interpret: simplify SIMD type handling

Author: RalfJung

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -384,8 +384,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             sym::simd_insert => {
                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
                 let elem = &args[2];
-                let (input, input_len) = self.operand_to_simd(&args[0])?;
-                let (dest, dest_len) = self.mplace_to_simd(dest)?;
+                let (input, input_len) = self.project_to_simd(&args[0])?;
+                let (dest, dest_len) = self.project_to_simd(dest)?;
                 assert_eq!(input_len, dest_len, "Return vector length must match input length");
                 // Bounds are not checked by typeck so we have to do it ourselves.
                 if index >= input_len {
@@ -406,7 +406,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             }
             sym::simd_extract => {
                 let index = u64::from(self.read_scalar(&args[1])?.to_u32()?);
-                let (input, input_len) = self.operand_to_simd(&args[0])?;
+                let (input, input_len) = self.project_to_simd(&args[0])?;
                 // Bounds are not checked by typeck so we have to do it ourselves.
                 if index >= input_len {
                     throw_ub_format!(

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -679,30 +679,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         Ok(str)
     }
 
-    /// Converts a repr(simd) operand into an operand where `place_index` accesses the SIMD elements.
-    /// Also returns the number of elements.
-    ///
-    /// Can (but does not always) trigger UB if `op` is uninitialized.
-    pub fn operand_to_simd(
-        &self,
-        op: &OpTy<'tcx, M::Provenance>,
-    ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::Provenance>, u64)> {
-        // Basically we just transmute this place into an array following simd_size_and_type.
-        // This only works in memory, but repr(simd) types should never be immediates anyway.
-        assert!(op.layout.ty.is_simd());
-        match op.as_mplace_or_imm() {
-            Left(mplace) => self.mplace_to_simd(&mplace),
-            Right(imm) => match *imm {
-                Immediate::Uninit => {
-                    throw_ub!(InvalidUninitBytes(None))
-                }
-                Immediate::Scalar(..) | Immediate::ScalarPair(..) => {
-                    bug!("arrays/slices can never have Scalar/ScalarPair layout")
-                }
-            },
-        }
-    }
-
     /// Read from a local of the current frame.
     /// Will not access memory, instead an indirect `Operand` is returned.
     ///

compiler/rustc_const_eval/src/interpret/place.rs

@@ -375,13 +375,15 @@ where
     Prov: Provenance,
     M: Machine<'tcx, Provenance = Prov>,
 {
-    pub fn ptr_with_meta_to_mplace(
+    fn ptr_with_meta_to_mplace(
         &self,
         ptr: Pointer<Option<M::Provenance>>,
         meta: MemPlaceMeta<M::Provenance>,
         layout: TyAndLayout<'tcx>,
+        unaligned: bool,
     ) -> MPlaceTy<'tcx, M::Provenance> {
-        let misaligned = self.is_ptr_misaligned(ptr, layout.align.abi);
+        let misaligned =
+            if unaligned { None } else { self.is_ptr_misaligned(ptr, layout.align.abi) };
         MPlaceTy { mplace: MemPlace { ptr, meta, misaligned }, layout }
     }
 
@@ -391,7 +393,16 @@ where
         layout: TyAndLayout<'tcx>,
     ) -> MPlaceTy<'tcx, M::Provenance> {
         assert!(layout.is_sized());
-        self.ptr_with_meta_to_mplace(ptr, MemPlaceMeta::None, layout)
+        self.ptr_with_meta_to_mplace(ptr, MemPlaceMeta::None, layout, /*unaligned*/ false)
+    }
+
+    pub fn ptr_to_mplace_unaligned(
+        &self,
+        ptr: Pointer<Option<M::Provenance>>,
+        layout: TyAndLayout<'tcx>,
+    ) -> MPlaceTy<'tcx, M::Provenance> {
+        assert!(layout.is_sized());
+        self.ptr_with_meta_to_mplace(ptr, MemPlaceMeta::None, layout, /*unaligned*/ true)
     }
 
