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Auto merge of #93387 - JakobDegen:improve_partialeq, r=tmiasko

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Extend uninhabited enum variant branch elimination to also affect fallthrough

The `uninhabited_enum_branching` mir opt eliminates branches on variants where the data is uninhabited. This change extends this pass to also ensure that the `otherwise` case points to a trivially unreachable bb if all inhabited variants are present in the non-otherwise branches.

I believe it was `@scottmcm` who said that LLVM eliminates some of this information in its SimplifyCFG pass. This is unfortunate, but this change should still be at least a small improvement in principle (I don't think it will show up on any benchmarks)
This commit is contained in:
bors 2022-02-20 05:24:52 +00:00
commit a6fe969541
7 changed files with 167 additions and 20 deletions
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42
compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
View File

@ -3,7 +3,8 @@
use crate::MirPass;
use rustc_data_structures::stable_set::FxHashSet;
use rustc_middle::mir::{
BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, SwitchTargets, TerminatorKind,
BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, SwitchTargets, Terminator,
TerminatorKind,
};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{Ty, TyCtxt};
@ -71,6 +72,28 @@ fn variant_discriminants<'tcx>(
}
}
/// Ensures that the `otherwise` branch leads to an unreachable bb, returning `None` if so and a new
/// bb to use as the new target if not.
fn ensure_otherwise_unreachable<'tcx>(
body: &Body<'tcx>,
targets: &SwitchTargets,
) -> Option<BasicBlockData<'tcx>> {
let otherwise = targets.otherwise();
let bb = &body.basic_blocks()[otherwise];
if bb.terminator().kind == TerminatorKind::Unreachable
&& bb.statements.iter().all(|s| matches!(&s.kind, StatementKind::StorageDead(_)))
{
return None;
}
let mut new_block = BasicBlockData::new(Some(Terminator {
source_info: bb.terminator().source_info,
kind: TerminatorKind::Unreachable,
}));
new_block.is_cleanup = bb.is_cleanup;
Some(new_block)
}
impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() > 0
@ -99,12 +122,25 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
if let TerminatorKind::SwitchInt { targets, .. } =
&mut body.basic_blocks_mut()[bb].terminator_mut().kind
{
let new_targets = SwitchTargets::new(
let mut new_targets = SwitchTargets::new(
targets.iter().filter(|(val, _)| allowed_variants.contains(val)),
targets.otherwise(),
);
*targets = new_targets;
if new_targets.iter().count() == allowed_variants.len() {
if let Some(updated) = ensure_otherwise_unreachable(body, &new_targets) {
let new_otherwise = body.basic_blocks_mut().push(updated);
*new_targets.all_targets_mut().last_mut().unwrap() = new_otherwise;
}
}
if let TerminatorKind::SwitchInt { targets, .. } =
&mut body.basic_blocks_mut()[bb].terminator_mut().kind
{
*targets = new_targets;
} else {
unreachable!()
}
} else {
unreachable!()
}

8
src/test/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff
View File

@ -31,7 +31,7 @@
StorageDead(_5); // scope 0 at $DIR/early_otherwise_branch.rs:12:16: 12:17
StorageDead(_4); // scope 0 at $DIR/early_otherwise_branch.rs:12:16: 12:17
_8 = discriminant((_3.0: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:12:11: 12:17
- switchInt(move _8) -> [0_isize: bb1, 1_isize: bb3, otherwise: bb2]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
- switchInt(move _8) -> [0_isize: bb1, 1_isize: bb3, otherwise: bb7]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
+ StorageLive(_11); // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
+ _11 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
+ StorageLive(_12); // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
@ -81,8 +81,10 @@
+ bb4: {
StorageDead(_3); // scope 0 at $DIR/early_otherwise_branch.rs:17:1: 17:2
return; // scope 0 at $DIR/early_otherwise_branch.rs:17:2: 17:2
+ }
+
}
- bb7: {
- unreachable; // scope 0 at $DIR/early_otherwise_branch.rs:15:14: 15:15
+ bb5: {
+ StorageDead(_12); // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
+ switchInt(_8) -> [0_isize: bb3, 1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17

25
src/test/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.before-SimplifyConstCondition-final.after.diff
View File

