Rollup merge of rust-lang#147355 - sayantn:masked-loads, r=RalfJung,bjorn3

Add alignment parameter to `simd_masked_{load,store}` This PR adds an alignment parameter in `simd_masked_load` and `simd_masked_store`, in the form of a const-generic enum `core::intrinsics::simd::SimdAlign`. This represents the alignment of the `ptr` argument in these intrinsics as follows - `SimdAlign::Unaligned` - `ptr` is unaligned/1-byte aligned - `SimdAlign::Element` - `ptr` is aligned to the element type of the SIMD vector (default behavior in the old signature) - `SimdAlign::Vector` - `ptr` is aligned to the SIMD vector type The main motive for this is stdarch - most vector loads are either fully aligned (to the vector size) or unaligned (byte-aligned), so the previous signature doesn't cut it. Now, stdarch will mostly use `SimdAlign::Unaligned` and `SimdAlign::Vector`, whereas portable-simd will use `SimdAlign::Element`. - [x] `cg_llvm` - [x] `cg_clif` - [x] `miri`/`const_eval` ## Alternatives Using a const-generic/"const" `u32` parameter as alignment (and we error during codegen if this argument is not a power of two). This, although more flexible than this, has a few drawbacks - If we use an const-generic argument, then portable-simd somehow needs to pass `align_of::<T>()` as the alignment, which isn't possible without GCE - "const" function parameters are just an ugly hack, and a pain to deal with in non-LLVM backends We can remedy the problem with the const-generic `u32` parameter by adding a special rule for the element alignment case (e.g. `0` can mean "use the alignment of the element type), but I feel like this is not as expressive as the enum approach, although I am open to suggestions cc `@workingjubilee` `@RalfJung` `@BoxyUwU`

Author: Zalathar

compiler/rustc_codegen_cranelift/src/intrinsics/simd.rs

@@ -2,6 +2,7 @@
 
 use cranelift_codegen::ir::immediates::Offset32;
 use rustc_abi::Endian;
+use rustc_middle::ty::SimdAlign;
 
 use super::*;
 use crate::prelude::*;
@@ -960,6 +961,15 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
  let lane_clif_ty = fx.clif_type(val_lane_ty).unwrap();
  let ptr_val = ptr.load_scalar(fx);
 
+ let alignment = generic_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment();
+
+ let memflags = match alignment {
+ SimdAlign::Unaligned => MemFlags::new().with_notrap(),
+ _ => MemFlags::trusted(),
+ };
+
  for lane_idx in 0..val_lane_count {
  let val_lane = val.value_lane(fx, lane_idx).load_scalar(fx);
  let mask_lane = mask.value_lane(fx, lane_idx).load_scalar(fx);
@@ -972,7 +982,7 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
 
  fx.bcx.switch_to_block(if_enabled);
  let offset = lane_idx as i32 * lane_clif_ty.bytes() as i32;
- fx.bcx.ins().store(MemFlags::trusted(), val_lane, ptr_val, Offset32::new(offset));
+ fx.bcx.ins().store(memflags, val_lane, ptr_val, Offset32::new(offset));
  fx.bcx.ins().jump(next, &[]);
 
  fx.bcx.seal_block(next);
@@ -996,6 +1006,15 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
  let lane_clif_ty = fx.clif_type(val_lane_ty).unwrap();
  let ret_lane_layout = fx.layout_of(ret_lane_ty);
 
+ let alignment = generic_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment();
+
+ let memflags = match alignment {
+ SimdAlign::Unaligned => MemFlags::new().with_notrap(),
+ _ => MemFlags::trusted(),
+ };
+
  for lane_idx in 0..ptr_lane_count {
  let val_lane = val.value_lane(fx, lane_idx).load_scalar(fx);
  let ptr_lane = ptr.value_lane(fx, lane_idx).load_scalar(fx);
@@ -1011,7 +1030,7 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
  fx.bcx.seal_block(if_disabled);
 
  fx.bcx.switch_to_block(if_enabled);
- let res = fx.bcx.ins().load(lane_clif_ty, MemFlags::trusted(), ptr_lane, 0);
+ let res = fx.bcx.ins().load(lane_clif_ty, memflags, ptr_lane, 0);
  fx.bcx.ins().jump(next, &[res.into()]);
 
  fx.bcx.switch_to_block(if_disabled);

