compiler/rustc_codegen_ssa/src/mir/operand.rs

   1 use super::place::PlaceRef;
   2 use super::{FunctionCx, LocalRef};
   3
   4 use crate::base;
   5 use crate::glue;
   6 use crate::traits::*;
   7 use crate::MemFlags;
   8
   9 use rustc_middle::mir;
  10 use rustc_middle::mir::interpret::{ConstValue, Pointer, Scalar};
  11 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
  12 use rustc_middle::ty::Ty;
  13 use rustc_target::abi::{Abi, Align, Size};
  14
  15 use std::fmt;
  16
  17 /// The representation of a Rust value. The enum variant is in fact
  18 /// uniquely determined by the value's type, but is kept as a
  19 /// safety check.
  20 #[derive(Copy, Clone, Debug)]
  21 pub enum OperandValue<V> {
  22     /// A reference to the actual operand. The data is guaranteed
  23     /// to be valid for the operand's lifetime.
  24     /// The second value, if any, is the extra data (vtable or length)
  25     /// which indicates that it refers to an unsized rvalue.
  26     Ref(V, Option<V>, Align),
  27     /// A single LLVM value.
  28     Immediate(V),
  29     /// A pair of immediate LLVM values. Used by fat pointers too.
  30     Pair(V, V),
  31 }
  32
  33 /// An `OperandRef` is an "SSA" reference to a Rust value, along with
  34 /// its type.
  35 ///
  36 /// NOTE: unless you know a value's type exactly, you should not
  37 /// generate LLVM opcodes acting on it and instead act via methods,
  38 /// to avoid nasty edge cases. In particular, using `Builder::store`
  39 /// directly is sure to cause problems -- use `OperandRef::store`
  40 /// instead.
  41 #[derive(Copy, Clone)]
  42 pub struct OperandRef<'tcx, V> {
  43     // The value.
  44     pub val: OperandValue<V>,
  45
  46     // The layout of value, based on its Rust type.
  47     pub layout: TyAndLayout<'tcx>,
  48 }
  49
  50 impl<V: CodegenObject> fmt::Debug for OperandRef<'_, V> {
  51     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  52         write!(f, "OperandRef({:?} @ {:?})", self.val, self.layout)
  53     }
  54 }
  55
  56 impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
  57     pub fn new_zst<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  58         bx: &mut Bx,
  59         layout: TyAndLayout<'tcx>,
  60     ) -> OperandRef<'tcx, V> {
  61         assert!(layout.is_zst());
  62         OperandRef {
  63             val: OperandValue::Immediate(bx.const_undef(bx.immediate_backend_type(layout))),
  64             layout,
  65         }
  66     }
  67
  68     pub fn from_const<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
  69         bx: &mut Bx,
  70         val: ConstValue<'tcx>,
  71         ty: Ty<'tcx>,
  72     ) -> Self {
  73         let layout = bx.layout_of(ty);
  74
  75         if layout.is_zst() {
  76             return OperandRef::new_zst(bx, layout);
  77         }
  78
  79         let val = match val {
  80             ConstValue::Scalar(x) => {
  81                 let Abi::Scalar(scalar) = layout.abi else {
  82                     bug!("from_const: invalid ByVal layout: {:#?}", layout);
  83                 };
  84                 let llval = bx.scalar_to_backend(x, scalar, bx.immediate_backend_type(layout));
  85                 OperandValue::Immediate(llval)
  86             }
  87             ConstValue::Slice { data, start, end } => {
  88                 let Abi::ScalarPair(a_scalar, _) = layout.abi else {
  89                     bug!("from_const: invalid ScalarPair layout: {:#?}", layout);
  90                 };
  91                 let a = Scalar::from_pointer(
  92                     Pointer::new(bx.tcx().create_memory_alloc(data), Size::from_bytes(start)),
  93                     &bx.tcx(),
  94                 );
  95                 let a_llval = bx.scalar_to_backend(
  96                     a,
  97                     a_scalar,
  98                     bx.scalar_pair_element_backend_type(layout, 0, true),
  99                 );
 100                 let b_llval = bx.const_usize((end - start) as u64);
 101                 OperandValue::Pair(a_llval, b_llval)
 102             }
 103             ConstValue::ByRef { alloc, offset } => {
 104                 return bx.load_operand(bx.from_const_alloc(layout, alloc, offset));
 105             }
 106         };
 107
 108         OperandRef { val, layout }
 109     }
 110
 111     /// Asserts that this operand refers to a scalar and returns
 112     /// a reference to its value.
