rustc_codegen_ssa/mir/
rvalue.rs

1use itertools::Itertools as _;
2use rustc_abi::{self as abi, FIRST_VARIANT};
3use rustc_middle::ty::adjustment::PointerCoercion;
4use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
5use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
6use rustc_middle::{bug, mir, span_bug};
7use rustc_session::config::OptLevel;
8use tracing::{debug, instrument};
9
10use super::operand::{OperandRef, OperandRefBuilder, OperandValue};
11use super::place::{PlaceRef, PlaceValue, codegen_tag_value};
12use super::{FunctionCx, LocalRef};
13use crate::common::{IntPredicate, TypeKind};
14use crate::traits::*;
15use crate::{MemFlags, base};
16
17impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
18    #[instrument(level = "trace", skip(self, bx))]
19    pub(crate) fn codegen_rvalue(
20        &mut self,
21        bx: &mut Bx,
22        dest: PlaceRef<'tcx, Bx::Value>,
23        rvalue: &mir::Rvalue<'tcx>,
24    ) {
25        match *rvalue {
26            mir::Rvalue::Use(ref operand) => {
27                let cg_operand = self.codegen_operand(bx, operand);
28                // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
29                // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
30                cg_operand.val.store(bx, dest);
31            }
32
33            mir::Rvalue::Cast(
34                mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _),
35                ref source,
36                _,
37            ) => {
38                // The destination necessarily contains a wide pointer, so if
39                // it's a scalar pair, it's a wide pointer or newtype thereof.
40                if bx.cx().is_backend_scalar_pair(dest.layout) {
41                    // Into-coerce of a thin pointer to a wide pointer -- just
42                    // use the operand path.
43                    let temp = self.codegen_rvalue_operand(bx, rvalue);
44                    temp.val.store(bx, dest);
45                    return;
46                }
47
48                // Unsize of a nontrivial struct. I would prefer for
49                // this to be eliminated by MIR building, but
50                // `CoerceUnsized` can be passed by a where-clause,
51                // so the (generic) MIR may not be able to expand it.
52                let operand = self.codegen_operand(bx, source);
53                match operand.val {
54                    OperandValue::Pair(..) | OperandValue::Immediate(_) => {
55                        // Unsize from an immediate structure. We don't
56                        // really need a temporary alloca here, but
57                        // avoiding it would require us to have
58                        // `coerce_unsized_into` use `extractvalue` to
59                        // index into the struct, and this case isn't
60                        // important enough for it.
61                        debug!("codegen_rvalue: creating ugly alloca");
62                        let scratch = PlaceRef::alloca(bx, operand.layout);
63                        scratch.storage_live(bx);
64                        operand.val.store(bx, scratch);
65                        base::coerce_unsized_into(bx, scratch, dest);
66                        scratch.storage_dead(bx);
67                    }
68                    OperandValue::Ref(val) => {
69                        if val.llextra.is_some() {
70                            bug!("unsized coercion on an unsized rvalue");
71                        }
72                        base::coerce_unsized_into(bx, val.with_type(operand.layout), dest);
73                    }
74                    OperandValue::ZeroSized => {
75                        bug!("unsized coercion on a ZST rvalue");
76                    }
77                }
78            }
79
80            mir::Rvalue::Cast(mir::CastKind::Transmute, ref operand, _ty) => {
81                let src = self.codegen_operand(bx, operand);
82                self.codegen_transmute(bx, src, dest);
83            }
84
85            mir::Rvalue::Repeat(ref elem, count) => {
86                // Do not generate the loop for zero-sized elements or empty arrays.
87                if dest.layout.is_zst() {
88                    return;
89                }
90
91                // When the element is a const with all bytes uninit, emit a single memset that
92                // writes undef to the entire destination.
93                if let mir::Operand::Constant(const_op) = elem {
94                    let val = self.eval_mir_constant(const_op);
95                    if val.all_bytes_uninit(self.cx.tcx()) {
96                        let size = bx.const_usize(dest.layout.size.bytes());
97                        bx.memset(
98                            dest.val.llval,
99                            bx.const_undef(bx.type_i8()),
100                            size,
101                            dest.val.align,
102                            MemFlags::empty(),
103                        );
104                        return;
105                    }
106                }
107
108                let cg_elem = self.codegen_operand(bx, elem);
109
110                let try_init_all_same = |bx: &mut Bx, v| {
111                    let start = dest.val.llval;
112                    let size = bx.const_usize(dest.layout.size.bytes());
113
114                    // Use llvm.memset.p0i8.* to initialize all same byte arrays
115                    if let Some(int) = bx.cx().const_to_opt_u128(v, false)
116                        && let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()]
117                        && let Ok(&byte) = bytes.iter().all_equal_value()
118                    {
119                        let fill = bx.cx().const_u8(byte);
120                        bx.memset(start, fill, size, dest.val.align, MemFlags::empty());
121                        return true;
122                    }
123
124                    // Use llvm.memset.p0i8.* to initialize byte arrays
125                    let v = bx.from_immediate(v);
126                    if bx.cx().val_ty(v) == bx.cx().type_i8() {
127                        bx.memset(start, v, size, dest.val.align, MemFlags::empty());
128                        return true;
129                    }
130                    false
131                };
132
133                if let OperandValue::Immediate(v) = cg_elem.val
134                    && try_init_all_same(bx, v)
135                {
136                    return;
137                }
138
139                let count = self
140                    .monomorphize(count)
141                    .try_to_target_usize(bx.tcx())
142                    .expect("expected monomorphic const in codegen");
143
144                bx.write_operand_repeatedly(cg_elem, count, dest);
145            }
146
147            // This implementation does field projection, so never use it for `RawPtr`,
148            // which will always be fine with the `codegen_rvalue_operand` path below.
