rustc_codegen_ssa/mir/
rvalue.rs

1use rustc_abi::{self as abi, FIRST_VARIANT};
2use rustc_middle::ty::adjustment::PointerCoercion;
3use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
4use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
5use rustc_middle::{bug, mir};
6use rustc_session::config::OptLevel;
7use tracing::{debug, instrument};
8
9use super::operand::{OperandRef, OperandRefBuilder, OperandValue};
10use super::place::{PlaceRef, codegen_tag_value};
11use super::{FunctionCx, LocalRef};
12use crate::common::{IntPredicate, TypeKind};
13use crate::traits::*;
14use crate::{MemFlags, base};
15
16impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
17    #[instrument(level = "trace", skip(self, bx))]
18    pub(crate) fn codegen_rvalue(
19        &mut self,
20        bx: &mut Bx,
21        dest: PlaceRef<'tcx, Bx::Value>,
22        rvalue: &mir::Rvalue<'tcx>,
23    ) {
24        match *rvalue {
25            mir::Rvalue::Use(ref operand) => {
26                let cg_operand = self.codegen_operand(bx, operand);
27                // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
28                // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
29                cg_operand.val.store(bx, dest);
30            }
31
32            mir::Rvalue::Cast(
33                mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _),
34                ref source,
35                _,
36            ) => {
37                // The destination necessarily contains a wide pointer, so if
38                // it's a scalar pair, it's a wide pointer or newtype thereof.
39                if bx.cx().is_backend_scalar_pair(dest.layout) {
40                    // Into-coerce of a thin pointer to a wide pointer -- just
41                    // use the operand path.
42                    let temp = self.codegen_rvalue_operand(bx, rvalue);
43                    temp.val.store(bx, dest);
44                    return;
45                }
46
47                // Unsize of a nontrivial struct. I would prefer for
48                // this to be eliminated by MIR building, but
49                // `CoerceUnsized` can be passed by a where-clause,
50                // so the (generic) MIR may not be able to expand it.
51                let operand = self.codegen_operand(bx, source);
52                match operand.val {
53                    OperandValue::Pair(..) | OperandValue::Immediate(_) => {
54                        // Unsize from an immediate structure. We don't
55                        // really need a temporary alloca here, but
56                        // avoiding it would require us to have
57                        // `coerce_unsized_into` use `extractvalue` to
58                        // index into the struct, and this case isn't
59                        // important enough for it.
60                        debug!("codegen_rvalue: creating ugly alloca");
61                        let scratch = PlaceRef::alloca(bx, operand.layout);
62                        scratch.storage_live(bx);
63                        operand.val.store(bx, scratch);
64                        base::coerce_unsized_into(bx, scratch, dest);
65                        scratch.storage_dead(bx);
66                    }
67                    OperandValue::Ref(val) => {
68                        if val.llextra.is_some() {
69                            bug!("unsized coercion on an unsized rvalue");
70                        }
71                        base::coerce_unsized_into(bx, val.with_type(operand.layout), dest);
72                    }
73                    OperandValue::ZeroSized => {
74                        bug!("unsized coercion on a ZST rvalue");
75                    }
76                }
77            }
78
79            mir::Rvalue::Cast(mir::CastKind::Transmute, ref operand, _ty) => {
80                let src = self.codegen_operand(bx, operand);
81                self.codegen_transmute(bx, src, dest);
82            }
83
84            mir::Rvalue::Repeat(ref elem, count) => {
85                // Do not generate the loop for zero-sized elements or empty arrays.
86                if dest.layout.is_zst() {
87                    return;
88                }
89
90                // When the element is a const with all bytes uninit, emit a single memset that
91                // writes undef to the entire destination.
92                if let mir::Operand::Constant(const_op) = elem {
93                    let val = self.eval_mir_constant(const_op);
94                    if val.all_bytes_uninit(self.cx.tcx()) {
95                        let size = bx.const_usize(dest.layout.size.bytes());
96                        bx.memset(
97                            dest.val.llval,
98                            bx.const_undef(bx.type_i8()),
99                            size,
100                            dest.val.align,
101                            MemFlags::empty(),
102                        );
103                        return;
104                    }
105                }
106
107                let cg_elem = self.codegen_operand(bx, elem);
108
109                let try_init_all_same = |bx: &mut Bx, v| {
110                    let start = dest.val.llval;
111                    let size = bx.const_usize(dest.layout.size.bytes());
112
113                    // Use llvm.memset.p0i8.* to initialize all same byte arrays
114                    if let Some(int) = bx.cx().const_to_opt_u128(v, false) {
115                        let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()];
116                        let first = bytes[0];
117                        if bytes[1..].iter().all(|&b| b == first) {
118                            let fill = bx.cx().const_u8(first);
119                            bx.memset(start, fill, size, dest.val.align, MemFlags::empty());
120                            return true;
121                        }
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                match cg_elem.val {
134                    OperandValue::Immediate(v) => {
135                        if try_init_all_same(bx, v) {
136                            return;
137                        }
138                    }
139                    _ => (),
140                }
141
142                let count = self
143                    .monomorphize(count)
144                    .try_to_target_usize(bx.tcx())
145                    .expect("expected monomorphic const in codegen");
146
147                bx.write_operand_repeatedly(cg_elem, count, dest);
148            }
149
150            // This implementation does field projection, so never use it for `RawPtr`,
151            // which will always be fine with the `codegen_rvalue_operand` path below.
152            mir::Rvalue::Aggregate(ref kind, ref operands)
153                if !matches!(**kind, mir::AggregateKind::RawPtr(..)) =>
154            {
155                let (variant_index, variant_dest, active_field_index) = match **kind {
156                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
157                        let variant_dest = dest.project_downcast(bx, variant_index);
158                        (variant_index, variant_dest, active_field_index)
159                    }
160                    _ => (FIRST_VARIANT, dest, None),
161                };
162                if active_field_index.is_some() {
163                    assert_eq!(operands.len(), 1);
164                }
165                for (i, operand) in operands.iter_enumerated() {
166                    let op = self.codegen_operand(bx, operand);
167                    // Do not generate stores and GEPis for zero-sized fields.
