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