149            mir::Rvalue::Aggregate(ref kind, ref operands)
150                if !matches!(**kind, mir::AggregateKind::RawPtr(..)) =>
151            {
152                let (variant_index, variant_dest, active_field_index) = match **kind {
153                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
154                        let variant_dest = dest.project_downcast(bx, variant_index);
155                        (variant_index, variant_dest, active_field_index)
156                    }
157                    _ => (FIRST_VARIANT, dest, None),
158                };
159                if active_field_index.is_some() {
160                    assert_eq!(operands.len(), 1);
161                }
162                for (i, operand) in operands.iter_enumerated() {
163                    let op = self.codegen_operand(bx, operand);
164                    // Do not generate stores and GEPis for zero-sized fields.
165                    if !op.layout.is_zst() {
166                        let field_index = active_field_index.unwrap_or(i);
167                        let field = if let mir::AggregateKind::Array(_) = **kind {
168                            let llindex = bx.cx().const_usize(field_index.as_u32().into());
169                            variant_dest.project_index(bx, llindex)
170                        } else {
171                            variant_dest.project_field(bx, field_index.as_usize())
172                        };
173                        op.val.store(bx, field);
174                    }
175                }
176                dest.codegen_set_discr(bx, variant_index);
177            }
178
179            _ => {
180                let temp = self.codegen_rvalue_operand(bx, rvalue);
181                temp.val.store(bx, dest);
182            }
183        }
184    }
185
186    /// Transmutes the `src` value to the destination type by writing it to `dst`.
187    ///
188    /// See also [`Self::codegen_transmute_operand`] for cases that can be done
189    /// without needing a pre-allocated place for the destination.
190    fn codegen_transmute(
191        &mut self,
192        bx: &mut Bx,
193        src: OperandRef<'tcx, Bx::Value>,
194        dst: PlaceRef<'tcx, Bx::Value>,
195    ) {
196        // The MIR validator enforces no unsized transmutes.
197        assert!(src.layout.is_sized());
198        assert!(dst.layout.is_sized());
199
200        if src.layout.size != dst.layout.size
201            || src.layout.is_uninhabited()
202            || dst.layout.is_uninhabited()
203        {
204            // These cases are all UB to actually hit, so don't emit code for them.
205            // (The size mismatches are reachable via `transmute_unchecked`.)
206            bx.unreachable_nonterminator();
207        } else {
208            // Since in this path we have a place anyway, we can store or copy to it,
209            // making sure we use the destination place's alignment even if the
210            // source would normally have a higher one.
211            src.val.store(bx, dst.val.with_type(src.layout));
212        }
213    }
214
215    /// Transmutes an `OperandValue` to another `OperandValue`.
216    ///
217    /// This is supported for all cases where the `cast` type is SSA,
218    /// but for non-ZSTs with [`abi::BackendRepr::Memory`] it ICEs.
219    pub(crate) fn codegen_transmute_operand(
220        &mut self,
221        bx: &mut Bx,
222        operand: OperandRef<'tcx, Bx::Value>,
223        cast: TyAndLayout<'tcx>,
224    ) -> OperandValue<Bx::Value> {
225        if let abi::BackendRepr::Memory { .. } = cast.backend_repr
226            && !cast.is_zst()
227        {
228            span_bug!(self.mir.span, "Use `codegen_transmute` to transmute to {cast:?}");
229        }
230
231        // `Layout` is interned, so we can do a cheap check for things that are
232        // exactly the same and thus don't need any handling.
233        if abi::Layout::eq(&operand.layout.layout, &cast.layout) {
234            return operand.val;
235        }
236
237        // Check for transmutes that are always UB.
238        if operand.layout.size != cast.size
239            || operand.layout.is_uninhabited()
240            || cast.is_uninhabited()
241        {
242            bx.unreachable_nonterminator();
243
244            // We still need to return a value of the appropriate type, but
245            // it's already UB so do the easiest thing available.
246            return OperandValue::poison(bx, cast);
247        }
248
249        // To or from pointers takes different methods, so we use this to restrict
250        // the SimdVector case to types which can be `bitcast` between each other.
251        #[inline]
252        fn vector_can_bitcast(x: abi::Scalar) -> bool {
253            matches!(
254                x,
255                abi::Scalar::Initialized {
256                    value: abi::Primitive::Int(..) | abi::Primitive::Float(..),
257                    ..
258                }
259            )
260        }
261
262        let cx = bx.cx();
263        match (operand.val, operand.layout.backend_repr, cast.backend_repr) {
264            _ if cast.is_zst() => OperandValue::ZeroSized,
265            (OperandValue::Ref(source_place_val), abi::BackendRepr::Memory { .. }, _) => {
266                assert_eq!(source_place_val.llextra, None);
267                // The existing alignment is part of `source_place_val`,
268                // so that alignment will be used, not `cast`'s.
269                bx.load_operand(source_place_val.with_type(cast)).val
270            }
271            (
272                OperandValue::Immediate(imm),
273                abi::BackendRepr::Scalar(from_scalar),
274                abi::BackendRepr::Scalar(to_scalar),
275            ) if from_scalar.size(cx) == to_scalar.size(cx) => {
276                OperandValue::Immediate(transmute_scalar(bx, imm, from_scalar, to_scalar))
277            }
278            (
279                OperandValue::Immediate(imm),
280                abi::BackendRepr::SimdVector { element: from_scalar, .. },
281                abi::BackendRepr::SimdVector { element: to_scalar, .. },
282            ) if vector_can_bitcast(from_scalar) && vector_can_bitcast(to_scalar) => {
283                let to_backend_ty = bx.cx().immediate_backend_type(cast);
284                OperandValue::Immediate(bx.bitcast(imm, to_backend_ty))
285            }
286            (
287                OperandValue::Pair(imm_a, imm_b),
288                abi::BackendRepr::ScalarPair(in_a, in_b),
289                abi::BackendRepr::ScalarPair(out_a, out_b),
290            ) if in_a.size(cx) == out_a.size(cx) && in_b.size(cx) == out_b.size(cx) => {
291                OperandValue::Pair(
292                    transmute_scalar(bx, imm_a, in_a, out_a),
293                    transmute_scalar(bx, imm_b, in_b, out_b),
294                )
295            }
296            _ => {
297                // For any other potentially-tricky cases, make a temporary instead.
