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Revert "Auto merge of rust-lang#120268 - DianQK:otherwise_is_last_var…
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…iant_switchs, r=oli-obk"

This reverts commit 14fbc3c, reversing
changes made to 9fb91aa.
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@DianQK
DianQK committed Mar 13, 2024
1 parent a165f1f commit 272dd0b
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Showing 38 changed files with 155 additions and 1,396 deletions.
27 changes: 2 additions & 25 deletions compiler/rustc_middle/src/mir/patch.rs
View file
Expand Up @@ -11,8 +11,6 @@ pub struct MirPatch<'tcx> {
resume_block: Option<BasicBlock>,
// Only for unreachable in cleanup path.
unreachable_cleanup_block: Option<BasicBlock>,
// Only for unreachable not in cleanup path.
unreachable_no_cleanup_block: Option<BasicBlock>,
// Cached block for UnwindTerminate (with reason)
terminate_block: Option<(BasicBlock, UnwindTerminateReason)>,
body_span: Span,
Expand All @@ -29,7 +27,6 @@ impl<'tcx> MirPatch<'tcx> {
next_local: body.local_decls.len(),
resume_block: None,
unreachable_cleanup_block: None,
unreachable_no_cleanup_block: None,
terminate_block: None,
body_span: body.span,
};
Expand All @@ -46,12 +43,9 @@ impl<'tcx> MirPatch<'tcx> {
// Check if we already have an unreachable block
if matches!(block.terminator().kind, TerminatorKind::Unreachable)
&& block.statements.is_empty()
&& block.is_cleanup
{
if block.is_cleanup {
result.unreachable_cleanup_block = Some(bb);
} else {
result.unreachable_no_cleanup_block = Some(bb);
}
result.unreachable_cleanup_block = Some(bb);
continue;
}

Expand Down Expand Up @@ -101,23 +95,6 @@ impl<'tcx> MirPatch<'tcx> {
bb
}

pub fn unreachable_no_cleanup_block(&mut self) -> BasicBlock {
if let Some(bb) = self.unreachable_no_cleanup_block {
return bb;
}

let bb = self.new_block(BasicBlockData {
statements: vec![],
terminator: Some(Terminator {
source_info: SourceInfo::outermost(self.body_span),
kind: TerminatorKind::Unreachable,
}),
is_cleanup: false,
});
self.unreachable_no_cleanup_block = Some(bb);
bb
}

pub fn terminate_block(&mut self, reason: UnwindTerminateReason) -> BasicBlock {
if let Some((cached_bb, cached_reason)) = self.terminate_block
&& reason == cached_reason
Expand Down
11 changes: 0 additions & 11 deletions compiler/rustc_middle/src/mir/terminator.rs
View file
Expand Up @@ -74,17 +74,6 @@ impl SwitchTargets {
pub fn target_for_value(&self, value: u128) -> BasicBlock {
self.iter().find_map(|(v, t)| (v == value).then_some(t)).unwrap_or_else(|| self.otherwise())
}

/// Adds a new target to the switch. But You cannot add an already present value.
#[inline]
pub fn add_target(&mut self, value: u128, bb: BasicBlock) {
let value = Pu128(value);
if self.values.contains(&value) {
bug!("target value {:?} already present", value);
}
self.values.push(value);
self.targets.insert(self.targets.len() - 1, bb);
}
}

pub struct SwitchTargetsIter<'a> {
Expand Down
84 changes: 27 additions & 57 deletions compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
View file
Expand Up @@ -2,10 +2,8 @@

use crate::MirPass;
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::mir::patch::MirPatch;
use rustc_middle::mir::{
BasicBlock, BasicBlockData, BasicBlocks, Body, Local, Operand, Rvalue, StatementKind,
TerminatorKind,
BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, Terminator, TerminatorKind,
};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{Ty, TyCtxt};
Expand Down Expand Up @@ -79,8 +77,7 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
trace!("UninhabitedEnumBranching starting for {:?}", body.source);

