bjoernager/rust
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Replace the default branch with an unreachable branch If it is the last variant

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This commit is contained in:
DianQK 2024-02-14 12:02:22 +08:00
parent d8b7b5be7d
commit 08ae8380ce
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GPG key ID: 46BDB1AC96C48912
23 changed files with 997 additions and 11 deletions
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24
compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
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@ -78,6 +78,7 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
trace!("UninhabitedEnumBranching starting for {:?}", body.source);
let mut removable_switchs = Vec::new();
let mut otherwise_is_last_variant_switchs = Vec::new();
for (bb, bb_data) in body.basic_blocks.iter_enumerated() {
trace!("processing block {:?}", bb);
@ -92,7 +93,7 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
tcx.param_env_reveal_all_normalized(body.source.def_id()).and(discriminant_ty),
);
let allowed_variants = if let Ok(layout) = layout {
let mut allowed_variants = if let Ok(layout) = layout {
variant_discriminants(&layout, discriminant_ty, tcx)
} else {
continue;
@ -103,20 +104,31 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
let terminator = bb_data.terminator();
let TerminatorKind::SwitchInt { targets, .. } = &terminator.kind else { bug!() };
let mut reachable_count = 0;
for (index, (val, _)) in targets.iter().enumerate() {
if allowed_variants.contains(&val) {
reachable_count += 1;
} else {
if !allowed_variants.remove(&val) {
removable_switchs.push((bb, index));
}
}
if reachable_count == allowed_variants.len() {
if allowed_variants.is_empty() {
removable_switchs.push((bb, targets.iter().count()));
} else if allowed_variants.len() == 1
&& !body.basic_blocks[targets.otherwise()].is_empty_unreachable()
{
#[allow(rustc::potential_query_instability)]
let last_variant = *allowed_variants.iter().next().unwrap();
otherwise_is_last_variant_switchs.push((bb, last_variant));
}
}
for (bb, last_variant) in otherwise_is_last_variant_switchs {
let bb_data = &mut body.basic_blocks.as_mut()[bb];
let terminator = bb_data.terminator_mut();
let TerminatorKind::SwitchInt { targets, .. } = &mut terminator.kind else { bug!() };
targets.add_target(last_variant, targets.otherwise());
removable_switchs.push((bb, targets.iter().count()));
}
if removable_switchs.is_empty() {
return;
}