168                    if !op.layout.is_zst() {
169                        let field_index = active_field_index.unwrap_or(i);
170                        let field = if let mir::AggregateKind::Array(_) = **kind {
171                            let llindex = bx.cx().const_usize(field_index.as_u32().into());
172                            variant_dest.project_index(bx, llindex)
173                        } else {
174                            variant_dest.project_field(bx, field_index.as_usize())
175                        };
176                        op.val.store(bx, field);
177                    }
178                }
179                dest.codegen_set_discr(bx, variant_index);
180            }
181
182            _ => {
183                assert!(self.rvalue_creates_operand(rvalue));
184                let temp = self.codegen_rvalue_operand(bx, rvalue);
185                temp.val.store(bx, dest);
186            }
187        }
188    }
189
190    /// Transmutes the `src` value to the destination type by writing it to `dst`.
191    ///
192    /// See also [`Self::codegen_transmute_operand`] for cases that can be done
193    /// without needing a pre-allocated place for the destination.
194    fn codegen_transmute(
195        &mut self,
196        bx: &mut Bx,
197        src: OperandRef<'tcx, Bx::Value>,
198        dst: PlaceRef<'tcx, Bx::Value>,
199    ) {
200        // The MIR validator enforces no unsized transmutes.
201        assert!(src.layout.is_sized());
202        assert!(dst.layout.is_sized());
203
204        if src.layout.size != dst.layout.size
205            || src.layout.is_uninhabited()
206            || dst.layout.is_uninhabited()
207        {
208            // These cases are all UB to actually hit, so don't emit code for them.
209            // (The size mismatches are reachable via `transmute_unchecked`.)
210            bx.unreachable_nonterminator();
211        } else {
212            // Since in this path we have a place anyway, we can store or copy to it,
213            // making sure we use the destination place's alignment even if the
214            // source would normally have a higher one.
215            src.val.store(bx, dst.val.with_type(src.layout));
216        }
217    }
218
219    /// Transmutes an `OperandValue` to another `OperandValue`.
220    ///
221    /// This is supported only for cases where [`Self::rvalue_creates_operand`]
222    /// returns `true`, and will ICE otherwise. (In particular, anything that
223    /// would need to `alloca` in order to return a `PlaceValue` will ICE,
224    /// expecting those to go via [`Self::codegen_transmute`] instead where
225    /// the destination place is already allocated.)
226    pub(crate) fn codegen_transmute_operand(
227        &mut self,
228        bx: &mut Bx,
229        operand: OperandRef<'tcx, Bx::Value>,
230        cast: TyAndLayout<'tcx>,
231    ) -> OperandValue<Bx::Value> {
232        // Check for transmutes that are always UB.
233        if operand.layout.size != cast.size
234            || operand.layout.is_uninhabited()
235            || cast.is_uninhabited()
236        {
237            bx.unreachable_nonterminator();
238
239            // We still need to return a value of the appropriate type, but
240            // it's already UB so do the easiest thing available.
241            return OperandValue::poison(bx, cast);
242        }
243
244        match (operand.val, operand.layout.backend_repr, cast.backend_repr) {
245            _ if cast.is_zst() => OperandValue::ZeroSized,
246            (_, _, abi::BackendRepr::Memory { .. }) => {
247                bug!("Cannot `codegen_transmute_operand` to non-ZST memory-ABI output {cast:?}");
248            }
249            (OperandValue::Ref(source_place_val), abi::BackendRepr::Memory { .. }, _) => {
250                assert_eq!(source_place_val.llextra, None);
251                // The existing alignment is part of `source_place_val`,
252                // so that alignment will be used, not `cast`'s.
253                bx.load_operand(source_place_val.with_type(cast)).val
254            }
255            (
256                OperandValue::Immediate(imm),
257                abi::BackendRepr::Scalar(from_scalar),
258                abi::BackendRepr::Scalar(to_scalar),
259            ) => OperandValue::Immediate(transmute_scalar(bx, imm, from_scalar, to_scalar)),
260            (
261                OperandValue::Pair(imm_a, imm_b),
262                abi::BackendRepr::ScalarPair(in_a, in_b),
263                abi::BackendRepr::ScalarPair(out_a, out_b),
264            ) => OperandValue::Pair(
265                transmute_scalar(bx, imm_a, in_a, out_a),
266                transmute_scalar(bx, imm_b, in_b, out_b),
267            ),
268            _ => bug!("Cannot `codegen_transmute_operand` {operand:?} to {cast:?}"),
269        }
270    }
271
272    /// Cast one of the immediates from an [`OperandValue::Immediate`]
273    /// or an [`OperandValue::Pair`] to an immediate of the target type.
274    ///
275    /// Returns `None` if the cast is not possible.
276    fn cast_immediate(
277        &self,
278        bx: &mut Bx,
279        mut imm: Bx::Value,
280        from_scalar: abi::Scalar,
281        from_backend_ty: Bx::Type,
282        to_scalar: abi::Scalar,
283        to_backend_ty: Bx::Type,
284    ) -> Option<Bx::Value> {
285        use abi::Primitive::*;
286
287        // When scalars are passed by value, there's no metadata recording their
288        // valid ranges. For example, `char`s are passed as just `i32`, with no
289        // way for LLVM to know that they're 0x10FFFF at most. Thus we assume
290        // the range of the input value too, not just the output range.