298                // If anything else wants the target local to be in memory this won't
299                // be hit, as `codegen_transmute` will get called directly. Thus this
300                // is only for places where everything else wants the operand form,
301                // and thus it's not worth making those places get it from memory.
302                //
303                // Notably, Scalar ⇌ ScalarPair cases go here to avoid padding
304                // and endianness issues, as do SimdVector ones to avoid worrying
305                // about things like f32x8 ⇌ ptrx4 that would need multiple steps.
306                let align = Ord::max(operand.layout.align.abi, cast.align.abi);
307                let size = Ord::max(operand.layout.size, cast.size);
308                let temp = PlaceValue::alloca(bx, size, align);
309                bx.lifetime_start(temp.llval, size);
310                operand.val.store(bx, temp.with_type(operand.layout));
311                let val = bx.load_operand(temp.with_type(cast)).val;
312                bx.lifetime_end(temp.llval, size);
313                val
314            }
315        }
316    }
317
318    /// Cast one of the immediates from an [`OperandValue::Immediate`]
319    /// or an [`OperandValue::Pair`] to an immediate of the target type.
320    ///
321    /// Returns `None` if the cast is not possible.
322    fn cast_immediate(
323        &self,
324        bx: &mut Bx,
325        mut imm: Bx::Value,
326        from_scalar: abi::Scalar,
327        from_backend_ty: Bx::Type,
328        to_scalar: abi::Scalar,
329        to_backend_ty: Bx::Type,
330    ) -> Option<Bx::Value> {
331        use abi::Primitive::*;
332
333        // When scalars are passed by value, there's no metadata recording their
334        // valid ranges. For example, `char`s are passed as just `i32`, with no
335        // way for LLVM to know that they're 0x10FFFF at most. Thus we assume
336        // the range of the input value too, not just the output range.
337        assume_scalar_range(bx, imm, from_scalar, from_backend_ty, None);
338
339        imm = match (from_scalar.primitive(), to_scalar.primitive()) {
340            (Int(_, is_signed), Int(..)) => bx.intcast(imm, to_backend_ty, is_signed),
341            (Float(_), Float(_)) => {
342                let srcsz = bx.cx().float_width(from_backend_ty);
343                let dstsz = bx.cx().float_width(to_backend_ty);
344                if dstsz > srcsz {
345                    bx.fpext(imm, to_backend_ty)
346                } else if srcsz > dstsz {
347                    bx.fptrunc(imm, to_backend_ty)
348                } else {
349                    imm
350                }
351            }
352            (Int(_, is_signed), Float(_)) => {
353                if is_signed {
354                    bx.sitofp(imm, to_backend_ty)
355                } else {
356                    bx.uitofp(imm, to_backend_ty)
357                }
358            }
359            (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
360            (Int(_, is_signed), Pointer(..)) => {
361                let usize_imm = bx.intcast(imm, bx.cx().type_isize(), is_signed);
362                bx.inttoptr(usize_imm, to_backend_ty)
363            }
364            (Float(_), Int(_, is_signed)) => bx.cast_float_to_int(is_signed, imm, to_backend_ty),
365            _ => return None,
366        };
367        Some(imm)
368    }
369
370    pub(crate) fn codegen_rvalue_operand(
371        &mut self,
372        bx: &mut Bx,
373        rvalue: &mir::Rvalue<'tcx>,
374    ) -> OperandRef<'tcx, Bx::Value> {
375        match *rvalue {
376            mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
377                let operand = self.codegen_operand(bx, source);
378                debug!("cast operand is {:?}", operand);
379                let cast = bx.cx().layout_of(self.monomorphize(mir_cast_ty));
380
381                let val = match *kind {
382                    mir::CastKind::PointerExposeProvenance => {
383                        assert!(bx.cx().is_backend_immediate(cast));
384                        let llptr = operand.immediate();
385                        let llcast_ty = bx.cx().immediate_backend_type(cast);
386                        let lladdr = bx.ptrtoint(llptr, llcast_ty);
387                        OperandValue::Immediate(lladdr)
388                    }
389                    mir::CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
390                        match *operand.layout.ty.kind() {
391                            ty::FnDef(def_id, args) => {
392                                let instance = ty::Instance::resolve_for_fn_ptr(
393                                    bx.tcx(),
394                                    bx.typing_env(),
395                                    def_id,
396                                    args,
397                                )
398                                .unwrap();
399                                OperandValue::Immediate(bx.get_fn_addr(instance))
400                            }
401                            _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
402                        }
403                    }
404                    mir::CastKind::PointerCoercion(PointerCoercion::ClosureFnPointer(_), _) => {
405                        match *operand.layout.ty.kind() {
406                            ty::Closure(def_id, args) => {
407                                let instance = Instance::resolve_closure(
408                                    bx.cx().tcx(),
409                                    def_id,
410                                    args,
411                                    ty::ClosureKind::FnOnce,
412                                );
413                                OperandValue::Immediate(bx.cx().get_fn_addr(instance))
414                            }
415                            _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),
416                        }
417                    }
418                    mir::CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer, _) => {
419                        // This is a no-op at the LLVM level.