let mut unreachable_targets = Vec::new();
let mut patch = MirPatch::new(body);
let mut removable_switchs = Vec::new();

for (bb, bb_data) in body.basic_blocks.iter_enumerated() {
trace!("processing block {:?}", bb);
Expand All @@ -95,73 +92,46 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
tcx.param_env_reveal_all_normalized(body.source.def_id()).and(discriminant_ty),
);

let mut allowed_variants = if let Ok(layout) = layout {
let allowed_variants = if let Ok(layout) = layout {
variant_discriminants(&layout, discriminant_ty, tcx)
} else if let Some(variant_range) = discriminant_ty.variant_range(tcx) {
variant_range
.map(|variant| {
discriminant_ty.discriminant_for_variant(tcx, variant).unwrap().val
})
.collect()
} else {
continue;
};

trace!("allowed_variants = {:?}", allowed_variants);

unreachable_targets.clear();
let TerminatorKind::SwitchInt { targets, discr } = &bb_data.terminator().kind else {
bug!()
};
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.remove(&val) {
unreachable_targets.push(index);
}
}
let otherwise_is_empty_unreachable =
body.basic_blocks[targets.otherwise()].is_empty_unreachable();
// After resolving https://github.com/llvm/llvm-project/issues/78578,
// we can remove the limit on the number of successors.
fn check_successors(basic_blocks: &BasicBlocks<'_>, bb: BasicBlock) -> bool {
let mut successors = basic_blocks[bb].terminator().successors();
let Some(first_successor) = successors.next() else { return true };
if successors.next().is_some() {
return true;
if allowed_variants.contains(&val) {
reachable_count += 1;
} else {
removable_switchs.push((bb, index));
}
if let TerminatorKind::SwitchInt { .. } =
&basic_blocks[first_successor].terminator().kind
{
return false;
};
true
}
let otherwise_is_last_variant = !otherwise_is_empty_unreachable
&& allowed_variants.len() == 1
&& check_successors(&body.basic_blocks, targets.otherwise());
let replace_otherwise_to_unreachable = otherwise_is_last_variant
|| !otherwise_is_empty_unreachable && allowed_variants.is_empty();

if unreachable_targets.is_empty() && !replace_otherwise_to_unreachable {
continue;
if reachable_count == allowed_variants.len() {
removable_switchs.push((bb, targets.iter().count()));
}
}

let unreachable_block = patch.unreachable_no_cleanup_block();
let mut targets = targets.clone();
if replace_otherwise_to_unreachable {
if otherwise_is_last_variant {
#[allow(rustc::potential_query_instability)]
let last_variant = *allowed_variants.iter().next().unwrap();
targets.add_target(last_variant, targets.otherwise());
}
unreachable_targets.push(targets.iter().count());
}
for index in unreachable_targets.iter() {
targets.all_targets_mut()[*index] = unreachable_block;
}
patch.patch_terminator(bb, TerminatorKind::SwitchInt { targets, discr: discr.clone() });
if removable_switchs.is_empty() {
return;
}

patch.apply(body);
let new_block = BasicBlockData::new(Some(Terminator {
source_info: body.basic_blocks[removable_switchs[0].0].terminator().source_info,
kind: TerminatorKind::Unreachable,
}));
let unreachable_block = body.basic_blocks.as_mut().push(new_block);

for (bb, index) in removable_switchs {
let bb = &mut body.basic_blocks.as_mut()[bb];
let terminator = bb.terminator_mut();
let TerminatorKind::SwitchInt { targets, .. } = &mut terminator.kind else { bug!() };
targets.all_targets_mut()[index] = unreachable_block;
}
}
}
24 changes: 0 additions & 24 deletions tests/codegen/enum/uninhabited_enum_default_branch.rs
View file

This file was deleted.