291        assume_scalar_range(bx, imm, from_scalar, from_backend_ty);
292
293        imm = match (from_scalar.primitive(), to_scalar.primitive()) {
294            (Int(_, is_signed), Int(..)) => bx.intcast(imm, to_backend_ty, is_signed),
295            (Float(_), Float(_)) => {
296                let srcsz = bx.cx().float_width(from_backend_ty);
297                let dstsz = bx.cx().float_width(to_backend_ty);
298                if dstsz > srcsz {
299                    bx.fpext(imm, to_backend_ty)
300                } else if srcsz > dstsz {
301                    bx.fptrunc(imm, to_backend_ty)
302                } else {
303                    imm
304                }
305            }
306            (Int(_, is_signed), Float(_)) => {
307                if is_signed {
308                    bx.sitofp(imm, to_backend_ty)
309                } else {
310                    bx.uitofp(imm, to_backend_ty)
311                }
312            }
313            (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
314            (Int(_, is_signed), Pointer(..)) => {
315                let usize_imm = bx.intcast(imm, bx.cx().type_isize(), is_signed);
316                bx.inttoptr(usize_imm, to_backend_ty)
317            }
318            (Float(_), Int(_, is_signed)) => bx.cast_float_to_int(is_signed, imm, to_backend_ty),
319            _ => return None,
320        };
321        Some(imm)
322    }
323
324    pub(crate) fn codegen_rvalue_operand(
325        &mut self,
326        bx: &mut Bx,
327        rvalue: &mir::Rvalue<'tcx>,
328    ) -> OperandRef<'tcx, Bx::Value> {
329        assert!(self.rvalue_creates_operand(rvalue), "cannot codegen {rvalue:?} to operand",);
330
331        match *rvalue {
332            mir::Rvalue::Cast(ref kind, ref source, mir_cast_ty) => {
333                let operand = self.codegen_operand(bx, source);
334                debug!("cast operand is {:?}", operand);
335                let cast = bx.cx().layout_of(self.monomorphize(mir_cast_ty));
336
337                let val = match *kind {
338                    mir::CastKind::PointerExposeProvenance => {
339                        assert!(bx.cx().is_backend_immediate(cast));
340                        let llptr = operand.immediate();
341                        let llcast_ty = bx.cx().immediate_backend_type(cast);
342                        let lladdr = bx.ptrtoint(llptr, llcast_ty);
343                        OperandValue::Immediate(lladdr)
344                    }
345                    mir::CastKind::PointerCoercion(PointerCoercion::ReifyFnPointer, _) => {
346                        match *operand.layout.ty.kind() {
347                            ty::FnDef(def_id, args) => {
348                                let instance = ty::Instance::resolve_for_fn_ptr(
349                                    bx.tcx(),
350                                    bx.typing_env(),
351                                    def_id,
352                                    args,
353                                )
354                                .unwrap();
355                                OperandValue::Immediate(bx.get_fn_addr(instance))
356                            }
357                            _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
358                        }
359                    }
360                    mir::CastKind::PointerCoercion(PointerCoercion::ClosureFnPointer(_), _) => {
361                        match *operand.layout.ty.kind() {
362                            ty::Closure(def_id, args) => {
363                                let instance = Instance::resolve_closure(
364                                    bx.cx().tcx(),
365                                    def_id,
366                                    args,
367                                    ty::ClosureKind::FnOnce,
368                                );
369                                OperandValue::Immediate(bx.cx().get_fn_addr(instance))
370                            }
371                            _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),
372                        }
373                    }
374                    mir::CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer, _) => {
375                        // This is a no-op at the LLVM level.
376                        operand.val
377                    }
378                    mir::CastKind::PointerCoercion(PointerCoercion::Unsize, _) => {
379                        assert!(bx.cx().is_backend_scalar_pair(cast));
380                        let (lldata, llextra) = operand.val.pointer_parts();
381                        let (lldata, llextra) =
382                            base::unsize_ptr(bx, lldata, operand.layout.ty, cast.ty, llextra);
383                        OperandValue::Pair(lldata, llextra)
384                    }
385                    mir::CastKind::PointerCoercion(
386                        PointerCoercion::MutToConstPointer | PointerCoercion::ArrayToPointer, _
387                    ) => {
388                        bug!("{kind:?} is for borrowck, and should never appear in codegen");
389                    }
390                    mir::CastKind::PtrToPtr
391                        if bx.cx().is_backend_scalar_pair(operand.layout) =>
392                    {
393                        if let OperandValue::Pair(data_ptr, meta) = operand.val {
394                            if bx.cx().is_backend_scalar_pair(cast) {
395                                OperandValue::Pair(data_ptr, meta)
396                            } else {
397                                // Cast of wide-ptr to thin-ptr is an extraction of data-ptr.
398                                OperandValue::Immediate(data_ptr)
399                            }
400                        } else {
401                            bug!("unexpected non-pair operand");
402                        }
403                    }
404                    | mir::CastKind::IntToInt
405                    | mir::CastKind::FloatToInt
406                    | mir::CastKind::FloatToFloat
407                    | mir::CastKind::IntToFloat
408                    | mir::CastKind::PtrToPtr
409                    | mir::CastKind::FnPtrToPtr
410                    // Since int2ptr can have arbitrary integer types as input (so we have to do
411                    // sign extension and all that), it is currently best handled in the same code
412                    // path as the other integer-to-X casts.
