diff options
Diffstat (limited to 'compiler/rustc_codegen_ssa')
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/mir/operand.rs | 7 | ||||
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/mir/rvalue.rs | 86 |
2 files changed, 52 insertions, 41 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs index 4b1c689a010..568c54c6570 100644 --- a/compiler/rustc_codegen_ssa/src/mir/operand.rs +++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs @@ -355,12 +355,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> { self.val } else if field.size == self.layout.size { assert_eq!(offset.bytes(), 0); - fx.codegen_transmute_operand(bx, *self, field).unwrap_or_else(|| { - bug!( - "Expected `codegen_transmute_operand` to handle equal-size \ - field {i:?} projection from {self:?} to {field:?}" - ) - }) + fx.codegen_transmute_operand(bx, *self, field) } else { let (in_scalar, imm) = match (self.val, self.layout.backend_repr) { // Extract a scalar component from a pair. diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs index 589405e885f..f7e8d5dcab2 100644 --- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs +++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs @@ -188,6 +188,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { } } + /// Transmutes the `src` value to the destination type by writing it to `dst`. + /// + /// See also [`Self::codegen_transmute_operand`] for cases that can be done + /// without needing a pre-allocated place for the destination. fn codegen_transmute( &mut self, bx: &mut Bx, @@ -198,31 +202,36 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { assert!(src.layout.is_sized()); assert!(dst.layout.is_sized()); - if src.layout.size == dst.layout.size { + if src.layout.size != dst.layout.size + || src.layout.is_uninhabited() + || dst.layout.is_uninhabited() + { + // These cases are all UB to actually hit, so don't emit code for them. + // (The size mismatches are reachable via `transmute_unchecked`.) + // We can't use unreachable because that's a terminator, and we + // need something that can be in the middle of a basic block. + bx.assume(bx.cx().const_bool(false)) + } else { // Since in this path we have a place anyway, we can store or copy to it, // making sure we use the destination place's alignment even if the // source would normally have a higher one. src.val.store(bx, dst.val.with_type(src.layout)); - } else if src.layout.is_uninhabited() { - bx.unreachable() - } else { - // Since this is known statically and the input could have existed - // without already having hit UB, might as well trap for it, even - // though it's UB so we *could* also unreachable it. - bx.abort(); } } - /// Attempts to transmute an `OperandValue` to another `OperandValue`. + /// Transmutes an `OperandValue` to another `OperandValue`. /// - /// Returns `None` for cases that can't work in that framework, such as for - /// `Immediate`->`Ref` that needs an `alloca` to get the location. + /// This is supported only for cases where [`Self::rvalue_creates_operand`] + /// returns `true`, and will ICE otherwise. (In particular, anything that + /// would need to `alloca` in order to return a `PlaceValue` will ICE, + /// expecting those to go via [`Self::codegen_transmute`] instead where + /// the destination place is already allocated.) pub(crate) fn codegen_transmute_operand( &mut self, bx: &mut Bx, operand: OperandRef<'tcx, Bx::Value>, cast: TyAndLayout<'tcx>, - ) -> Option<OperandValue<Bx::Value>> { + ) -> OperandValue<Bx::Value> { // Check for transmutes that are always UB. if operand.layout.size != cast.size || operand.layout.is_uninhabited() @@ -236,17 +245,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { // Because this transmute is UB, return something easy to generate, // since it's fine that later uses of the value are probably UB. - return Some(OperandValue::poison(bx, cast)); + return OperandValue::poison(bx, cast); } - Some(match (operand.val, operand.layout.backend_repr, cast.backend_repr) { + match (operand.val, operand.layout.backend_repr, cast.backend_repr) { _ if cast.is_zst() => OperandValue::ZeroSized, - (OperandValue::ZeroSized, _, _) => bug!