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -13,7 +13,7 @@ use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_hir::{self as hir};
 use rustc_middle::mir::BinOp;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, LayoutOf};
-use rustc_middle::ty::{self, GenericArgsRef, Instance, Ty, TyCtxt, TypingEnv};
+use rustc_middle::ty::{self, GenericArgsRef, Instance, SimdAlign, Ty, TyCtxt, TypingEnv};
 use rustc_middle::{bug, span_bug};
 use rustc_span::{Span, Symbol, sym};
 use rustc_symbol_mangling::{mangle_internal_symbol, symbol_name_for_instance_in_crate};
@@ -1840,15 +1840,32 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
  return Ok(call);
  }
 
+ fn llvm_alignment<'ll, 'tcx>(
+ bx: &mut Builder<'_, 'll, 'tcx>,
+ alignment: SimdAlign,
+ vector_ty: Ty<'tcx>,
+ element_ty: Ty<'tcx>,
+ ) -> u64 {
+ match alignment {
+ SimdAlign::Unaligned => 1,
+ SimdAlign::Element => bx.align_of(element_ty).bytes(),
+ SimdAlign::Vector => bx.align_of(vector_ty).bytes(),
+ }
+ }
+
  if name == sym::simd_masked_load {
- // simd_masked_load(mask: <N x i{M}>, pointer: *_ T, values: <N x T>) -> <N x T>
+ // simd_masked_load<_, _, _, const ALIGN: SimdAlign>(mask: <N x i{M}>, pointer: *_ T, values: <N x T>) -> <N x T>
  // * N: number of elements in the input vectors
  // * T: type of the element to load
  // * M: any integer width is supported, will be truncated to i1
  // Loads contiguous elements from memory behind `pointer`, but only for
  // those lanes whose `mask` bit is enabled.
  // The memory addresses corresponding to the “off” lanes are not accessed.
 
+ let alignment = fn_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment();
+
  // The element type of the "mask" argument must be a signed integer type of any width
  let mask_ty = in_ty;
  let (mask_len, mask_elem) = (in_len, in_elem);
@@ -1905,7 +1922,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
  let mask = vector_mask_to_bitmask(bx, args[0].immediate(), m_elem_bitwidth, mask_len);
 
  // Alignment of T, must be a constant integer value:
- let alignment = bx.align_of(values_elem).bytes();
+ let alignment = llvm_alignment(bx, alignment, values_ty, values_elem);
 
  let llvm_pointer = bx.type_ptr();
 
@@ -1932,14 +1949,18 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
  }
 
  if name == sym::simd_masked_store {
- // simd_masked_store(mask: <N x i{M}>, pointer: *mut T, values: <N x T>) -> ()
+ // simd_masked_store<_, _, _, const ALIGN: SimdAlign>(mask: <N x i{M}>, pointer: *mut T, values: <N x T>) -> ()
  // * N: number of elements in the input vectors
  // * T: type of the element to load
  // * M: any integer width is supported, will be truncated to i1
  // Stores contiguous elements to memory behind `pointer`, but only for
  // those lanes whose `mask` bit is enabled.
  // The memory addresses corresponding to the “off” lanes are not accessed.
 
+ let alignment = fn_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment();
+
  // The element type of the "mask" argument must be a signed integer type of any width
  let mask_ty = in_ty;
  let (mask_len, mask_elem) = (in_len, in_elem);
@@ -1990,7 +2011,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
  let mask = vector_mask_to_bitmask(bx, args[0].immediate(), m_elem_bitwidth, mask_len);
 
  // Alignment of T, must be a constant integer value:
- let alignment = bx.align_of(values_elem).bytes();
+ let alignment = llvm_alignment(bx, alignment, values_ty, values_elem);
 
  let llvm_pointer = bx.type_ptr();
 

compiler/rustc_const_eval/src/interpret/intrinsics/simd.rs

@@ -1,16 +1,16 @@
 use either::Either;
-use rustc_abi::Endian;
+use rustc_abi::{BackendRepr, Endian};
 use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::{Float, Round};
-use rustc_middle::mir::interpret::{InterpErrorKind, UndefinedBehaviorInfo};
-use rustc_middle::ty::FloatTy;
+use rustc_middle::mir::interpret::{InterpErrorKind, Pointer, UndefinedBehaviorInfo};
+use rustc_middle::ty::{FloatTy, SimdAlign};
 use rustc_middle::{bug, err_ub_format, mir, span_bug, throw_unsup_format, ty};
 use rustc_span::{Symbol, sym};
 use tracing::trace;
 
 use super::{
  ImmTy, InterpCx, InterpResult, Machine, MinMax, MulAddType, OpTy, PlaceTy, Provenance, Scalar,
- Size, interp_ok, throw_ub_format,
+ Size, TyAndLayout, assert_matches, interp_ok, throw_ub_format,
 };
 use crate::interpret::Writeable;
 