413                    | mir::CastKind::PointerWithExposedProvenance => {
414                        let imm = operand.immediate();
415                        let abi::BackendRepr::Scalar(from_scalar) = operand.layout.backend_repr else {
416                            bug!("Found non-scalar for operand {operand:?}");
417                        };
418                        let from_backend_ty = bx.cx().immediate_backend_type(operand.layout);
419
420                        assert!(bx.cx().is_backend_immediate(cast));
421                        let to_backend_ty = bx.cx().immediate_backend_type(cast);
422                        if operand.layout.is_uninhabited() {
423                            let val = OperandValue::Immediate(bx.cx().const_poison(to_backend_ty));
424                            return OperandRef { val, layout: cast };
425                        }
426                        let abi::BackendRepr::Scalar(to_scalar) = cast.layout.backend_repr else {
427                            bug!("Found non-scalar for cast {cast:?}");
428                        };
429
430                        self.cast_immediate(bx, imm, from_scalar, from_backend_ty, to_scalar, to_backend_ty)
431                            .map(OperandValue::Immediate)
432                            .unwrap_or_else(|| {
433                                bug!("Unsupported cast of {operand:?} to {cast:?}");
434                            })
435                    }
436                    mir::CastKind::Transmute => {
437                        self.codegen_transmute_operand(bx, operand, cast)
438                    }
439                };
440                OperandRef { val, layout: cast }
441            }
442
443            mir::Rvalue::Ref(_, bk, place) => {
444                let mk_ref = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
445                    Ty::new_ref(tcx, tcx.lifetimes.re_erased, ty, bk.to_mutbl_lossy())
446                };
447                self.codegen_place_to_pointer(bx, place, mk_ref)
448            }
449
450            mir::Rvalue::CopyForDeref(place) => {
451                self.codegen_operand(bx, &mir::Operand::Copy(place))
452            }
453            mir::Rvalue::RawPtr(kind, place) => {
454                let mk_ptr = move |tcx: TyCtxt<'tcx>, ty: Ty<'tcx>| {
455                    Ty::new_ptr(tcx, ty, kind.to_mutbl_lossy())
456                };
457                self.codegen_place_to_pointer(bx, place, mk_ptr)
458            }
459
460            mir::Rvalue::Len(place) => {
461                let size = self.evaluate_array_len(bx, place);
462                OperandRef {
463                    val: OperandValue::Immediate(size),
464                    layout: bx.cx().layout_of(bx.tcx().types.usize),
465                }
466            }
467
468            mir::Rvalue::BinaryOp(op_with_overflow, box (ref lhs, ref rhs))
469                if let Some(op) = op_with_overflow.overflowing_to_wrapping() =>
470            {
471                let lhs = self.codegen_operand(bx, lhs);
472                let rhs = self.codegen_operand(bx, rhs);
473                let result = self.codegen_scalar_checked_binop(
474                    bx,
475                    op,
476                    lhs.immediate(),
477                    rhs.immediate(),
478                    lhs.layout.ty,
479                );
480                let val_ty = op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty);
481                let operand_ty = Ty::new_tup(bx.tcx(), &[val_ty, bx.tcx().types.bool]);
482                OperandRef { val: result, layout: bx.cx().layout_of(operand_ty) }
483            }
484            mir::Rvalue::BinaryOp(op, box (ref lhs, ref rhs)) => {
485                let lhs = self.codegen_operand(bx, lhs);
486                let rhs = self.codegen_operand(bx, rhs);
487                let llresult = match (lhs.val, rhs.val) {
488                    (
489                        OperandValue::Pair(lhs_addr, lhs_extra),
490                        OperandValue::Pair(rhs_addr, rhs_extra),
491                    ) => self.codegen_wide_ptr_binop(
492                        bx,
493                        op,
494                        lhs_addr,
495                        lhs_extra,
496                        rhs_addr,
497                        rhs_extra,
498                        lhs.layout.ty,
499                    ),
500
501                    (OperandValue::Immediate(lhs_val), OperandValue::Immediate(rhs_val)) => self
502                        .codegen_scalar_binop(
503                            bx,
504                            op,
505                            lhs_val,
506                            rhs_val,
507                            lhs.layout.ty,
508                            rhs.layout.ty,
509                        ),
510
511                    _ => bug!(),
512                };
513                OperandRef {
514                    val: OperandValue::Immediate(llresult),
515                    layout: bx.cx().layout_of(op.ty(bx.tcx(), lhs.layout.ty, rhs.layout.ty)),
516                }
517            }
518
519            mir::Rvalue::UnaryOp(op, ref operand) => {
520                let operand = self.codegen_operand(bx, operand);
521                let is_float = operand.layout.ty.is_floating_point();
522                let (val, layout) = match op {
523                    mir::UnOp::Not => {
524                        let llval = bx.not(operand.immediate());
525                        (OperandValue::Immediate(llval), operand.layout)
526                    }
527                    mir::UnOp::Neg => {
528                        let llval = if is_float {
529                            bx.fneg(operand.immediate())
530                        } else {
531                            bx.neg(operand.immediate())
532                        };
533                        (OperandValue::Immediate(llval), operand.layout)
534                    }
535                    mir::UnOp::PtrMetadata => {
536                        assert!(operand.layout.ty.is_raw_ptr() || operand.layout.ty.is_ref(),);
537                        let (_, meta) = operand.val.pointer_parts();
538                        assert_eq!(operand.layout.fields.count() > 1, meta.is_some());
539                        if let Some(meta) = meta {
540                            (OperandValue::Immediate(meta), operand.layout.field(self.cx, 1))
541                        } else {
542                            (OperandValue::ZeroSized, bx.cx().layout_of(bx.tcx().types.unit))
543                        }
544                    }
545                };
546                assert!(
547                    val.is_expected_variant_for_type(self.cx, layout),
548                    "Made wrong variant {val:?} for type {layout:?}",
549                );
550                OperandRef { val, layout }
551            }
552
553            mir::Rvalue::Discriminant(ref place) => {
554                let discr_ty = rvalue.ty(self.mir, bx.tcx());
555                let discr_ty = self.monomorphize(discr_ty);
556                let operand = self.codegen_consume(bx, place.as_ref());
557                let discr = operand.codegen_get_discr(self, bx, discr_ty);
558                OperandRef {
559                    val: OperandValue::Immediate(discr),
560                    layout: self.cx.layout_of(discr_ty),
561                }
562            }
563
564            mir::Rvalue::NullaryOp(ref null_op, ty) => {
565                let ty = self.monomorphize(ty);