@ -81,7 +81,7 @@
- StorageDead(_5); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:23: 21:24
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:23: 21:24
_11 = discriminant((*(_4.0: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:14: 21:24
- switchInt(move _11) -> [0_isize: bb1, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb2]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
- switchInt(move _11) -> [0_isize: bb1, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb11]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ StorageLive(_34); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ _34 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ StorageLive(_35); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
@ -217,14 +217,9 @@
- StorageDead(_13); // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:49: 22:50
- StorageDead(_12); // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:49: 22:50
- goto -> bb10; // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:49: 22:50
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
+ discriminant(_0) = 0; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:27:6: 27:7
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:1: 28:2
+ return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
}
bb7: {
- }
-
- bb7: {
- StorageLive(_17); // scope 0 at $DIR/early_otherwise_branch_68867.rs:23:14: 23:17
- _17 = (((*(_4.0: &ViewportPercentageLength)) as Vh).0: f32); // scope 0 at $DIR/early_otherwise_branch_68867.rs:23:14: 23:17
- StorageLive(_18); // scope 0 at $DIR/early_otherwise_branch_68867.rs:23:24: 23:29
@ -289,10 +284,18 @@
-
- bb10: {
- ((_0 as Ok).0: ViewportPercentageLength) = move _3; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
- discriminant(_0) = 0; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
discriminant(_0) = 0; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:5: 27:7
- StorageDead(_3); // scope 0 at $DIR/early_otherwise_branch_68867.rs:27:6: 27:7
- StorageDead(_4); // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:1: 28:2
- return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:27:6: 27:7
+ nop; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:1: 28:2
return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
}
- bb11: {
- unreachable; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
+ bb7: {
+ StorageDead(_35); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
}

8
src/test/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.diff
View File

@ -67,7 +67,7 @@
StorageDead(_6); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:23: 21:24
StorageDead(_5); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:23: 21:24
_11 = discriminant((*(_4.0: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:14: 21:24
- switchInt(move _11) -> [0_isize: bb1, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb2]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
- switchInt(move _11) -> [0_isize: bb1, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb11]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ StorageLive(_34); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ _34 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ StorageLive(_35); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
@ -206,8 +206,10 @@
StorageDead(_3); // scope 0 at $DIR/early_otherwise_branch_68867.rs:27:6: 27:7
StorageDead(_4); // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:1: 28:2
return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
+ }
+
}
- bb11: {
- unreachable; // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
+ bb7: {
+ StorageDead(_35); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
+ switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24

38
src/test/mir-opt/uninhabited_fallthrough_elimination.eliminate_fallthrough.UninhabitedEnumBranching.diff Normal file
View File

@ -0,0 +1,38 @@
- // MIR for `eliminate_fallthrough` before UninhabitedEnumBranching
+ // MIR for `eliminate_fallthrough` after UninhabitedEnumBranching
fn eliminate_fallthrough(_1: S) -> u32 {
debug s => _1; // in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:21:26: 21:27
let mut _0: u32; // return place in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:21:35: 21:38
let mut _2: isize; // in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:23:9: 23:10
bb0: {
_2 = discriminant(_1); // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:22:11: 22:12
- switchInt(move _2) -> [1_isize: bb3, 2_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:22:5: 22:12
+ switchInt(move _2) -> [1_isize: bb3, 2_isize: bb2, otherwise: bb5]; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:22:5: 22:12
}
bb1: {
_0 = const 3_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:25:14: 25:15
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:25:14: 25:15
}
bb2: {
_0 = const 1_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:23:14: 23:15
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:23:14: 23:15
}
bb3: {
_0 = const 2_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:24:14: 24:15
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:24:14: 24:15
}
bb4: {
return; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:27:2: 27:2
+ }
+
+ bb5: {
+ unreachable; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:25:14: 25:15
}
}

34
src/test/mir-opt/uninhabited_fallthrough_elimination.keep_fallthrough.UninhabitedEnumBranching.diff Normal file
View File

@ -0,0 +1,34 @@
- // MIR for `keep_fallthrough` before UninhabitedEnumBranching
+ // MIR for `keep_fallthrough` after UninhabitedEnumBranching
fn keep_fallthrough(_1: S) -> u32 {
debug s => _1; // in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:12:21: 12:22
let mut _0: u32; // return place in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:12:30: 12:33
let mut _2: isize; // in scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:14:9: 14:13
bb0: {
_2 = discriminant(_1); // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:13:11: 13:12
- switchInt(move _2) -> [0_isize: bb2, 1_isize: bb3, otherwise: bb1]; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:13:5: 13:12
+ switchInt(move _2) -> [1_isize: bb3, otherwise: bb1]; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:13:5: 13:12
}
bb1: {
_0 = const 3_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:16:14: 16:15
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:16:14: 16:15
}
bb2: {
_0 = const 1_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:14:17: 14:18
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:14:17: 14:18
}
bb3: {
_0 = const 2_u32; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:15:14: 15:15
goto -> bb4; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:15:14: 15:15
}
bb4: {
return; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:18:2: 18:2
}
}

32
src/test/mir-opt/uninhabited_fallthrough_elimination.rs Normal file
View File

@ -0,0 +1,32 @@
enum Empty {}
enum S {
A(Empty),
B,
C,
}
use S::*;
// EMIT_MIR uninhabited_fallthrough_elimination.keep_fallthrough.UninhabitedEnumBranching.diff
fn keep_fallthrough(s: S) -> u32 {
match s {
A(_) => 1,
B => 2,
_ => 3,
}
}
// EMIT_MIR uninhabited_fallthrough_elimination.eliminate_fallthrough.UninhabitedEnumBranching.diff
fn eliminate_fallthrough(s: S) -> u32 {
match s {
C => 1,
B => 2,
_ => 3,
}
}
fn main() {
keep_fallthrough(B);
eliminate_fallthrough(B);
}