     /// Take a value, which represents a (thin or wide) reference, and make it a place.
@@ -412,7 +423,7 @@ where
         // `ref_to_mplace` is called on raw pointers even if they don't actually get dereferenced;
         // we hence can't call `size_and_align_of` since that asserts more validity than we want.
         let ptr = ptr.to_pointer(self)?;
-        Ok(self.ptr_with_meta_to_mplace(ptr, meta, layout))
+        Ok(self.ptr_with_meta_to_mplace(ptr, meta, layout, /*unaligned*/ false))
     }
 
     /// Turn a mplace into a (thin or wide) mutable raw pointer, pointing to the same space.
@@ -482,23 +493,6 @@ where
         Ok(a)
     }
 
-    /// Converts a repr(simd) place into a place where `place_index` accesses the SIMD elements.
-    /// Also returns the number of elements.
-    pub fn mplace_to_simd(
-        &self,
-        mplace: &MPlaceTy<'tcx, M::Provenance>,
-    ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::Provenance>, u64)> {
-        // Basically we want to transmute this place into an array following simd_size_and_type.
-        let (len, e_ty) = mplace.layout.ty.simd_size_and_type(*self.tcx);
-        // Some SIMD types have padding, so `len` many `e_ty` does not cover the entire place.
-        // Therefore we cannot transmute, and instead we project at offset 0, which side-steps
-        // the size check.
-        let array_layout = self.layout_of(Ty::new_array(self.tcx.tcx, e_ty, len))?;
-        assert!(array_layout.size <= mplace.layout.size);
-        let mplace = mplace.offset(Size::ZERO, array_layout, self)?;
-        Ok((mplace, len))
-    }
-
     /// Turn a local in the current frame into a place.
     pub fn local_to_place(
         &self,
@@ -983,7 +977,7 @@ where
             span_bug!(self.cur_span(), "cannot allocate space for `extern` type, size is not known")
         };
         let ptr = self.allocate_ptr(size, align, kind)?;
-        Ok(self.ptr_with_meta_to_mplace(ptr.into(), meta, layout))
+        Ok(self.ptr_with_meta_to_mplace(ptr.into(), meta, layout, /*unaligned*/ false))
     }
 
     pub fn allocate(
@@ -1018,7 +1012,12 @@ where
         };
         let meta = Scalar::from_target_usize(u64::try_from(str.len()).unwrap(), self);
         let layout = self.layout_of(self.tcx.types.str_).unwrap();
-        Ok(self.ptr_with_meta_to_mplace(ptr.into(), MemPlaceMeta::Meta(meta), layout))
+        Ok(self.ptr_with_meta_to_mplace(
+            ptr.into(),
+            MemPlaceMeta::Meta(meta),
+            layout,
+            /*unaligned*/ false,
+        ))
     }
 
     pub fn raw_const_to_mplace(

compiler/rustc_const_eval/src/interpret/projection.rs

@@ -244,6 +244,19 @@ where
         base.offset(offset, field_layout, self)
     }
 
+    /// Converts a repr(simd) value into an array of the right size, such that `project_index`
+    /// accesses the SIMD elements. Also returns the number of elements.
+    pub fn project_to_simd<P: Projectable<'tcx, M::Provenance>>(
+        &self,
+        base: &P,
+    ) -> InterpResult<'tcx, (P, u64)> {
+        assert!(base.layout().ty.ty_adt_def().unwrap().repr().simd());
+        // SIMD types must be newtypes around arrays, so all we have to do is project to their only field.
+        let array = self.project_field(base, 0)?;
+        let len = array.len(self)?;
+        Ok((array, len))
+    }
+
     fn project_constant_index<P: Projectable<'tcx, M::Provenance>>(
         &self,
         base: &P,

compiler/rustc_const_eval/src/interpret/util.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty::{
 };
 use tracing::debug;
 
-use super::{throw_inval, InterpCx, MPlaceTy, MemPlaceMeta, MemoryKind};
+use super::{throw_inval, InterpCx, MPlaceTy, MemoryKind};
 use crate::const_eval::{CompileTimeInterpCx, CompileTimeMachine, InterpretationResult};
 