566                let layout = bx.cx().layout_of(ty);
567                let val = match null_op {
568                    mir::NullOp::SizeOf => {
569                        assert!(bx.cx().type_is_sized(ty));
570                        let val = layout.size.bytes();
571                        bx.cx().const_usize(val)
572                    }
573                    mir::NullOp::AlignOf => {
574                        assert!(bx.cx().type_is_sized(ty));
575                        let val = layout.align.abi.bytes();
576                        bx.cx().const_usize(val)
577                    }
578                    mir::NullOp::OffsetOf(fields) => {
579                        let val = bx
580                            .tcx()
581                            .offset_of_subfield(bx.typing_env(), layout, fields.iter())
582                            .bytes();
583                        bx.cx().const_usize(val)
584                    }
585                    mir::NullOp::UbChecks => {
586                        let val = bx.tcx().sess.ub_checks();
587                        bx.cx().const_bool(val)
588                    }
589                    mir::NullOp::ContractChecks => {
590                        let val = bx.tcx().sess.contract_checks();
591                        bx.cx().const_bool(val)
592                    }
593                };
594                let tcx = self.cx.tcx();
595                OperandRef {
596                    val: OperandValue::Immediate(val),
597                    layout: self.cx.layout_of(null_op.ty(tcx)),
598                }
599            }
600
601            mir::Rvalue::ThreadLocalRef(def_id) => {
602                assert!(bx.cx().tcx().is_static(def_id));
603                let layout = bx.layout_of(bx.cx().tcx().static_ptr_ty(def_id, bx.typing_env()));
604                let static_ = if !def_id.is_local() && bx.cx().tcx().needs_thread_local_shim(def_id)
605                {
606                    let instance = ty::Instance {
607                        def: ty::InstanceKind::ThreadLocalShim(def_id),
608                        args: ty::GenericArgs::empty(),
609                    };
610                    let fn_ptr = bx.get_fn_addr(instance);
611                    let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
612                    let fn_ty = bx.fn_decl_backend_type(fn_abi);
613                    let fn_attrs = if bx.tcx().def_kind(instance.def_id()).has_codegen_attrs() {
614                        Some(bx.tcx().codegen_instance_attrs(instance.def))
615                    } else {
616                        None
617                    };
618                    bx.call(
619                        fn_ty,
620                        fn_attrs.as_deref(),
621                        Some(fn_abi),
622                        fn_ptr,
623                        &[],
624                        None,
625                        Some(instance),
626                    )
627                } else {
628                    bx.get_static(def_id)
629                };
630                OperandRef { val: OperandValue::Immediate(static_), layout }
631            }
632            mir::Rvalue::Use(ref operand) => self.codegen_operand(bx, operand),
633            mir::Rvalue::Repeat(..) => bug!("{rvalue:?} in codegen_rvalue_operand"),
634            mir::Rvalue::Aggregate(ref kind, ref fields) => {
635                let (variant_index, active_field_index) = match **kind {
636                    mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
637                        (variant_index, active_field_index)
638                    }
639                    _ => (FIRST_VARIANT, None),
640                };
641
642                let ty = rvalue.ty(self.mir, self.cx.tcx());
643                let ty = self.monomorphize(ty);
644                let layout = self.cx.layout_of(ty);
645
646                // `rvalue_creates_operand` has arranged that we only get here if
647                // we can build the aggregate immediate from the field immediates.
648                let mut builder = OperandRefBuilder::new(layout);
649                for (field_idx, field) in fields.iter_enumerated() {
650                    let op = self.codegen_operand(bx, field);
651                    let fi = active_field_index.unwrap_or(field_idx);
652                    builder.insert_field(bx, variant_index, fi, op);
653                }
654
655                let tag_result = codegen_tag_value(self.cx, variant_index, layout);
656                match tag_result {
657                    Err(super::place::UninhabitedVariantError) => {
658                        // Like codegen_set_discr we use a sound abort, but could
659                        // potentially `unreachable` or just return the poison for
660                        // more optimizability, if that turns out to be helpful.
661                        bx.abort();
662                        let val = OperandValue::poison(bx, layout);
663                        OperandRef { val, layout }
664                    }
665                    Ok(maybe_tag_value) => {
666                        if let Some((tag_field, tag_imm)) = maybe_tag_value {
667                            builder.insert_imm(tag_field, tag_imm);
668                        }
669                        builder.build(bx.cx())
670                    }
671                }
672            }
673            mir::Rvalue::ShallowInitBox(ref operand, content_ty) => {
674                let operand = self.codegen_operand(bx, operand);
675                let val = operand.immediate();
676
677                let content_ty = self.monomorphize(content_ty);
678                let box_layout = bx.cx().layout_of(Ty::new_box(bx.tcx(), content_ty));
679
680                OperandRef { val: OperandValue::Immediate(val), layout: box_layout }
681            }
682            mir::Rvalue::WrapUnsafeBinder(ref operand, binder_ty) => {
683                let operand = self.codegen_operand(bx, operand);
684                let binder_ty = self.monomorphize(binder_ty);
685                let layout = bx.cx().layout_of(binder_ty);
686                OperandRef { val: operand.val, layout }
687            }
688        }
689    }
690
691    fn evaluate_array_len(&mut self, bx: &mut Bx, place: mir::Place<'tcx>) -> Bx::Value {
692        // ZST are passed as operands and require special handling
693        // because codegen_place() panics if Local is operand.
694        if let Some(index) = place.as_local()
695            && let LocalRef::Operand(op) = self.locals[index]
696            && let ty::Array(_, n) = op.layout.ty.kind()
697        {
698            let n = n.try_to_target_usize(bx.tcx()).expect("expected monomorphic const in codegen");
699            return bx.cx().const_usize(n);
700        }
701        // use common size calculation for non zero-sized types
702        let cg_value = self.codegen_place(bx, place.as_ref());
703        cg_value.len(bx.cx())
704    }
705
706    /// Codegen an `Rvalue::RawPtr` or `Rvalue::Ref`
707    fn codegen_place_to_pointer(
708        &mut self,
709        bx: &mut Bx,
710        place: mir::Place<'tcx>,
711        mk_ptr_ty: impl FnOnce(TyCtxt<'tcx>, Ty<'tcx>) -> Ty<'tcx>,
712    ) -> OperandRef<'tcx, Bx::Value> {
713        let cg_place = self.codegen_place(bx, place.as_ref());
714        let val = cg_place.val.address();
715
716        let ty = cg_place.layout.ty;
717        assert!(
718            if bx.cx().tcx().type_has_metadata(ty, bx.cx().typing_env()) {
719                matches!(val, OperandValue::Pair(..))
