diff options
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/operand.rs | 6 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/dataflow_const_prop.rs | 7 | ||||
| -rw-r--r-- | tests/mir-opt/gvn_uninhabited.f.GVN.panic-abort.diff | 34 | ||||
| -rw-r--r-- | tests/mir-opt/gvn_uninhabited.f.GVN.panic-unwind.diff | 34 | ||||
| -rw-r--r-- | tests/mir-opt/gvn_uninhabited.rs | 24 |
5 files changed, 98 insertions, 7 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs index 80d4bda4827..4653c9016c6 100644 --- a/compiler/rustc_const_eval/src/interpret/operand.rs +++ b/compiler/rustc_const_eval/src/interpret/operand.rs @@ -260,8 +260,12 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> { // This makes several assumptions about what layouts we will encounter; we match what // codegen does as good as we can (see `extract_field` in `rustc_codegen_ssa/src/mir/operand.rs`). let inner_val: Immediate<_> = match (**self, self.layout.abi) { - // if the entire value is uninit, then so is the field (can happen in ConstProp) + // If the entire value is uninit, then so is the field (can happen in ConstProp). (Immediate::Uninit, _) => Immediate::Uninit, + // If the field is uninhabited, we can forget the data (can happen in ConstProp). + // `enum S { A(!), B, C }` is an example of an enum with Scalar layout that + // has an `Uninhabited` variant, which means this case is possible. + _ if layout.abi.is_uninhabited() => Immediate::Uninit, // the field contains no information, can be left uninit // (Scalar/ScalarPair can contain even aligned ZST, not just 1-ZST) _ if layout.is_zst() => Immediate::Uninit, diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index d5f22b2cdbc..ad12bce9b02 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -403,12 +403,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> { operand, &mut |elem, op| match elem { TrackElem::Field(idx) => self.ecx.project_field(op, idx.as_usize()).ok(), - TrackElem::Variant(idx) => { - if op.layout.for_variant(&self.ecx, idx).abi.is_uninhabited() { - return None; - } - self.ecx.project_downcast(op, idx).ok() - } + TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).ok(), TrackElem::Discriminant => { let variant = self.ecx.read_discriminant(op).ok()?; let discr_value = diff --git a/tests/mir-opt/gvn_uninhabited.f.GVN.panic-abort.diff b/tests/mir-opt/gvn_uninhabited.f.GVN.panic-abort.diff new file mode 100644 index 00000000000..0b6819ad483 --- /dev/null +++ b/tests/mir-opt/gvn_uninhabited.f.GVN.panic-abort.diff @@ -0,0 +1,34 @@ +- // MIR for `f` before GVN ++ // MIR for `f` after GVN + + fn f() -> u32 { + let mut _0: u32; + let _1: u32; + let mut _2: E; + let mut _3: &U; + let _4: U; + scope 1 { + debug i => _1; + } + scope 2 { + let mut _5: &U; + } + + bb0: { + StorageLive(_2); + StorageLive(_3); + _5 = const _; + _3 = &(*_5); + _2 = ((*_3).1: E); + StorageLive(_1); +- _1 = ((_2 as A).1: u32); ++ _1 = const 0_u32; + StorageDead(_3); + StorageDead(_2); +- _0 = _1; ++ _0 = const 0_u32; + StorageDead(_1); + return; + } + } + diff --git a/tests/mir-opt/gvn_uninhabited.f.GVN.panic-unwind.diff b/tests/mir-opt/gvn_uninhabited.f.GVN.panic-unwind.diff new file mode 100644 index 00000000000..0b6819ad483 --- /dev/null +++ b/tests/mir-opt/gvn_uninhabited.f.GVN.panic-unwind.diff @@ -0,0 +1,34 @@ +- // MIR for `f` before GVN ++ // MIR for `f` after GVN + + fn f() -> u32 { + let mut _0: u32; + let _1: u32; + let mut _2: E; + let mut _3: &U; + let _4: U; + scope 1 { + debug i => _1; + } + scope 2 { + let mut _5: &U; + } + + bb0: { + StorageLive(_2); + StorageLive(_3); + _5 = const _; + _3 = &(*_5); + _2 = ((*_3).1: E); + StorageLive(_1); +- _1 = ((_2 as A).1: u32); ++ _1 = const 0_u32; + StorageDead(_3); + StorageDead(_2); +- _0 = _1; ++ _0 = const 0_u32; + StorageDead(_1); + return; + } + } + diff --git a/tests/mir-opt/gvn_uninhabited.rs b/tests/mir-opt/gvn_uninhabited.rs new file mode 100644 index 00000000000..a55b2dd763a --- /dev/null +++ b/tests/mir-opt/gvn_uninhabited.rs @@ -0,0 +1,24 @@ +// unit-test: GVN +// compile-flags: -O +// EMIT_MIR_FOR_EACH_PANIC_STRATEGY +// skip-filecheck + +#![feature(never_type)] + +#[derive(Copy, Clone)] +pub enum E { + A(!, u32), +} + +pub union U { + i: u32, + e: E, +} + +// EMIT_MIR gvn_uninhabited.f.GVN.diff +pub const fn f() -> u32 { + let E::A(_, i) = unsafe { (&U { i: 0 }).e }; + i +} + +fn main() {} |