 113     pub fn immediate(self) -> V {
 114         match self.val {
 115             OperandValue::Immediate(s) => s,
 116             _ => bug!("not immediate: {:?}", self),
 117         }
 118     }
 119
 120     pub fn deref<Cx: LayoutTypeMethods<'tcx>>(self, cx: &Cx) -> PlaceRef<'tcx, V> {
 121         let projected_ty = self
 122             .layout
 123             .ty
 124             .builtin_deref(true)
 125             .unwrap_or_else(|| bug!("deref of non-pointer {:?}", self))
 126             .ty;
 127         let (llptr, llextra) = match self.val {
 128             OperandValue::Immediate(llptr) => (llptr, None),
 129             OperandValue::Pair(llptr, llextra) => {
 130                 // if the box's allocator isn't a ZST, then "llextra" is actually the allocator
 131                 if self.layout.ty.is_box() && !self.layout.field(cx, 1).is_zst() {
 132                     (llptr, None)
 133                 } else {
 134                     (llptr, Some(llextra))
 135                 }
 136             }
 137             OperandValue::Ref(..) => bug!("Deref of by-Ref operand {:?}", self),
 138         };
 139         let layout = cx.layout_of(projected_ty);
 140         PlaceRef { llval: llptr, llextra, layout, align: layout.align.abi }
 141     }
 142
 143     /// If this operand is a `Pair`, we return an aggregate with the two values.
 144     /// For other cases, see `immediate`.
 145     pub fn immediate_or_packed_pair<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 146         self,
 147         bx: &mut Bx,
 148     ) -> V {
 149         if let OperandValue::Pair(a, b) = self.val {
 150             let llty = bx.cx().backend_type(self.layout);
 151             debug!("Operand::immediate_or_packed_pair: packing {:?} into {:?}", self, llty);
 152             // Reconstruct the immediate aggregate.
 153             let mut llpair = bx.cx().const_undef(llty);
 154             let imm_a = bx.from_immediate(a);
 155             let imm_b = bx.from_immediate(b);
 156             llpair = bx.insert_value(llpair, imm_a, 0);
 157             llpair = bx.insert_value(llpair, imm_b, 1);
 158             llpair
 159         } else {
 160             self.immediate()
 161         }
 162     }
 163
 164     /// If the type is a pair, we return a `Pair`, otherwise, an `Immediate`.
 165     pub fn from_immediate_or_packed_pair<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 166         bx: &mut Bx,
 167         llval: V,
 168         layout: TyAndLayout<'tcx>,
 169     ) -> Self {
 170         let val = if let Abi::ScalarPair(a, b) = layout.abi {
 171             debug!("Operand::from_immediate_or_packed_pair: unpacking {:?} @ {:?}", llval, layout);
 172
 173             // Deconstruct the immediate aggregate.
 174             let a_llval = bx.extract_value(llval, 0);
 175             let a_llval = bx.to_immediate_scalar(a_llval, a);
 176             let b_llval = bx.extract_value(llval, 1);
 177             let b_llval = bx.to_immediate_scalar(b_llval, b);
 178             OperandValue::Pair(a_llval, b_llval)
 179         } else {
 180             OperandValue::Immediate(llval)
 181         };
 182         OperandRef { val, layout }
 183     }
 184
 185     pub fn extract_field<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 186         &self,
 187         bx: &mut Bx,
 188         i: usize,
 189     ) -> Self {
 190         let field = self.layout.field(bx.cx(), i);
 191         let offset = self.layout.fields.offset(i);
 192
 193         let mut val = match (self.val, self.layout.abi) {
 194             // If the field is ZST, it has no data.