 /// Checks whether a type contains generic parameters which must be instantiated.
@@ -103,5 +103,5 @@ pub(crate) fn create_static_alloc<'tcx>(
     assert_eq!(ecx.machine.static_root_ids, None);
     ecx.machine.static_root_ids = Some((alloc_id, static_def_id));
     assert!(ecx.memory.alloc_map.insert(alloc_id, (MemoryKind::Stack, alloc)).is_none());
-    Ok(ecx.ptr_with_meta_to_mplace(Pointer::from(alloc_id).into(), MemPlaceMeta::None, layout))
+    Ok(ecx.ptr_to_mplace(Pointer::from(alloc_id).into(), layout))
 }

src/tools/miri/src/intrinsics/simd.rs

@@ -50,8 +50,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             | "bitreverse"
             => {
                 let [op] = check_arg_count(args)?;
-                let (op, op_len) = this.operand_to_simd(op)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (op, op_len) = this.project_to_simd(op)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, op_len);
 
@@ -200,9 +200,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 use mir::BinOp;
 
                 let [left, right] = check_arg_count(args)?;
-                let (left, left_len) = this.operand_to_simd(left)?;
-                let (right, right_len) = this.operand_to_simd(right)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (left, left_len) = this.project_to_simd(left)?;
+                let (right, right_len) = this.project_to_simd(right)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, left_len);
                 assert_eq!(dest_len, right_len);
@@ -291,10 +291,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "fma" => {
                 let [a, b, c] = check_arg_count(args)?;
-                let (a, a_len) = this.operand_to_simd(a)?;
-                let (b, b_len) = this.operand_to_simd(b)?;
-                let (c, c_len) = this.operand_to_simd(c)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (a, a_len) = this.project_to_simd(a)?;
+                let (b, b_len) = this.project_to_simd(b)?;
+                let (c, c_len) = this.project_to_simd(c)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, a_len);
                 assert_eq!(dest_len, b_len);
@@ -345,7 +345,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 use mir::BinOp;
 
                 let [op] = check_arg_count(args)?;
-                let (op, op_len) = this.operand_to_simd(op)?;
+                let (op, op_len) = this.project_to_simd(op)?;
 
                 let imm_from_bool =
                     |b| ImmTy::from_scalar(Scalar::from_bool(b), this.machine.layouts.bool);
@@ -408,7 +408,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 use mir::BinOp;
 
                 let [op, init] = check_arg_count(args)?;
-                let (op, op_len) = this.operand_to_simd(op)?;
+                let (op, op_len) = this.project_to_simd(op)?;
                 let init = this.read_immediate(init)?;
 
                 let mir_op = match intrinsic_name {
@@ -426,10 +426,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "select" => {
                 let [mask, yes, no] = check_arg_count(args)?;
-                let (mask, mask_len) = this.operand_to_simd(mask)?;
-                let (yes, yes_len) = this.operand_to_simd(yes)?;
-                let (no, no_len) = this.operand_to_simd(no)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (mask, mask_len) = this.project_to_simd(mask)?;
+                let (yes, yes_len) = this.project_to_simd(yes)?;
+                let (no, no_len) = this.project_to_simd(no)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, mask_len);
                 assert_eq!(dest_len, yes_len);
@@ -448,9 +448,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             // Variant of `select` that takes a bitmask rather than a "vector of bool".
             "select_bitmask" => {
                 let [mask, yes, no] = check_arg_count(args)?;
-                let (yes, yes_len) = this.operand_to_simd(yes)?;
-                let (no, no_len) = this.operand_to_simd(no)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (yes, yes_len) = this.project_to_simd(yes)?;
+                let (no, no_len) = this.project_to_simd(no)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
                 let bitmask_len = dest_len.next_multiple_of(8);
                 if bitmask_len > 64 {
                     throw_unsup_format!(
@@ -522,7 +522,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             // Converts a "vector of bool" into a bitmask.
             "bitmask" => {
                 let [op] = check_arg_count(args)?;
-                let (op, op_len) = this.operand_to_simd(op)?;
+                let (op, op_len) = this.project_to_simd(op)?;
                 let bitmask_len = op_len.next_multiple_of(8);
                 if bitmask_len > 64 {
                     throw_unsup_format!(
@@ -570,8 +570,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "cast" | "as" | "cast_ptr" | "expose_provenance" | "with_exposed_provenance" => {
                 let [op] = check_arg_count(args)?;
-                let (op, op_len) = this.operand_to_simd(op)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (op, op_len) = this.project_to_simd(op)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, op_len);
 