420                        operand.val
421                    }
422                    mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
423                        assert!(bx.cx().is_backend_scalar_pair(cast));
424                        let (lldata, llextra) = operand.val.pointer_parts();
425                        let (lldata, llextra) =
426                            base::unsize_ptr(bx, lldata, operand.layout.ty, cast.ty, llextra);
427                        OperandValue::Pair(lldata, llextra)
428                    }
429                    mir::CastKind::PointerCoercion(
430                        PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer, _
431                    ) => {
432                        bug!("{kind:?} is for borrowck, and should never appear in codegen");
433                    }
434                    mir::CastKind::PtrToPtr
435                        if bx.cx().is_backend_scalar_pair(operand.layout) =>
436                    {
437                        if let OperandValue::Pair(data_ptr, meta) = operand.val {
438                            if bx.cx().is_backend_scalar_pair(cast) {
439                                OperandValue::Pair(data_ptr, meta)
440                            } else {
441                                // Cast of wide-ptr to thin-ptr is an extraction of data-ptr.
442                                OperandValue::Immediate(data_ptr)
443                            }
444                        } else {
445                            bug!("unexpected non-pair operand");
446                        }
447                    }
448                    | mir::CastKind::IntToInt
449                    | mir::CastKind::FloatToInt
450                    | mir::CastKind::FloatToFloat
451                    | mir::CastKind::IntToFloat
452                    | mir::CastKind::PtrToPtr
453                    | mir::CastKind::FnPtrToPtr
454                    // Since int2ptr can have arbitrary integer types as input (so we have to do
455                    // sign extension and all that), it is currently best handled in the same code
456                    // path as the other integer-to-X casts.
457                    | mir::CastKind::PointerWithExposedProvenance => {
458                        let imm = operand.immediate();
459                        let abi::BackendRepr::Scalar(from_scalar) = operand.layout.backend_repr else {
460                            bug!("Found non-scalar for operand {operand:?}");
461                        };
462                        let from_backend_ty = bx.cx().immediate_backend_type(operand.layout);
463
464                        assert!(bx.cx().is_backend_immediate(cast));
465                        let to_backend_ty = bx.cx().immediate_backend_type(cast);
466                        if operand.layout.is_uninhabited() {
467                            let val = OperandValue::Immediate(bx.cx().const_poison(to_backend_ty));
468                            return OperandRef { val, layout: cast };
469                        }
470                        let abi::BackendRepr::Scalar(to_scalar) = cast.layout.backend_repr else {
471                            bug!("Found non-scalar for cast {cast:?}");
472                        };
473
474                        self.cast_immediate(bx, imm, from_scalar, from_backend_ty, to_scalar, to_backend_ty)
475                            .map(OperandValue::Immediate)
476                            .unwrap_or_else(|| {
477                                bug!("Unsupported cast of {operand:?} to {cast:?}");
478                            })
479                    }
480                    mir::CastKind::Transmute => {
481                        self.codegen_transmute_operand(bx, operand, cast)
482                    }
483                };
484                OperandRef { val, layout: cast }
485            }
486
487            mir::Rvalue::Ref(_, bk, place) => {
488                let mk_ref = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
489                    Ty::new_ref(tcx, tcx.lifetimes.re_erased, ty, bk.to_mutbl_lossy())
490                };
491                self.codegen_place_to_pointer(bx, place, mk_ref)
492            }
493
494            mir::Rvalue::CopyForDeref(place) => {
495                self.codegen_operand(bx, &mir::Operand::Copy(place))
496            }
497            mir::Rvalue::RawPtr(kind, place) => {
498                let mk_ptr = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
499                    Ty::new_ptr(tcx, ty, kind.to_mutbl_lossy())
500                };
501                self.codegen_place_to_pointer(bx, place, mk_ptr)
502            }
503
504            mir::Rvalue::Len(place) => {
505                let size = self.evaluate_array_len(bx, place);
506                OperandRef {
507                    val: OperandValue::Immediate(size),
508                    layout: bx.cx().layout_of(bx.tcx().types.usize),
509                }
510            }
511
512            mir::Rvalue::BinaryOp(op_with_overflow, box (ref lhs, ref rhs))
513                if let Some(op) = op_with_overflow.overflowing_to_wrapping() =>
514            {
515                let lhs = self.codegen_operand(bx, lhs);
516                let rhs = self.codegen_operand(bx, rhs);
517                let result = self.codegen_scalar_checked_binop(
518                    bx,
519                    op,
520                    lhs.immediate(),
521                    rhs.immediate(),
522                    lhs.layout.ty,
523                );
524                let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
525                let operand_ty = Ty::new_tup(bx.tcx(), &[val_ty, bx.tcx().types.bool]);
526                OperandRef { val: result, layout: bx.cx().layout_of(operand_ty) }
527            }
528            mir::Rvalue::BinaryOp(op, box (ref lhs, ref rhs)) => {
529                let lhs = self.codegen_operand(bx, lhs);
530                let rhs = self.codegen_operand(bx, rhs);
531                let llresult = match (lhs.val, rhs.val) {
532                    (
533                        OperandValue::Pair(lhs_addr, lhs_extra),
534                        OperandValue::Pair(rhs_addr, rhs_extra),
535                    ) => self.codegen_wide_ptr_binop(
536                        bx,
537                        op,
538                        lhs_addr,
539                        lhs_extra,
540                        rhs_addr,
541                        rhs_extra,
542                        lhs.layout.ty,
543                    ),
544
545                    (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => self