@@ -644,6 +644,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
  }
  }
  sym::simd_masked_load => {
+ let dest_layout = dest.layout;
+
  let (mask, mask_len) = self.project_to_simd(&args[0])?;
  let ptr = self.read_pointer(&args[1])?;
  let (default, default_len) = self.project_to_simd(&args[2])?;
@@ -652,6 +654,14 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
  assert_eq!(dest_len, mask_len);
  assert_eq!(dest_len, default_len);
 
+ self.check_simd_ptr_alignment(
+ ptr,
+ dest_layout,
+ generic_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment(),
+ )?;
+
  for i in 0..dest_len {
  let mask = self.read_immediate(&self.project_index(&mask, i)?)?;
  let default = self.read_immediate(&self.project_index(&default, i)?)?;
@@ -660,7 +670,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
  let val = if simd_element_to_bool(mask)? {
  // Size * u64 is implemented as always checked
  let ptr = ptr.wrapping_offset(dest.layout.size * i, self);
- let place = self.ptr_to_mplace(ptr, dest.layout);
+ // we have already checked the alignment requirements
+ let place = self.ptr_to_mplace_unaligned(ptr, dest.layout);
  self.read_immediate(&place)?
  } else {
  default
@@ -675,14 +686,23 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
  assert_eq!(mask_len, vals_len);
 
+ self.check_simd_ptr_alignment(
+ ptr,
+ args[2].layout,
+ generic_args[3].expect_const().to_value().valtree.unwrap_branch()[0]
+ .unwrap_leaf()
+ .to_simd_alignment(),
+ )?;
+
  for i in 0..vals_len {
  let mask = self.read_immediate(&self.project_index(&mask, i)?)?;
  let val = self.read_immediate(&self.project_index(&vals, i)?)?;
 
  if simd_element_to_bool(mask)? {
  // Size * u64 is implemented as always checked
  let ptr = ptr.wrapping_offset(val.layout.size * i, self);
- let place = self.ptr_to_mplace(ptr, val.layout);
+ // we have already checked the alignment requirements
+ let place = self.ptr_to_mplace_unaligned(ptr, val.layout);
  self.write_immediate(*val, &place)?
  };
  }
@@ -753,6 +773,30 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
  FloatTy::F128 => self.float_minmax::<Quad>(left, right, op)?,
  })
  }
+
+ fn check_simd_ptr_alignment(
+ &self,
+ ptr: Pointer<Option<M::Provenance>>,
+ vector_layout: TyAndLayout<'tcx>,
+ alignment: SimdAlign,
+ ) -> InterpResult<'tcx> {
+ assert_matches!(vector_layout.backend_repr, BackendRepr::SimdVector { .. });
+
+ let align = match alignment {
+ ty::SimdAlign::Unaligned => {
+ // The pointer is supposed to be unaligned, so no check is required.
+ return interp_ok(());
+ }
+ ty::SimdAlign::Element => {
+ // Take the alignment of the only field, which is an array and therefore has the same
+ // alignment as the element type.
+ vector_layout.field(self, 0).align.abi
+ }
+ ty::SimdAlign::Vector => vector_layout.align.abi,
+ };
+
+ self.check_ptr_align(ptr, align)
+ }
 }
 
 fn simd_bitmask_index(idx: u32, vec_len: u32, endianness: Endian) -> u32 {

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -695,8 +695,8 @@ pub(crate) fn check_intrinsic_type(
  (1, 0, vec![param(0), param(0), param(0)], param(0))
  }
  sym::simd_gather => (3, 0, vec![param(0), param(1), param(2)], param(0)),
- sym::simd_masked_load => (3, 0, vec![param(0), param(1), param(2)], param(2)),
- sym::simd_masked_store => (3, 0, vec![param(0), param(1), param(2)], tcx.types.unit),
+ sym::simd_masked_load => (3, 1, vec![param(0), param(1), param(2)], param(2)),
+ sym::simd_masked_store => (3, 1, vec![param(0), param(1), param(2)], tcx.types.unit),
  sym::simd_scatter => (3, 0, vec![param(0), param(1), param(2)], tcx.types.unit),
  sym::simd_insert | sym::simd_insert_dyn => {
  (2, 0, vec![param(0), tcx.types.u32, param(1)], param(0))

compiler/rustc_middle/src/ty/consts/int.rs

@@ -39,6 +39,15 @@ pub enum AtomicOrdering {
  SeqCst = 4,
 }
 
+/// An enum to represent the compiler-side view of `intrinsics::simd::SimdAlign`.
+#[derive(Debug, Copy, Clone)]
+pub enum SimdAlign {
+ // These values must match `intrinsics::simd::SimdAlign`!
+ Unaligned = 0,
+ Element = 1,
+ Vector = 2,
+}
+
 impl std::fmt::Debug for ConstInt {
  fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
  let Self { int, signed, is_ptr_sized_integral } = *self;
@@ -350,6 +359,21 @@ impl ScalarInt {
  }
  }
 