(), - ( - OperandValue::Ref(source_place_val), - abi::BackendRepr::Memory { .. }, - abi::BackendRepr::Scalar(_) | abi::BackendRepr::ScalarPair(_, _), - ) => { + (_, _, abi::BackendRepr::Memory { .. }) => { + bug!("Cannot `codegen_transmute_operand` to non-ZST memory-ABI output {cast:?}"); + } + (OperandValue::Ref(source_place_val), abi::BackendRepr::Memory { .. }, _) => { assert_eq!(source_place_val.llextra, None); // The existing alignment is part of `source_place_val`, // so that alignment will be used, not `cast`'s. @@ -265,8 +272,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { transmute_scalar(bx, imm_a, in_a, out_a), transmute_scalar(bx, imm_b, in_b, out_b), ), - _ => return None, - }) + _ => bug!("Cannot `codegen_transmute_operand` {operand:?} to {cast:?}"), + } } /// Cast one of the immediates from an [`OperandValue::Immediate`] @@ -458,9 +465,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { }) } mir::CastKind::Transmute => { - self.codegen_transmute_operand(bx, operand, cast).unwrap_or_else(|| { - bug!("Unsupported transmute-as-operand of {operand:?} to {cast:?}"); - }) + self.codegen_transmute_operand(bx, operand, cast) } }; OperandRef { val, layout: cast } @@ -942,6 +947,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { OperandValue::Pair(val, of) } + /// Returns `true` if the `rvalue` can be computed into an [`OperandRef`], + /// rather than needing a full `PlaceRef` for the assignment destination. + /// + /// This is used by the [`super::analyze`] code to decide which MIR locals + /// can stay as SSA values (as opposed to generating `alloca` slots for them). + /// As such, some paths here return `true` even where the specific rvalue + /// will not actually take the operand path because the result type is such + /// that it always gets an `alloca`, but where it's not worth re-checking the + /// layout in this code when the right thing will happen anyway. pub(crate) fn rvalue_creates_operand(&self, rvalue: &mir::Rvalue<'tcx>, span: Span) -> bool { match *rvalue { mir::Rvalue::Cast(mir::CastKind::Transmute, ref operand, cast_ty) => { @@ -949,8 +963,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { let cast_layout = self.cx.layout_of(self.monomorphize(cast_ty)); let operand_layout = self.cx.layout_of(self.monomorphize(operand_ty)); match (operand_layout.backend_repr, cast_layout.backend_repr) { - // If the input is in a place we can load immediates from there. - (abi::BackendRepr::Memory { .. }, abi::BackendRepr::Scalar(_) | abi::BackendRepr::ScalarPair(_, _)) => true, + // When the output will be in memory anyway, just use its place + // (instead of the operand path) unless it's the trivial ZST case. + (_, abi::BackendRepr::Memory { .. }) => cast_layout.is_zst(), + + // Otherwise (for a non-memory output) if the input is memory + // then we can just read the value from the place. + (abi::BackendRepr::Memory { .. }, _) => true, // When we have scalar immediates, we can only convert things // where the sizes match, to avoid endianness questions. @@ -959,18 +978,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { (abi::BackendRepr::ScalarPair(a0, a1), abi::BackendRepr::ScalarPair(b0, b1)) => a0.size(self.cx) == b0.size(self.cx) && a1.size(self.cx) == b1.size(self.cx), - // SIMD vectors don't work like normal immediates, - // so always send them through memory. - (abi::BackendRepr::SimdVector { .. }, _) | (_, abi::BackendRepr::SimdVector { .. }) => false, - - // When the output will be in memory anyway, just use its place - // (instead of the operand path) unless it's the trivial ZST case. - (_, abi::BackendRepr::Memory { .. }) => cast_layout.is_zst(), - // Mixing Scalars and ScalarPairs can get quite complicated when // padding and undef get involved, so leave that to the memory path. (abi::BackendRepr::Scalar(_), abi::BackendRepr::ScalarPair(_, _)) | (abi::BackendRepr::ScalarPair(_, _), abi::BackendRepr::Scalar(_)) => false, + + // SIMD vectors aren't worth the trouble of dealing with complex + // cases like from vectors of f32 to vectors of pointers or + // from fat pointers to vectors of u16. (See #143194 #110021 ...) + (abi::BackendRepr::SimdVector { .. }, _) | (_, abi::BackendRepr::SimdVector { .. }) => false, } } mir::Rvalue::Ref(..) | |