> { + use crate::mir::BinOp::Mul; + use ty::ConstKind::Expr; + use ty::Expr::Binop; + + let mut work = vec![a, b]; + let mut done = vec![]; + while let Some(n) = work.pop() { + if let Expr(Binop(Mul, l, r)) = n.kind() { + work.push(l); + work.push(r) + } else { + done.push(n); + } + } + let mut k = 1; + let mut overflow = false; + for _ in done.drain_filter(|c| { + let Some(c) = c.try_eval_target_usize(tcx, param_env) else { + return false; + }; + let Some(next) = c.checked_mul(k) else { + overflow = true; + return true; + }; + k *= next; + true + }) {} + if overflow { + return None; + } + if k != 1 { + done.push(ty::Const::from_target_usize(tcx, k)); + } else if k == 0 { + return Some(ty::Const::from_target_usize(tcx, 0)); + } + done.sort_unstable(); + + // create a single tree from the buffer + done.into_iter().reduce(|acc, n| tcx.mk_const(Expr(Binop(Mul, n, acc)), n.ty())) +} + pub trait HasTyCtxt<'tcx>: HasDataLayout { fn tcx(&self) -> TyCtxt<'tcx>; } diff --git a/tests/ui/const-generics/transmute-fail.rs b/tests/ui/const-generics/transmute-fail.rs new file mode 100644 index 00000000000..490e4de9aac --- /dev/null +++ b/tests/ui/const-generics/transmute-fail.rs @@ -0,0 +1,34 @@ +#![feature(generic_const_exprs)] +#![allow(incomplete_features)] + +fn foo(v: [[u32;H+1]; W]) -> [[u32; W+1]; H] { + unsafe { + std::mem::transmute(v) + //~^ ERROR cannot transmute + } +} + +fn bar(v: [[u32; H]; W]) -> [[u32; W]; H] { + //~^ ERROR mismatched types + //~| ERROR mismatched types + unsafe { + std::mem::transmute(v) + //~^ ERROR cannot transmute between types + } +} + +fn baz(v: [[u32; H]; W]) -> [u32; W * H * H] { + unsafe { + std::mem::transmute(v) + //~^ ERROR cannot transmute + } +} + +fn overflow(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 777777777]; 8888888] { + unsafe { + std::mem::transmute(v) + //~^ ERROR cannot transmute + } +} + +fn main() {} diff --git a/tests/ui/const-generics/transmute-fail.stderr b/tests/ui/const-generics/transmute-fail.stderr new file mode 100644 index 00000000000..bf6a3b61dbb --- /dev/null +++ b/tests/ui/const-generics/transmute-fail.stderr @@ -0,0 +1,52 @@ +error[E0512]: cannot transmute between types of different sizes, or dependently-sized types + --> $DIR/transmute-fail.rs:6:5 + | +LL | std::mem::transmute(v) + | ^^^^^^^^^^^^^^^^^^^ + | + = note: source type: `[[u32; H+1]; W]` (generic size) + = note: target type: `[[u32; W+1]; H]` (generic size) + +error[E0512]: cannot transmute between types of different sizes, or dependently-sized types + --> $DIR/transmute-fail.rs:15:5 + | +LL | std::mem::transmute(v) + | ^^^^^^^^^^^^^^^^^^^ + | + = note: source type: `[[u32; H]; W]` (this type does not have a fixed size) + = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W]) + +error[E0308]: mismatched types + --> $DIR/transmute-fail.rs:11:53 + | +LL | fn bar(v: [[u32; H]; W]) -> [[u32; W]; H] { + | ^ expected `usize`, found `bool` + +error[E0308]: mismatched types + --> $DIR/transmute-fail.rs:11:67 + | +LL | fn bar(v: [[u32; H]; W]) -> [[u32; W]; H] { + | ^ expected `usize`, found `bool` + +error[E0512]: cannot transmute between types of different sizes, or dependently-sized types + --> $DIR/transmute-fail.rs:22:5 + | +LL | std::mem::transmute(v) + | ^^^^^^^^^^^^^^^^^^^ + | + = note: source type: `[[u32; H]; W]` (generic size) + = note: target type: `[u32; W * H * H]` (generic size) + +error[E0512]: cannot transmute between types of different sizes, or dependently-sized types + --> $DIR/transmute-fail.rs:29:5 + | +LL | std::mem::transmute(v) + | ^^^^^^^^^^^^^^^^^^^ + | + = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type `[[[u32; 8888888]; 9999999]; 777777777]` are too big for the current architecture) + = note: target type: `[[[u32; 9999999]; 777777777]; 8888888]` (values of the type `[[[u32; 9999999]; 777777777]; 8888888]` are too big for the current architecture) + +error: aborting due to 6 previous errors + +Some errors have detailed explanations: E0308, E0512. +For more information about an error, try `rustc --explain E0308`. diff --git a/tests/ui/const-generics/transmute.rs b/tests/ui/const-generics/transmute.rs new file mode 100644 index 00000000000..9571b915704 --- /dev/null +++ b/tests/ui/const-generics/transmute.rs @@ -0,0 +1,82 @@ +// run-pass +#![feature(generic_const_exprs)] +#![allow(incomplete_features)] + +fn transpose(v: [[u32;H]; W]) -> [[u32; W]; H] { + unsafe { + std::mem::transmute(v) + } +} + +fn ident(v: [[u32; H]; W]) -> [[u32; H]; W] { + unsafe { + std::mem::transmute(v) + } +} + +fn flatten(v: [[u32; H]; W]) -> [u32; W * H] { + unsafe { + std::mem::transmute(v) + } +} + +fn coagulate(v: [u32; H*W]) -> [[u32; W];H] { + unsafe { + std::mem::transmute(v) + } +} + +fn flatten_3d( + v: [[[u32; D]; H]; W] +) -> [u32; D * W * H] { + unsafe { + std::mem::transmute(v) + } +} + +fn flatten_somewhat( + v: [[[u32; D]; H]; W] +) -> [[u32; D * W]; H] { + unsafe { + std::mem::transmute(v) + } +} + +fn known_size(v: [u16; L]) -> [u8; L * 2] { + unsafe { + std::mem::transmute(v) + } +} + +fn condense_bytes(v: [u8; L * 2]) -> [u16; L] { + unsafe { + std::mem::transmute(v) + } +} + +fn singleton_each(v: [u8; L]) -> [[u8;1]; L] { + unsafe { + std::mem::transmute(v) + } +} + +fn transpose_with_const( + v: [[u32; 2 * H]; W + W] +) -> [[u32; W + W]; 2 * H] { + unsafe { + std::mem::transmute(v) + } +} + +fn main() { + let _ = transpose([[0; 8]; 16]); + let _ = transpose_with_const::<8,4>([[0; 8]; 16]); + let _ = ident([[0; 8]; 16]); + let _ = flatten([[0; 13]; 5]); + let _: [[_; 5]; 13] = coagulate([0; 65]); + let _ = flatten_3d([[[0; 3]; 13]; 5]); + let _ = flatten_somewhat([[[0; 3]; 13]; 5]); + let _ = known_size([16; 13]); + let _: [u16; 5] = condense_bytes([16u8; 10]); + let _ = singleton_each([16; 10]); +}