720            } else {
721                matches!(val, OperandValue::Immediate(..))
722            },
723            "Address of place was unexpectedly {val:?} for pointee type {ty:?}",
724        );
725
726        OperandRef { val, layout: self.cx.layout_of(mk_ptr_ty(self.cx.tcx(), ty)) }
727    }
728
729    fn codegen_scalar_binop(
730        &mut self,
731        bx: &mut Bx,
732        op: mir::BinOp,
733        lhs: Bx::Value,
734        rhs: Bx::Value,
735        lhs_ty: Ty<'tcx>,
736        rhs_ty: Ty<'tcx>,
737    ) -> Bx::Value {
738        let is_float = lhs_ty.is_floating_point();
739        let is_signed = lhs_ty.is_signed();
740        match op {
741            mir::BinOp::Add => {
742                if is_float {
743                    bx.fadd(lhs, rhs)
744                } else {
745                    bx.add(lhs, rhs)
746                }
747            }
748            mir::BinOp::AddUnchecked => {
749                if is_signed {
750                    bx.unchecked_sadd(lhs, rhs)
751                } else {
752                    bx.unchecked_uadd(lhs, rhs)
753                }
754            }
755            mir::BinOp::Sub => {
756                if is_float {
757                    bx.fsub(lhs, rhs)
758                } else {
759                    bx.sub(lhs, rhs)
760                }
761            }
762            mir::BinOp::SubUnchecked => {
763                if is_signed {
764                    bx.unchecked_ssub(lhs, rhs)
765                } else {
766                    bx.unchecked_usub(lhs, rhs)
767                }
768            }
769            mir::BinOp::Mul => {
770                if is_float {
771                    bx.fmul(lhs, rhs)
772                } else {
773                    bx.mul(lhs, rhs)
774                }
775            }
776            mir::BinOp::MulUnchecked => {
777                if is_signed {
778                    bx.unchecked_smul(lhs, rhs)
779                } else {
780                    bx.unchecked_umul(lhs, rhs)
781                }
782            }
783            mir::BinOp::Div => {
784                if is_float {
785                    bx.fdiv(lhs, rhs)
786                } else if is_signed {
787                    bx.sdiv(lhs, rhs)
788                } else {
789                    bx.udiv(lhs, rhs)
790                }
791            }
792            mir::BinOp::Rem => {
793                if is_float {
794                    bx.frem(lhs, rhs)
795                } else if is_signed {
796                    bx.srem(lhs, rhs)
797                } else {
798                    bx.urem(lhs, rhs)
799                }
800            }
801            mir::BinOp::BitOr => bx.or(lhs, rhs),
802            mir::BinOp::BitAnd => bx.and(lhs, rhs),
803            mir::BinOp::BitXor => bx.xor(lhs, rhs),
804            mir::BinOp::Offset => {
805                let pointee_type = lhs_ty
806                    .builtin_deref(true)
807                    .unwrap_or_else(|| bug!("deref of non-pointer {:?}", lhs_ty));
808                let pointee_layout = bx.cx().layout_of(pointee_type);
809                if pointee_layout.is_zst() {
810                    // `Offset` works in terms of the size of pointee,
811                    // so offsetting a pointer to ZST is a noop.
812                    lhs
813                } else {
814                    let llty = bx.cx().backend_type(pointee_layout);
815                    if !rhs_ty.is_signed() {
816                        bx.inbounds_nuw_gep(llty, lhs, &[rhs])
817                    } else {
818                        bx.inbounds_gep(llty, lhs, &[rhs])
819                    }
820                }
821            }
822            mir::BinOp::Shl | mir::BinOp::ShlUnchecked => {
823                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShlUnchecked);
824                bx.shl(lhs, rhs)
825            }
826            mir::BinOp::Shr | mir::BinOp::ShrUnchecked => {
827                let rhs = base::build_shift_expr_rhs(bx, lhs, rhs, op == mir::BinOp::ShrUnchecked);
828                if is_signed { bx.ashr(lhs, rhs) } else { bx.lshr(lhs, rhs) }
829            }
830            mir::BinOp::Ne
831            | mir::BinOp::Lt
832            | mir::BinOp::Gt
833            | mir::BinOp::Eq
834            | mir::BinOp::Le
835            | mir::BinOp::Ge => {
836                if is_float {
837                    bx.fcmp(base::bin_op_to_fcmp_predicate(op), lhs, rhs)
838                } else {
839                    bx.icmp(base::bin_op_to_icmp_predicate(op, is_signed), lhs, rhs)
840                }
841            }
842            mir::BinOp::Cmp => {
843                use std::cmp::Ordering;
844                assert!(!is_float);
845                if let Some(value) = bx.three_way_compare(lhs_ty, lhs, rhs) {
846                    return value;
847                }
848                let pred = |op| base::bin_op_to_icmp_predicate(op, is_signed);
849                if bx.cx().tcx().sess.opts.optimize == OptLevel::No {
850                    // FIXME: This actually generates tighter assembly, and is a classic trick
851                    // <https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>
852                    // However, as of 2023-11 it optimizes worse in things like derived
853                    // `PartialOrd`, so only use it in debug for now. Once LLVM can handle it
854                    // better (see <https://github.com/llvm/llvm-project/issues/73417>), it'll
855                    // be worth trying it in optimized builds as well.
