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Rollup merge of #89764 - tmiasko:uninhabited-enums, r=wesleywiser

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Fix variant index / discriminant confusion in uninhabited enum branching

Fix confusion between variant index and variant discriminant. The pass
incorrectly assumed that for `Variants::Single` variant index is the same as
variant discriminant.

r? `@wesleywiser`
This commit is contained in:
Matthias Krüger 2022-01-20 17:10:31 +01:00 • committed by GitHub
commit d188287a54
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1 changed files with 6 additions and 11 deletions
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17
compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
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@ -3,8 +3,7 @@
use crate::MirPass;
use rustc_data_structures::stable_set::FxHashSet;
use rustc_middle::mir::{
BasicBlock, BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, SwitchTargets,
TerminatorKind,
BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, SwitchTargets, TerminatorKind,
};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{Ty, TyCtxt};
@ -56,7 +55,10 @@ fn variant_discriminants<'tcx>(
match &layout.variants {
Variants::Single { index } => {
let mut res = FxHashSet::default();
res.insert(index.as_u32() as u128);
res.insert(
ty.discriminant_for_variant(tcx, *index)
.map_or(index.as_u32() as u128, |discr| discr.val),
);
res
}
Variants::Multiple { variants, .. } => variants
@ -75,16 +77,9 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
if body.source.promoted.is_some() {
return;
}
trace!("UninhabitedEnumBranching starting for {:?}", body.source);
let basic_block_count = body.basic_blocks().len();
for bb in 0..basic_block_count {
let bb = BasicBlock::from_usize(bb);
for bb in body.basic_blocks().indices() {
trace!("processing block {:?}", bb);
let Some(discriminant_ty) = get_switched_on_type(&body.basic_blocks()[bb], tcx, body) else {