546                        .codegen_scalar_binop(
547                            bx,
548                            op,
549                            lhs_val,
550                            rhs_val,
551                            lhs.layout.ty,
552                            rhs.layout.ty,
553                        ),
554
555                    _ => bug!(),
556                };
557                OperandRef {
558                    val: OperandValue::Immediate(llresult),
559                    layout: bx.cx().layout_of(op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
560                }
561            }
562
563            mir::Rvalue::UnaryOp(op, ref operand) => {
564                let operand = self.codegen_operand(bx, operand);
565                let is_float = operand.layout.ty.is_floating_point();
566                let (val, layout) = match op {
567                    mir::UnOp::Not => {
568                        let llval = bx.not(operand.immediate());
569                        (OperandValue::Immediate(llval), operand.layout)
570                    }
571                    mir::UnOp::Neg => {
572                        let llval = if is_float {
573                            bx.fneg(operand.immediate())
574                        } else {
575                            bx.neg(operand.immediate())
576                        };
577                        (OperandValue::Immediate(llval), operand.layout)
578                    }
579                    mir::UnOp::PtrMetadata => {
580                        assert!(operand.layout.ty.is_raw_ptr() || operand.layout.ty.is_ref(),);
581                        let (_, meta) = operand.val.pointer_parts();
582                        assert_eq!(operand.layout.fields.count() > 1, meta.is_some());
583                        if let Some(meta) = meta {
584                            (OperandValue::Immediate(meta), operand.layout.field(self.cx, 1))
585                        } else {
586                            (OperandValue::ZeroSized, bx.cx().layout_of(bx.tcx().types.unit))
587                        }
588                    }
589                };
590                assert!(
591                    val.is_expected_variant_for_type(self.cx, layout),
592                    "Made wrong variant {val:?} for type {layout:?}",
593                );
594                OperandRef { val, layout }
595            }
596
597            mir::Rvalue::Discriminant(ref place) => {
598                let discr_ty = rvalue.ty(self.mir, bx.tcx());
599                let discr_ty = self.monomorphize(discr_ty);
600                let operand = self.codegen_consume(bx, place.as_ref());
601                let discr = operand.codegen_get_discr(self, bx, discr_ty);
602                OperandRef {
603                    val: OperandValue::Immediate(discr),
604                    layout: self.cx.layout_of(discr_ty),
605                }
606            }
607
608            mir::Rvalue::NullaryOp(ref null_op, ty) => {
609                let ty = self.monomorphize(ty);
610                let layout = bx.cx().layout_of(ty);
611                let val = match null_op {
612                    mir::NullOp::SizeOf => {
613                        assert!(bx.cx().type_is_sized(ty));
614                        let val = layout.size.bytes();
615                        bx.cx().const_usize(val)
616                    }
617                    mir::NullOp::AlignOf => {
618                        assert!(bx.cx().type_is_sized(ty));
619                        let val = layout.align.abi.bytes();
620                        bx.cx().const_usize(val)
621                    }
622                    mir::NullOp::OffsetOf(fields) => {
623                        let val = bx
624                            .tcx()
625                            .offset_of_subfield(bx.typing_env(), layout, fields.iter())
626                            .bytes();
627                        bx.cx().const_usize(val)
628                    }
629                    mir::NullOp::UbChecks => {
630                        let val = bx.tcx().sess.ub_checks();
631                        bx.cx().const_bool(val)
632                    }
633                    mir::NullOp::ContractChecks => {
634                        let val = bx.tcx().sess.contract_checks();
635                        bx.cx().const_bool(val)
636                    }
637                };
638                let tcx = self.cx.tcx();
639                OperandRef {
640                    val: OperandValue::Immediate(val),
641                    layout: self.cx.layout_of(null_op.ty(tcx)),
642                }
643            }
644
645            mir::Rvalue::ThreadLocalRef(def_id) => {
646                assert!(bx.cx().tcx().is_static(def_id));
647                let layout = bx.layout_of(bx.cx().tcx().static_ptr_ty(def_id, bx.typing_env()));
648                let static_ = if !def_id.is_local() && bx.cx().tcx().needs_thread_local_shim(def_id)
649                {
650                    let instance = ty::Instance {
651                        def: ty::InstanceKind::ThreadLocalShim(def_id),
652                        args: ty::GenericArgs::empty(),
653                    };
654                    let fn_ptr = bx.get_fn_addr(instance);
655                    let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
656                    let fn_ty = bx.fn_decl_backend_type(fn_abi);
657                    let fn_attrs = if bx.tcx().def_kind(instance.def_id()).has_codegen_attrs() {
658                        Some(bx.tcx().codegen_instance_attrs(instance.def))
659                    } else {
660                        None
661                    };
662                    bx.call(
663                        fn_ty,
664                        fn_attrs.as_deref(),
665                        Some(fn_abi),
666                        fn_ptr,
667                        &[],
668                        None,
669                        Some(instance),
670                    )
671                } else {
672                    bx.get_static(def_id)
673                };
674                OperandRef { val: OperandValue::Immediate(static_), layout }
675            }
676            mir::Rvalue::Use(ref operand) => self.codegen_operand(bx, operand),
677            mir::Rvalue::Repeat(ref elem, len_const) => {
678                // All arrays have `BackendRepr::Memory`, so only the ZST cases
679                // end up here. Anything else forces the destination local to be
680                // `Memory`, and thus ends up handled in `codegen_rvalue` instead.