 195             _ if field.is_zst() => {
 196                 return OperandRef::new_zst(bx, field);
 197             }
 198
 199             // Newtype of a scalar, scalar pair or vector.
 200             (OperandValue::Immediate(_) | OperandValue::Pair(..), _)
 201                 if field.size == self.layout.size =>
 202             {
 203                 assert_eq!(offset.bytes(), 0);
 204                 self.val
 205             }
 206
 207             // Extract a scalar component from a pair.
 208             (OperandValue::Pair(a_llval, b_llval), Abi::ScalarPair(a, b)) => {
 209                 if offset.bytes() == 0 {
 210                     assert_eq!(field.size, a.size(bx.cx()));
 211                     OperandValue::Immediate(a_llval)
 212                 } else {
 213                     assert_eq!(offset, a.size(bx.cx()).align_to(b.align(bx.cx()).abi));
 214                     assert_eq!(field.size, b.size(bx.cx()));
 215                     OperandValue::Immediate(b_llval)
 216                 }
 217             }
 218
 219             // `#[repr(simd)]` types are also immediate.
 220             (OperandValue::Immediate(llval), Abi::Vector { .. }) => {
 221                 OperandValue::Immediate(bx.extract_element(llval, bx.cx().const_usize(i as u64)))
 222             }
 223
 224             _ => bug!("OperandRef::extract_field({:?}): not applicable", self),
 225         };
 226
 227         match (&mut val, field.abi) {
 228             (OperandValue::Immediate(llval), _) => {
 229                 // Bools in union fields needs to be truncated.
 230                 *llval = bx.to_immediate(*llval, field);
 231                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 232                 *llval = bx.bitcast(*llval, bx.cx().immediate_backend_type(field));
 233             }
 234             (OperandValue::Pair(a, b), Abi::ScalarPair(a_abi, b_abi)) => {
 235                 // Bools in union fields needs to be truncated.
 236                 *a = bx.to_immediate_scalar(*a, a_abi);
 237                 *b = bx.to_immediate_scalar(*b, b_abi);
 238                 // HACK(eddyb) have to bitcast pointers until LLVM removes pointee types.
 239                 *a = bx.bitcast(*a, bx.cx().scalar_pair_element_backend_type(field, 0, true));
 240                 *b = bx.bitcast(*b, bx.cx().scalar_pair_element_backend_type(field, 1, true));
 241             }
 242             (OperandValue::Pair(..), _) => bug!(),
 243             (OperandValue::Ref(..), _) => bug!(),
 244         }
 245
 246         OperandRef { val, layout: field }
 247     }
 248 }
 249
 250 impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
 251     pub fn store<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 252         self,
 253         bx: &mut Bx,
 254         dest: PlaceRef<'tcx, V>,
 255     ) {
 256         self.store_with_flags(bx, dest, MemFlags::empty());
 257     }
 258
 259     pub fn volatile_store<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 260         self,
 261         bx: &mut Bx,
 262         dest: PlaceRef<'tcx, V>,
 263     ) {
 264         self.store_with_flags(bx, dest, MemFlags::VOLATILE);
 265     }
 266
 267     pub fn unaligned_volatile_store<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 268         self,
 269         bx: &mut Bx,
 270         dest: PlaceRef<'tcx, V>,
 271     ) {
 272         self.store_with_flags(bx, dest, MemFlags::VOLATILE | MemFlags::UNALIGNED);
 273     }
 274
 275     pub fn nontemporal_store<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 276         self,
 277         bx: &mut Bx,
 278         dest: PlaceRef<'tcx, V>,
 279     ) {
 280         self.store_with_flags(bx, dest, MemFlags::NONTEMPORAL);
 281     }
 282
 283     fn store_with_flags<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 284         self,
 285         bx: &mut Bx,
 286         dest: PlaceRef<'tcx, V>,
 287         flags: MemFlags,
 288     ) {
 289         debug!("OperandRef::store: operand={:?}, dest={:?}", self, dest);
 290         // Avoid generating stores of zero-sized values, because the only way to have a zero-sized
 291         // value is through `undef`, and store itself is useless.