+ #[inline]
+ pub fn to_simd_alignment(self) -> SimdAlign {
+ use SimdAlign::*;
+ let val = self.to_u32();
+ if val == Unaligned as u32 {
+ Unaligned
+ } else if val == Element as u32 {
+ Element
+ } else if val == Vector as u32 {
+ Vector
+ } else {
+ panic!("not a valid simd alignment")
+ }
+ }
+
  /// Converts the `ScalarInt` to `bool`.
  /// Panics if the `size` of the `ScalarInt` is not equal to 1 byte.
  /// Errors if it is not a valid `bool`.

compiler/rustc_middle/src/ty/mod.rs

@@ -74,7 +74,7 @@ pub use self::closure::{
 };
 pub use self::consts::{
  AnonConstKind, AtomicOrdering, Const, ConstInt, ConstKind, ConstToValTreeResult, Expr,
- ExprKind, ScalarInt, UnevaluatedConst, ValTree, ValTreeKind, Value,
+ ExprKind, ScalarInt, SimdAlign, UnevaluatedConst, ValTree, ValTreeKind, Value,
 };
 pub use self::context::{
  CtxtInterners, CurrentGcx, Feed, FreeRegionInfo, GlobalCtxt, Lift, TyCtxt, TyCtxtFeed, tls,

library/core/src/intrinsics/simd.rs

@@ -2,6 +2,8 @@
 //!
 //! In this module, a "vector" is any `repr(simd)` type.
 
+use crate::marker::ConstParamTy;
+
 /// Inserts an element into a vector, returning the updated vector.
 ///
 /// `T` must be a vector with element type `U`, and `idx` must be `const`.
@@ -377,6 +379,19 @@ pub unsafe fn simd_gather<T, U, V>(val: T, ptr: U, mask: V) -> T;
 #[rustc_nounwind]
 pub unsafe fn simd_scatter<T, U, V>(val: T, ptr: U, mask: V);
 
+/// A type for alignment options for SIMD masked load/store intrinsics.
+#[derive(Debug, ConstParamTy, PartialEq, Eq)]
+pub enum SimdAlign {
+ // These values must match the compiler's `SimdAlign` defined in
+ // `rustc_middle/src/ty/consts/int.rs`!
+ /// No alignment requirements on the pointer
+ Unaligned = 0,
+ /// The pointer must be aligned to the element type of the SIMD vector
+ Element = 1,
+ /// The pointer must be aligned to the SIMD vector type
+ Vector = 2,
+}
+
 /// Reads a vector of pointers.
 ///
 /// `T` must be a vector.
@@ -392,13 +407,12 @@ pub unsafe fn simd_scatter<T, U, V>(val: T, ptr: U, mask: V);
 /// `val`.
 ///
 /// # Safety
-/// Unmasked values in `T` must be readable as if by `<ptr>::read` (e.g. aligned to the element
-/// type).
+/// `ptr` must be aligned according to the `ALIGN` parameter, see [`SimdAlign`] for details.
 ///
 /// `mask` must only contain `0` or `!0` values.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn simd_masked_load<V, U, T>(mask: V, ptr: U, val: T) -> T;
+pub unsafe fn simd_masked_load<V, U, T, const ALIGN: SimdAlign>(mask: V, ptr: U, val: T) -> T;
 
 /// Writes to a vector of pointers.
 ///
@@ -414,13 +428,12 @@ pub unsafe fn simd_masked_load<V, U, T>(mask: V, ptr: U, val: T) -> T;
 /// Otherwise if the corresponding value in `mask` is `0`, do nothing.
 ///
 /// # Safety
-/// Unmasked values in `T` must be writeable as if by `<ptr>::write` (e.g. aligned to the element
-/// type).
+/// `ptr` must be aligned according to the `ALIGN` parameter, see [`SimdAlign`] for details.
 ///
 /// `mask` must only contain `0` or `!0` values.
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn simd_masked_store<V, U, T>(mask: V, ptr: U, val: T);
+pub unsafe fn simd_masked_store<V, U, T, const ALIGN: SimdAlign>(mask: V, ptr: U, val: T);
 
 /// Adds two simd vectors elementwise, with saturation.
 ///