681                let operand = self.codegen_operand(bx, elem);
682                let array_ty = Ty::new_array_with_const_len(bx.tcx(), operand.layout.ty, len_const);
683                let array_ty = self.monomorphize(array_ty);
684                let array_layout = bx.layout_of(array_ty);
685                assert!(array_layout.is_zst());
686                OperandRef { val: OperandValue::ZeroSized, layout: array_layout }
687            }
688            mir::Rvalue::Aggregate(ref kind, ref fields) => {
689                let (variant_index, active_field_index) = match **kind {
690                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
691                        (variant_index, active_field_index)
692                    }
693                    _ => (FIRST_VARIANT, None),
694                };
695
696                let ty = rvalue.ty(self.mir, self.cx.tcx());
697                let ty = self.monomorphize(ty);
698                let layout = self.cx.layout_of(ty);
699
700                let mut builder = OperandRefBuilder::new(layout);
701                for (field_idx, field) in fields.iter_enumerated() {
702                    let op = self.codegen_operand(bx, field);
703                    let fi = active_field_index.unwrap_or(field_idx);
704                    builder.insert_field(bx, variant_index, fi, op);
705                }
706
707                let tag_result = codegen_tag_value(self.cx, variant_index, layout);
708                match tag_result {
709                    Err(super::place::UninhabitedVariantError) => {
710                        // Like codegen_set_discr we use a sound abort, but could
711                        // potentially `unreachable` or just return the poison for
712                        // more optimizability, if that turns out to be helpful.
713                        bx.abort();
714                        let val = OperandValue::poison(bx, layout);
715                        OperandRef { val, layout }
716                    }
717                    Ok(maybe_tag_value) => {
718                        if let Some((tag_field, tag_imm)) = maybe_tag_value {
719                            builder.insert_imm(tag_field, tag_imm);
720                        }
721                        builder.build(bx.cx())
722                    }
723                }
724            }
725            mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
726                let operand = self.codegen_operand(bx, operand);
727                let val = operand.immediate();
728
729                let content_ty = self.monomorphize(content_ty);
730                let box_layout = bx.cx().layout_of(Ty::new_box(bx.tcx(), content_ty));
731
732                OperandRef { val: OperandValue::Immediate(val), layout: box_layout }
733            }
734            mir::Rvalue::WrapUnsafeBinder(ref operand, binder_ty) => {
735                let operand = self.codegen_operand(bx, operand);
736                let binder_ty = self.monomorphize(binder_ty);
737                let layout = bx.cx().layout_of(binder_ty);
738                OperandRef { val: operand.val, layout }
739            }
740        }
741    }
742
743    fn evaluate_array_len(&mut self, bx: &mut Bx, place: mir::Place<'tcx>) -> Bx::Value {
744        // ZST are passed as operands and require special handling
745        // because codegen_place() panics if Local is operand.
746        if let Some(index) = place.as_local()
747            && let LocalRef::Operand(op) = self.locals[index]
748            && let ty::Array(_, n) = op.layout.ty.kind()
749        {
750            let n = n.try_to_target_usize(bx.tcx()).expect("expected monomorphic const in codegen");
751            return bx.cx().const_usize(n);
752        }
753        // use common size calculation for non zero-sized types
754        let cg_value = self.codegen_place(bx, place.as_ref());
755        cg_value.len(bx.cx())
756    }
757
758    /// Codegen an `Rvalue::RawPtr` or `Rvalue::Ref`
759    fn codegen_place_to_pointer(
760        &mut self,
761        bx: &mut Bx,
762        place: mir::Place<'tcx>,
763        mk_ptr_ty: impl FnOnce(TyCtxt<'tcx>, Ty<'tcx>) -> Ty<'tcx>,
764    ) -> OperandRef<'tcx, Bx::Value> {
765        let cg_place = self.codegen_place(bx, place.as_ref());
766        let val = cg_place.val.address();
767
768        let ty = cg_place.layout.ty;
769        assert!(
770            if bx.cx().tcx().type_has_metadata(ty, bx.cx().typing_env()) {
771                matches!(val, OperandValue::Pair(..))
772            } else {
773                matches!(val, OperandValue::Immediate(..))
774            },
775            "Address of place was unexpectedly {val:?} for pointee type {ty:?}",
776        );
777
778        OperandRef { val, layout: self.cx.layout_of(mk_ptr_ty(self.cx.tcx(), ty)) }
779    }
780
781    fn codegen_scalar_binop(
782        &mut self,
783        bx: &mut Bx,
784        op: mir::BinOp,
785        lhs: Bx::Value,
786        rhs: Bx::Value,
787        lhs_ty: Ty<'tcx>,
788        rhs_ty: Ty<'tcx>,
789    ) -> Bx::Value {
790        let is_float = lhs_ty.is_floating_point();
791        let is_signed = lhs_ty.is_signed();
792        match op {
793            mir::BinOp::Add => {
794                if is_float {
795                    bx.fadd(lhs, rhs)
796                } else {
797                    bx.add(lhs, rhs)
798                }
799            }
800            mir::BinOp::AddUnchecked => {
801                if is_signed {
802                    bx.unchecked_sadd(lhs, rhs)
803                } else {
804                    bx.unchecked_uadd(lhs, rhs)
805                }
806            }
807            mir::BinOp::Sub => {
808                if is_float {
809                    bx.fsub(lhs, rhs)
810                } else {
811                    bx.sub(lhs, rhs)
812                }
813            }
814            mir::BinOp::SubUnchecked => {
815                if is_signed {
816                    bx.unchecked_ssub(lhs, rhs)
817                } else {
818                    bx.unchecked_usub(lhs, rhs)
819                }
820            }
821            mir::BinOp::Mul => {
822                if is_float {
823                    bx.fmul(lhs, rhs)
824                } else {
825                    bx.mul(lhs, rhs)
826                }
827            }
828            mir::BinOp::MulUnchecked => {
829                if is_signed {
830                    bx.unchecked_smul(lhs, rhs)
831                } else {
832                    bx.unchecked_umul(lhs, rhs)
833                }
834            }
835            mir::BinOp::Div => {
836                if is_float {
837                    bx.fdiv(lhs, rhs)
838                } else if is_signed {
839                    bx.sdiv(lhs, rhs)
840                } else {
841                    bx.udiv(lhs, rhs)
842                }
843            }
844            mir::BinOp::Rem => {
845                if is_float {
846                    bx.frem(lhs, rhs)
847                } else if is_signed {
848                    bx.srem(lhs, rhs)
849                } else {
850                    bx.urem(lhs, rhs)
851                }
852            }
853            mir::BinOp::BitOr => bx.or(lhs, rhs),
854            mir::BinOp::BitAnd => bx.and(lhs, rhs),
855            mir::BinOp::BitXor => bx.xor(lhs, rhs),
856            mir::BinOp::Offset => {
857                let pointee_type = lhs_ty
858                    .builtin_deref(true)
859                    .unwrap_or_else(|| bug!("deref of non-pointer {:?}", lhs_ty));
860                let pointee_layout = bx.cx().layout_of(pointee_type);
861                if pointee_layout.is_zst() {
862                    // `Offset` works in terms of the size of pointee,
863                    // so offsetting a pointer to ZST is a noop.