 292         if dest.layout.is_zst() {
 293             return;
 294         }
 295         match self {
 296             OperandValue::Ref(r, None, source_align) => {
 297                 if flags.contains(MemFlags::NONTEMPORAL) {
 298                     // HACK(nox): This is inefficient but there is no nontemporal memcpy.
 299                     let ty = bx.backend_type(dest.layout);
 300                     let ptr = bx.pointercast(r, bx.type_ptr_to(ty));
 301                     let val = bx.load(ty, ptr, source_align);
 302                     bx.store_with_flags(val, dest.llval, dest.align, flags);
 303                     return;
 304                 }
 305                 base::memcpy_ty(bx, dest.llval, dest.align, r, source_align, dest.layout, flags)
 306             }
 307             OperandValue::Ref(_, Some(_), _) => {
 308                 bug!("cannot directly store unsized values");
 309             }
 310             OperandValue::Immediate(s) => {
 311                 let val = bx.from_immediate(s);
 312                 bx.store_with_flags(val, dest.llval, dest.align, flags);
 313             }
 314             OperandValue::Pair(a, b) => {
 315                 let Abi::ScalarPair(a_scalar, b_scalar) = dest.layout.abi else {
 316                     bug!("store_with_flags: invalid ScalarPair layout: {:#?}", dest.layout);
 317                 };
 318                 let ty = bx.backend_type(dest.layout);
 319                 let b_offset = a_scalar.size(bx).align_to(b_scalar.align(bx).abi);
 320
 321                 let llptr = bx.struct_gep(ty, dest.llval, 0);
 322                 let val = bx.from_immediate(a);
 323                 let align = dest.align;
 324                 bx.store_with_flags(val, llptr, align, flags);
 325
 326                 let llptr = bx.struct_gep(ty, dest.llval, 1);
 327                 let val = bx.from_immediate(b);
 328                 let align = dest.align.restrict_for_offset(b_offset);
 329                 bx.store_with_flags(val, llptr, align, flags);
 330             }
 331         }
 332     }
 333
 334     pub fn store_unsized<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
 335         self,
 336         bx: &mut Bx,
 337         indirect_dest: PlaceRef<'tcx, V>,
 338     ) {
 339         debug!("OperandRef::store_unsized: operand={:?}, indirect_dest={:?}", self, indirect_dest);
 340         let flags = MemFlags::empty();
 341
 342         // `indirect_dest` must have `*mut T` type. We extract `T` out of it.
 343         let unsized_ty = indirect_dest
 344             .layout
 345             .ty
 346             .builtin_deref(true)
 347             .unwrap_or_else(|| bug!("indirect_dest has non-pointer type: {:?}", indirect_dest))
 348             .ty;
 349
 350         let OperandValue::Ref(llptr, Some(llextra), _) = self else {
 351             bug!("store_unsized called with a sized value")
 352         };
 353
 354         // FIXME: choose an appropriate alignment, or use dynamic align somehow
 355         let max_align = Align::from_bits(128).unwrap();
 356         let min_align = Align::from_bits(8).unwrap();
 357
 358         // Allocate an appropriate region on the stack, and copy the value into it
 359         let (llsize, _) = glue::size_and_align_of_dst(bx, unsized_ty, Some(llextra));
 360         let lldst = bx.array_alloca(bx.cx().type_i8(), llsize, max_align);
 361         bx.memcpy(lldst, max_align, llptr, min_align, llsize, flags);
 362
 363         // Store the allocated region and the extra to the indirect place.