6 changes: 1 addition & 5 deletions tests/mir-opt/funky_arms.float_to_exponential_common.GVN.panic-abort.diff
View file
Expand Up @@ -69,7 +69,7 @@
StorageLive(_6);
_6 = ((*_1).4: std::option::Option<usize>);
_7 = discriminant(_6);
switchInt(move _7) -> [1: bb4, 0: bb6, otherwise: bb9];
switchInt(move _7) -> [1: bb4, otherwise: bb6];
}

bb4: {
Expand Down Expand Up @@ -135,9 +135,5 @@
StorageDead(_6);
return;
}

bb9: {
unreachable;
}
}

6 changes: 1 addition & 5 deletions tests/mir-opt/funky_arms.float_to_exponential_common.GVN.panic-unwind.diff
View file
Expand Up @@ -69,7 +69,7 @@
StorageLive(_6);
_6 = ((*_1).4: std::option::Option<usize>);
_7 = discriminant(_6);
switchInt(move _7) -> [1: bb4, 0: bb6, otherwise: bb9];
switchInt(move _7) -> [1: bb4, otherwise: bb6];
}

bb4: {
Expand Down Expand Up @@ -135,9 +135,5 @@
StorageDead(_6);
return;
}

bb9: {
unreachable;
}
}

22 changes: 10 additions & 12 deletions tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-abort.mir
View file
Expand Up @@ -33,21 +33,21 @@ fn num_to_digit(_1: char) -> u32 {
_3 = &_2;
StorageLive(_4);
_4 = discriminant(_2);
switchInt(move _4) -> [1: bb2, 0: bb6, otherwise: bb8];
StorageDead(_3);
StorageDead(_2);
switchInt(move _4) -> [1: bb2, otherwise: bb7];
}

bb2: {
StorageDead(_4);
StorageDead(_3);
StorageDead(_2);
StorageLive(_5);
_5 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind unreachable];
}

bb3: {
StorageLive(_6);
_6 = discriminant(_5);
switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb8];
switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb6];
}

bb4: {
Expand All @@ -58,22 +58,20 @@ fn num_to_digit(_1: char) -> u32 {
_0 = move ((_5 as Some).0: u32);
StorageDead(_6);
StorageDead(_5);
goto -> bb7;
goto -> bb8;
}

bb6: {
StorageDead(_4);
StorageDead(_3);
StorageDead(_2);
_0 = const 0_u32;
goto -> bb7;
unreachable;
}

bb7: {
return;
StorageDead(_4);
_0 = const 0_u32;
goto -> bb8;
}

bb8: {
unreachable;
return;
}
}
22 changes: 10 additions & 12 deletions tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-unwind.mir
View file
Expand Up @@ -33,21 +33,21 @@ fn num_to_digit(_1: char) -> u32 {
_3 = &_2;
StorageLive(_4);
_4 = discriminant(_2);
switchInt(move _4) -> [1: bb2, 0: bb6, otherwise: bb8];
StorageDead(_3);
StorageDead(_2);
switchInt(move _4) -> [1: bb2, otherwise: bb7];
}

bb2: {
StorageDead(_4);
StorageDead(_3);
StorageDead(_2);
StorageLive(_5);
_5 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind continue];
}

bb3: {
StorageLive(_6);
_6 = discriminant(_5);
switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb8];
switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb6];
}

bb4: {
Expand All @@ -58,22 +58,20 @@ fn num_to_digit(_1: char) -> u32 {
_0 = move ((_5 as Some).0: u32);
StorageDead(_6);
StorageDead(_5);
goto -> bb7;
goto -> bb8;
}

bb6: {
StorageDead(_4);
StorageDead(_3);
StorageDead(_2);
_0 = const 0_u32;
goto -> bb7;
unreachable;
}

bb7: {
return;
StorageDead(_4);
_0 = const 0_u32;
goto -> bb8;
}

bb8: {
unreachable;
return;
}
}

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