864                    lhs
865                } else {
866                    let llty = bx.cx().backend_type(pointee_layout);
867                    if !rhs_ty.is_signed() {
868                        bx.inbounds_nuw_gep(llty, lhs, &[rhs])
869                    } else {
870                        bx.inbounds_gep(llty, lhs, &[rhs])
871                    }
872                }
873            }
874            mir::BinOp::Shl | mir::BinOp::ShlUnchecked => {
875                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShlUnchecked);
876                bx.shl(lhs, rhs)
877            }
878            mir::BinOp::Shr | mir::BinOp::ShrUnchecked => {
879                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShrUnchecked);
880                if is_signed { bx.ashr(lhs, rhs) } else { bx.lshr(lhs, rhs) }
881            }
882            mir::BinOp::Ne
883            | mir::BinOp::Lt
884            | mir::BinOp::Gt
885            | mir::BinOp::Eq
886            | mir::BinOp::Le
887            | mir::BinOp::Ge => {
888                if is_float {
889                    bx.fcmp(base::bin_op_to_fcmp_predicate(op), lhs, rhs)
890                } else {
891                    bx.icmp(base::bin_op_to_icmp_predicate(op, is_signed), lhs, rhs)
892                }
893            }
894            mir::BinOp::Cmp => {
895                use std::cmp::Ordering;
896                assert!(!is_float);
897                if let Some(value) = bx.three_way_compare(lhs_ty, lhs, rhs) {
898                    return value;
899                }
900                let pred = |op| base::bin_op_to_icmp_predicate(op, is_signed);
901                if bx.cx().tcx().sess.opts.optimize == OptLevel::No {
902                    // FIXME: This actually generates tighter assembly, and is a classic trick
903                    // <https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>
904                    // However, as of 2023-11 it optimizes worse in things like derived
905                    // `PartialOrd`, so only use it in debug for now. Once LLVM can handle it
906                    // better (see <https://github.com/llvm/llvm-project/issues/73417>), it'll
907                    // be worth trying it in optimized builds as well.
908                    let is_gt = bx.icmp(pred(mir::BinOp::Gt), lhs, rhs);
909                    let gtext = bx.zext(is_gt, bx.type_i8());
910                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
911                    let ltext = bx.zext(is_lt, bx.type_i8());
912                    bx.unchecked_ssub(gtext, ltext)
913                } else {
914                    // These operations are those expected by `tests/codegen-llvm/integer-cmp.rs`,
915                    // from <https://github.com/rust-lang/rust/pull/63767>.
916                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
917                    let is_ne = bx.icmp(pred(mir::BinOp::Ne), lhs, rhs);
918                    let ge = bx.select(
919                        is_ne,
920                        bx.cx().const_i8(Ordering::Greater as i8),
921                        bx.cx().const_i8(Ordering::Equal as i8),
922                    );
923                    bx.select(is_lt, bx.cx().const_i8(Ordering::Less as i8), ge)
924                }
925            }
926            mir::BinOp::AddWithOverflow
927            | mir::BinOp::SubWithOverflow
928            | mir::BinOp::MulWithOverflow => {
929                bug!("{op:?} needs to return a pair, so call codegen_scalar_checked_binop instead")
930            }
931        }
932    }
933
934    fn codegen_wide_ptr_binop(
935        &mut self,
936        bx: &mut Bx,
937        op: mir::BinOp,
938        lhs_addr: Bx::Value,
939        lhs_extra: Bx::Value,
940        rhs_addr: Bx::Value,
941        rhs_extra: Bx::Value,
942        _input_ty: Ty<'tcx>,
943    ) -> Bx::Value {
944        match op {
945            mir::BinOp::Eq => {
946                let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
947                let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
948                bx.and(lhs, rhs)
949            }
950            mir::BinOp::Ne => {
951                let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
952                let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
953                bx.or(lhs, rhs)
954            }
955            mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
956                // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
957                let (op, strict_op) = match op {
958                    mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
959                    mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
960                    mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
961                    mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
962                    _ => bug!(),
963                };
964                let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
965                let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
966                let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
967                let rhs = bx.and(and_lhs, and_rhs);
968                bx.or(lhs, rhs)
969            }
970            _ => {
971                bug!("unexpected wide ptr binop");
972            }
973        }
974    }
975
976    fn codegen_scalar_checked_binop(
977        &mut self,
978        bx: &mut Bx,
979        op: mir::BinOp,
980        lhs: Bx::Value,
981        rhs: Bx::Value,
982        input_ty: Ty<'tcx>,
983    ) -> OperandValue<Bx::Value> {
984        let (val, of) = match op {
985            // These are checked using intrinsics
986            mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
987                let oop = match op {
988                    mir::BinOp::Add => OverflowOp::Add,
989                    mir::BinOp::Sub => OverflowOp::Sub,
990                    mir::BinOp::Mul => OverflowOp::Mul,
991                    _ => unreachable!(),
992                };
993                bx.checked_binop(oop, input_ty, lhs, rhs)
994            }
995            _ => bug!("Operator `{:?}` is not a checkable operator", op),
996        };
997
998        OperandValue::Pair(val, of)
999    }
1000}
1001
1002/// Transmutes a single scalar value `imm` from `from_scalar` to `to_scalar`.