 364         let indirect_operand = OperandValue::Pair(lldst, llextra);
 365         indirect_operand.store(bx, indirect_dest);
 366     }
 367 }
 368
 369 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 370     fn maybe_codegen_consume_direct(
 371         &mut self,
 372         bx: &mut Bx,
 373         place_ref: mir::PlaceRef<'tcx>,
 374     ) -> Option<OperandRef<'tcx, Bx::Value>> {
 375         debug!("maybe_codegen_consume_direct(place_ref={:?})", place_ref);
 376
 377         match self.locals[place_ref.local] {
 378             LocalRef::Operand(Some(mut o)) => {
 379                 // Moves out of scalar and scalar pair fields are trivial.
 380                 for elem in place_ref.projection.iter() {
 381                     match elem {
 382                         mir::ProjectionElem::Field(ref f, _) => {
 383                             o = o.extract_field(bx, f.index());
 384                         }
 385                         mir::ProjectionElem::Index(_)
 386                         | mir::ProjectionElem::ConstantIndex { .. } => {
 387                             // ZSTs don't require any actual memory access.
 388                             // FIXME(eddyb) deduplicate this with the identical
 389                             // checks in `codegen_consume` and `extract_field`.
 390                             let elem = o.layout.field(bx.cx(), 0);
 391                             if elem.is_zst() {
 392                                 o = OperandRef::new_zst(bx, elem);
 393                             } else {
 394                                 return None;
 395                             }
 396                         }
 397                         _ => return None,
 398                     }
 399                 }
 400
 401                 Some(o)
 402             }
 403             LocalRef::Operand(None) => {
 404                 bug!("use of {:?} before def", place_ref);
 405             }
 406             LocalRef::Place(..) | LocalRef::UnsizedPlace(..) => {
 407                 // watch out for locals that do not have an
 408                 // alloca; they are handled somewhat differently
 409                 None
 410             }
 411         }
 412     }
 413
 414     pub fn codegen_consume(
 415         &mut self,
 416         bx: &mut Bx,
 417         place_ref: mir::PlaceRef<'tcx>,
 418     ) -> OperandRef<'tcx, Bx::Value> {
 419         debug!("codegen_consume(place_ref={:?})", place_ref);
 420
 421         let ty = self.monomorphized_place_ty(place_ref);
 422         let layout = bx.cx().layout_of(ty);
 423
 424         // ZSTs don't require any actual memory access.
 425         if layout.is_zst() {
 426             return OperandRef::new_zst(bx, layout);
 427         }
 428
 429         if let Some(o) = self.maybe_codegen_consume_direct(bx, place_ref) {
 430             return o;
 431         }
 432
 433         // for most places, to consume them we just load them
 434         // out from their home
 435         let place = self.codegen_place(bx, place_ref);
 436         bx.load_operand(place)
 437     }
 438
 439     pub fn codegen_operand(
 440         &mut self,
 441         bx: &mut Bx,
 442         operand: &mir::Operand<'tcx>,
 443     ) -> OperandRef<'tcx, Bx::Value> {
 444         debug!("codegen_operand(operand={:?})", operand);
 445
 446         match *operand {
 447             mir::Operand::Copy(ref place) | mir::Operand::Move(ref place) => {
 448                 self.codegen_consume(bx, place.as_ref())
 449             }
 450
 451             mir::Operand::Constant(ref constant) => {
 452                 // This cannot fail because we checked all required_consts in advance.
 453                 self.eval_mir_constant_to_operand(bx, constant).unwrap_or_else(|_err| {
 454                     span_bug!(constant.span, "erroneous constant not captured by required_consts")
 455                 })
 456             }
 457         }
 458     }
 459 }