856                    let is_gt = bx.icmp(pred(mir::BinOp::Gt), lhs, rhs);
857                    let gtext = bx.zext(is_gt, bx.type_i8());
858                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
859                    let ltext = bx.zext(is_lt, bx.type_i8());
860                    bx.unchecked_ssub(gtext, ltext)
861                } else {
862                    // These operations are those expected by `tests/codegen/integer-cmp.rs`,
863                    // from <https://github.com/rust-lang/rust/pull/63767>.
864                    let is_lt = bx.icmp(pred(mir::BinOp::Lt), lhs, rhs);
865                    let is_ne = bx.icmp(pred(mir::BinOp::Ne), lhs, rhs);
866                    let ge = bx.select(
867                        is_ne,
868                        bx.cx().const_i8(Ordering::Greater as i8),
869                        bx.cx().const_i8(Ordering::Equal as i8),
870                    );
871                    bx.select(is_lt, bx.cx().const_i8(Ordering::Less as i8), ge)
872                }
873            }
874            mir::BinOp::AddWithOverflow
875            | mir::BinOp::SubWithOverflow
876            | mir::BinOp::MulWithOverflow => {
877                bug!("{op:?} needs to return a pair, so call codegen_scalar_checked_binop instead")
878            }
879        }
880    }
881
882    fn codegen_wide_ptr_binop(
883        &mut self,
884        bx: &mut Bx,
885        op: mir::BinOp,
886        lhs_addr: Bx::Value,
887        lhs_extra: Bx::Value,
888        rhs_addr: Bx::Value,
889        rhs_extra: Bx::Value,
890        _input_ty: Ty<'tcx>,
891    ) -> Bx::Value {
892        match op {
893            mir::BinOp::Eq => {
894                let lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
895                let rhs = bx.icmp(IntPredicate::IntEQ, lhs_extra, rhs_extra);
896                bx.and(lhs, rhs)
897            }
898            mir::BinOp::Ne => {
899                let lhs = bx.icmp(IntPredicate::IntNE, lhs_addr, rhs_addr);
900                let rhs = bx.icmp(IntPredicate::IntNE, lhs_extra, rhs_extra);
901                bx.or(lhs, rhs)
902            }
903            mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
904                // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
905                let (op, strict_op) = match op {
906                    mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
907                    mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
908                    mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
909                    mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
910                    _ => bug!(),
911                };
912                let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
913                let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
914                let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
915                let rhs = bx.and(and_lhs, and_rhs);
916                bx.or(lhs, rhs)
917            }
918            _ => {
919                bug!("unexpected wide ptr binop");
920            }
921        }
922    }
923
924    fn codegen_scalar_checked_binop(
925        &mut self,
926        bx: &mut Bx,
927        op: mir::BinOp,
928        lhs: Bx::Value,
929        rhs: Bx::Value,
930        input_ty: Ty<'tcx>,
931    ) -> OperandValue<Bx::Value> {
932        let (val, of) = match op {
933            // These are checked using intrinsics
934            mir::BinOp::Add | mir::BinOp::Sub | mir::BinOp::Mul => {
935                let oop = match op {
936                    mir::BinOp::Add => OverflowOp::Add,
937                    mir::BinOp::Sub => OverflowOp::Sub,
938                    mir::BinOp::Mul => OverflowOp::Mul,
939                    _ => unreachable!(),
940                };
941                bx.checked_binop(oop, input_ty, lhs, rhs)
942            }
943            _ => bug!("Operator `{:?}` is not a checkable operator", op),
944        };
945
946        OperandValue::Pair(val, of)
947    }
948
949    /// Returns `true` if the `rvalue` can be computed into an [`OperandRef`],
950    /// rather than needing a full `PlaceRef` for the assignment destination.
951    ///
952    /// This is used by the [`super::analyze`] code to decide which MIR locals
953    /// can stay as SSA values (as opposed to generating `alloca` slots for them).
954    /// As such, some paths here return `true` even where the specific rvalue
955    /// will not actually take the operand path because the result type is such
956    /// that it always gets an `alloca`, but where it's not worth re-checking the
957    /// layout in this code when the right thing will happen anyway.
958    pub(crate) fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>) -> bool {
959        match *rvalue {
960            mir::Rvalue::Cast(mir::CastKind::Transmute, ref operand, cast_ty) => {
961                let operand_ty = operand.ty(self.mir, self.cx.tcx());
962                let cast_layout = self.cx.layout_of(self.monomorphize(cast_ty));
963                let operand_layout = self.cx.layout_of(self.monomorphize(operand_ty));
964                match (operand_layout.backend_repr, cast_layout.backend_repr) {
965                    // When the output will be in memory anyway, just use its place
966                    // (instead of the operand path) unless it's the trivial ZST case.
967                    (_, abi::BackendRepr::Memory { .. }) => cast_layout.is_zst(),
968
969                    // Otherwise (for a non-memory output) if the input is memory
970                    // then we can just read the value from the place.
971                    (abi::BackendRepr::Memory { .. }, _) => true,
972
973                    // When we have scalar immediates, we can only convert things
974                    // where the sizes match, to avoid endianness questions.
975                    (abi::BackendRepr::Scalar(a), abi::BackendRepr::Scalar(b)) =>
976                        a.size(self.cx) == b.size(self.cx),
977                    (abi::BackendRepr::ScalarPair(a0, a1), abi::BackendRepr::ScalarPair(b0, b1)) =>
978                        a0.size(self.cx) == b0.size(self.cx) && a1.size(self.cx) == b1.size(self.cx),
979
980                    // Mixing Scalars and ScalarPairs can get quite complicated when
981                    // padding and undef get involved, so leave that to the memory path.
982                    (abi::BackendRepr::Scalar(_), abi::BackendRepr::ScalarPair(_, _)) |
983                    (abi::BackendRepr::ScalarPair(_, _), abi::BackendRepr::Scalar(_)) => false,
984
985                    // SIMD vectors aren't worth the trouble of dealing with complex
986                    // cases like from vectors of f32 to vectors of pointers or
987                    // from fat pointers to vectors of u16. (See #143194 #110021 ...)