@@ -627,9 +627,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "shuffle_generic" => {
                 let [left, right] = check_arg_count(args)?;
-                let (left, left_len) = this.operand_to_simd(left)?;
-                let (right, right_len) = this.operand_to_simd(right)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (left, left_len) = this.project_to_simd(left)?;
+                let (right, right_len) = this.project_to_simd(right)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 let index = generic_args[2]
                     .expect_const()
@@ -662,9 +662,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "shuffle" => {
                 let [left, right, index] = check_arg_count(args)?;
-                let (left, left_len) = this.operand_to_simd(left)?;
-                let (right, right_len) = this.operand_to_simd(right)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (left, left_len) = this.project_to_simd(left)?;
+                let (right, right_len) = this.project_to_simd(right)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 // `index` is an array, not a SIMD type
                 let ty::Array(_, index_len) = index.layout.ty.kind() else {
@@ -702,10 +702,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "gather" => {
                 let [passthru, ptrs, mask] = check_arg_count(args)?;
-                let (passthru, passthru_len) = this.operand_to_simd(passthru)?;
-                let (ptrs, ptrs_len) = this.operand_to_simd(ptrs)?;
-                let (mask, mask_len) = this.operand_to_simd(mask)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (passthru, passthru_len) = this.project_to_simd(passthru)?;
+                let (ptrs, ptrs_len) = this.project_to_simd(ptrs)?;
+                let (mask, mask_len) = this.project_to_simd(mask)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, passthru_len);
                 assert_eq!(dest_len, ptrs_len);
@@ -728,9 +728,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "scatter" => {
                 let [value, ptrs, mask] = check_arg_count(args)?;
-                let (value, value_len) = this.operand_to_simd(value)?;
-                let (ptrs, ptrs_len) = this.operand_to_simd(ptrs)?;
-                let (mask, mask_len) = this.operand_to_simd(mask)?;
+                let (value, value_len) = this.project_to_simd(value)?;
+                let (ptrs, ptrs_len) = this.project_to_simd(ptrs)?;
+                let (mask, mask_len) = this.project_to_simd(mask)?;
 
                 assert_eq!(ptrs_len, value_len);
                 assert_eq!(ptrs_len, mask_len);
@@ -748,10 +748,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "masked_load" => {
                 let [mask, ptr, default] = check_arg_count(args)?;
-                let (mask, mask_len) = this.operand_to_simd(mask)?;
+                let (mask, mask_len) = this.project_to_simd(mask)?;
                 let ptr = this.read_pointer(ptr)?;
-                let (default, default_len) = this.operand_to_simd(default)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (default, default_len) = this.project_to_simd(default)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, mask_len);
                 assert_eq!(dest_len, default_len);
@@ -775,9 +775,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
             "masked_store" => {
                 let [mask, ptr, vals] = check_arg_count(args)?;
-                let (mask, mask_len) = this.operand_to_simd(mask)?;
+                let (mask, mask_len) = this.project_to_simd(mask)?;
                 let ptr = this.read_pointer(ptr)?;
-                let (vals, vals_len) = this.operand_to_simd(vals)?;
+                let (vals, vals_len) = this.project_to_simd(vals)?;
 
                 assert_eq!(mask_len, vals_len);
 

src/tools/miri/src/shims/foreign_items.rs

@@ -903,8 +903,8 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
             name if name.starts_with("llvm.ctpop.v") => {
                 let [op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 
-                let (op, op_len) = this.operand_to_simd(op)?;
-                let (dest, dest_len) = this.mplace_to_simd(dest)?;
+                let (op, op_len) = this.project_to_simd(op)?;
+                let (dest, dest_len) = this.project_to_simd(dest)?;
 
                 assert_eq!(dest_len, op_len);