1003///
1004/// This is expected to be in *immediate* form, as seen in [`OperandValue::Immediate`]
1005/// or [`OperandValue::Pair`] (so `i1` for bools, not `i8`, for example).
1006///
1007/// ICEs if the passed-in `imm` is not a value of the expected type for
1008/// `from_scalar`, such as if it's a vector or a pair.
1009pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
1010    bx: &mut Bx,
1011    mut imm: Bx::Value,
1012    from_scalar: abi::Scalar,
1013    to_scalar: abi::Scalar,
1014) -> Bx::Value {
1015    assert_eq!(from_scalar.size(bx.cx()), to_scalar.size(bx.cx()));
1016    let imm_ty = bx.cx().val_ty(imm);
1017    assert_ne!(
1018        bx.cx().type_kind(imm_ty),
1019        TypeKind::Vector,
1020        "Vector type {imm_ty:?} not allowed in transmute_scalar {from_scalar:?} -> {to_scalar:?}"
1021    );
1022
1023    // While optimizations will remove no-op transmutes, they might still be
1024    // there in debug or things that aren't no-op in MIR because they change
1025    // the Rust type but not the underlying layout/niche.
1026    if from_scalar == to_scalar {
1027        return imm;
1028    }
1029
1030    use abi::Primitive::*;
1031    imm = bx.from_immediate(imm);
1032
1033    let from_backend_ty = bx.cx().type_from_scalar(from_scalar);
1034    debug_assert_eq!(bx.cx().val_ty(imm), from_backend_ty);
1035    let to_backend_ty = bx.cx().type_from_scalar(to_scalar);
1036
1037    // If we have a scalar, we must already know its range. Either
1038    //
1039    // 1) It's a parameter with `range` parameter metadata,
1040    // 2) It's something we `load`ed with `!range` metadata, or
1041    // 3) After a transmute we `assume`d the range (see below).
1042    //
1043    // That said, last time we tried removing this, it didn't actually help
1044    // the rustc-perf results, so might as well keep doing it
1045    // <https://github.com/rust-lang/rust/pull/135610#issuecomment-2599275182>
1046    assume_scalar_range(bx, imm, from_scalar, from_backend_ty, Some(&to_scalar));
1047
1048    imm = match (from_scalar.primitive(), to_scalar.primitive()) {
1049        (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
1050        (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
1051        (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
1052        (Pointer(..), Int(..)) => {
1053            // FIXME: this exposes the provenance, which shouldn't be necessary.
1054            bx.ptrtoint(imm, to_backend_ty)
1055        }
1056        (Float(_), Pointer(..)) => {
1057            let int_imm = bx.bitcast(imm, bx.cx().type_isize());
1058            bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
1059        }
1060        (Pointer(..), Float(_)) => {
1061            // FIXME: this exposes the provenance, which shouldn't be necessary.
1062            let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
1063            bx.bitcast(int_imm, to_backend_ty)
1064        }
1065    };
1066
1067    debug_assert_eq!(bx.cx().val_ty(imm), to_backend_ty);
1068
1069    // This `assume` remains important for cases like (a conceptual)
1070    //    transmute::<u32, NonZeroU32>(x) == 0
1071    // since it's never passed to something with parameter metadata (especially
1072    // after MIR inlining) so the only way to tell the backend about the
1073    // constraint that the `transmute` introduced is to `assume` it.
1074    assume_scalar_range(bx, imm, to_scalar, to_backend_ty, Some(&from_scalar));
1075
1076    imm = bx.to_immediate_scalar(imm, to_scalar);
1077    imm
1078}
1079
1080/// Emits an `assume` call that `imm`'s value is within the known range of `scalar`.
1081///
1082/// If `known` is `Some`, only emits the assume if it's more specific than
1083/// whatever is already known from the range of *that* scalar.
1084fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
1085    bx: &mut Bx,
1086    imm: Bx::Value,
1087    scalar: abi::Scalar,
1088    backend_ty: Bx::Type,
1089    known: Option<&abi::Scalar>,
1090) {
1091    if matches!(bx.cx().sess().opts.optimize, OptLevel::No) {
1092        return;
1093    }
1094
1095    match (scalar, known) {
1096        (abi::Scalar::Union { .. }, _) => return,
1097        (_, None) => {
1098            if scalar.is_always_valid(bx.cx()) {
1099                return;
1100            }
1101        }
1102        (abi::Scalar::Initialized { valid_range, .. }, Some(known)) => {
1103            let known_range = known.valid_range(bx.cx());
1104            if valid_range.contains_range(known_range, scalar.size(bx.cx())) {
1105                return;
1106            }
1107        }
1108    }
1109
1110    match scalar.primitive() {
1111        abi::Primitive::Int(..) => {
1112            let range = scalar.valid_range(bx.cx());
1113            bx.assume_integer_range(imm, backend_ty, range);
1114        }
1115        abi::Primitive::Pointer(abi::AddressSpace::ZERO)
1116            if !scalar.valid_range(bx.cx()).contains(0) =>
1117        {
1118            bx.assume_nonnull(imm);
1119        }
1120        abi::Primitive::Pointer(..) | abi::Primitive::Float(..) => {}
1121    }
1122}
rustc_codegen_ssa/mir/rvalue.rs

rustc_codegen_ssa/mir/
rvalue.rs