988                    (abi::BackendRepr::SimdVector { .. }, _) | (_, abi::BackendRepr::SimdVector { .. }) => false,
989                }
990            }
991            mir::Rvalue::Ref(..) |
992            mir::Rvalue::CopyForDeref(..) |
993            mir::Rvalue::RawPtr(..) |
994            mir::Rvalue::Len(..) |
995            mir::Rvalue::Cast(..) | // (*)
996            mir::Rvalue::ShallowInitBox(..) | // (*)
997            mir::Rvalue::BinaryOp(..) |
998            mir::Rvalue::UnaryOp(..) |
999            mir::Rvalue::Discriminant(..) |
1000            mir::Rvalue::NullaryOp(..) |
1001            mir::Rvalue::ThreadLocalRef(_) |
1002            mir::Rvalue::Use(..) |
1003            mir::Rvalue::Aggregate(..) | // (*)
1004            mir::Rvalue::WrapUnsafeBinder(..) => // (*)
1005                true,
1006            // Arrays are always aggregates, so it's not worth checking anything here.
1007            // (If it's really `[(); N]` or `[T; 0]` and we use the place path, fine.)
1008            mir::Rvalue::Repeat(..) => false,
1009        }
1010
1011        // (*) this is only true if the type is suitable
1012    }
1013}
1014
1015/// Transmutes a single scalar value `imm` from `from_scalar` to `to_scalar`.
1016///
1017/// This is expected to be in *immediate* form, as seen in [`OperandValue::Immediate`]
1018/// or [`OperandValue::Pair`] (so `i1` for bools, not `i8`, for example).
1019///
1020/// ICEs if the passed-in `imm` is not a value of the expected type for
1021/// `from_scalar`, such as if it's a vector or a pair.
1022pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
1023    bx: &mut Bx,
1024    mut imm: Bx::Value,
1025    from_scalar: abi::Scalar,
1026    to_scalar: abi::Scalar,
1027) -> Bx::Value {
1028    assert_eq!(from_scalar.size(bx.cx()), to_scalar.size(bx.cx()));
1029    let imm_ty = bx.cx().val_ty(imm);
1030    assert_ne!(
1031        bx.cx().type_kind(imm_ty),
1032        TypeKind::Vector,
1033        "Vector type {imm_ty:?} not allowed in transmute_scalar {from_scalar:?} -> {to_scalar:?}"
1034    );
1035
1036    // While optimizations will remove no-op transmutes, they might still be
1037    // there in debug or things that aren't no-op in MIR because they change
1038    // the Rust type but not the underlying layout/niche.
1039    if from_scalar == to_scalar {
1040        return imm;
1041    }
1042
1043    use abi::Primitive::*;
1044    imm = bx.from_immediate(imm);
1045
1046    let from_backend_ty = bx.cx().type_from_scalar(from_scalar);
1047    debug_assert_eq!(bx.cx().val_ty(imm), from_backend_ty);
1048    let to_backend_ty = bx.cx().type_from_scalar(to_scalar);
1049
1050    // If we have a scalar, we must already know its range. Either
1051    //
1052    // 1) It's a parameter with `range` parameter metadata,
1053    // 2) It's something we `load`ed with `!range` metadata, or
1054    // 3) After a transmute we `assume`d the range (see below).
1055    //
1056    // That said, last time we tried removing this, it didn't actually help
1057    // the rustc-perf results, so might as well keep doing it
1058    // <https://github.com/rust-lang/rust/pull/135610#issuecomment-2599275182>
1059    assume_scalar_range(bx, imm, from_scalar, from_backend_ty);
1060
1061    imm = match (from_scalar.primitive(), to_scalar.primitive()) {
1062        (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
1063        (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
1064        (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
1065        (Pointer(..), Int(..)) => {
1066            // FIXME: this exposes the provenance, which shouldn't be necessary.
1067            bx.ptrtoint(imm, to_backend_ty)
1068        }
1069        (Float(_), Pointer(..)) => {
1070            let int_imm = bx.bitcast(imm, bx.cx().type_isize());
1071            bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
1072        }
1073        (Pointer(..), Float(_)) => {
1074            // FIXME: this exposes the provenance, which shouldn't be necessary.
1075            let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
1076            bx.bitcast(int_imm, to_backend_ty)
1077        }
1078    };
1079
1080    debug_assert_eq!(bx.cx().val_ty(imm), to_backend_ty);
1081
1082    // This `assume` remains important for cases like (a conceptual)
1083    //    transmute::<u32, NonZeroU32>(x) == 0
1084    // since it's never passed to something with parameter metadata (especially
1085    // after MIR inlining) so the only way to tell the backend about the
1086    // constraint that the `transmute` introduced is to `assume` it.
1087    assume_scalar_range(bx, imm, to_scalar, to_backend_ty);
1088
1089    imm = bx.to_immediate_scalar(imm, to_scalar);
1090    imm
1091}
1092
1093fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
1094    bx: &mut Bx,
1095    imm: Bx::Value,
1096    scalar: abi::Scalar,
1097    backend_ty: Bx::Type,
1098) {
1099    if matches!(bx.cx().sess().opts.optimize, OptLevel::No) || scalar.is_always_valid(bx.cx()) {
1100        return;
1101    }
1102
1103    match scalar.primitive() {
1104        abi::Primitive::Int(..) => {
1105            let range = scalar.valid_range(bx.cx());
1106            bx.assume_integer_range(imm, backend_ty, range);
1107        }
1108        abi::Primitive::Pointer(abi::AddressSpace::ZERO)
1109            if !scalar.valid_range(bx.cx()).contains(0) =>
1110        {
1111            bx.assume_nonnull(imm);
1112        }
1113        abi::Primitive::Pointer(..) | abi::Primitive::Float(..) => {}
1114    }
1115}
rustc_codegen_ssa/mir/rvalue.rs

rustc_codegen_ssa/mir/
rvalue.rs
