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Auto merge of rust-lang#112040 - cjgillot:separate-const-switch, r=ol…
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…i-obk

Enable ConstGoto and SeparateConstSwitch passes by default

These 2 passes implement a limited form of jump-threading.
Filing this PR to see if enabling them would be lighter than rust-lang#107009.
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@bors
bors committed Jun 1, 2023
2 parents 642c92e + f74695b commit 789dd0b
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Showing 6 changed files with 62 additions and 84 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_mir_transform/src/const_goto.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ pub struct ConstGoto;

impl<'tcx> MirPass<'tcx> for ConstGoto {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() >= 4
sess.mir_opt_level() >= 2
}

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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38 changes: 24 additions & 14 deletions compiler/rustc_mir_transform/src/const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,14 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
// That would require a uniform one-def no-mutation analysis
// and RPO (or recursing when needing the value of a local).
let mut optimization_finder = ConstPropagator::new(body, dummy_body, tcx);
optimization_finder.visit_body(body);

// Traverse the body in reverse post-order, to ensure that `FullConstProp` locals are
// assigned before being read.
let postorder = body.basic_blocks.postorder().to_vec();
for bb in postorder.into_iter().rev() {
let data = &mut body.basic_blocks.as_mut_preserves_cfg()[bb];
optimization_finder.visit_basic_block_data(bb, data);
}

trace!("ConstProp done for {:?}", def_id);
}
Expand Down Expand Up @@ -789,12 +796,6 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
self.tcx
}

fn visit_body(&mut self, body: &mut Body<'tcx>) {
for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
self.visit_basic_block_data(bb, data);
}
}

fn visit_operand(&mut self, operand: &mut Operand<'tcx>, location: Location) {
self.super_operand(operand, location);

Expand Down Expand Up @@ -885,14 +886,23 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
}
}
StatementKind::StorageLive(local) => {
let frame = self.ecx.frame_mut();
frame.locals[local].value =
LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit));
}
StatementKind::StorageDead(local) => {
let frame = self.ecx.frame_mut();
frame.locals[local].value = LocalValue::Dead;
Self::remove_const(&mut self.ecx, local);
}
// We do not need to mark dead locals as such. For `FullConstProp` locals,
// this allows to propagate the single assigned value in this case:
// ```
// let x = SOME_CONST;
// if a {
// f(copy x);
// StorageDead(x);
// } else {
// g(copy x);
// StorageDead(x);
// }
// ```
//
// This may propagate a constant where the local would be uninit or dead.
// In both cases, this does not matter, as those reads would be UB anyway.
_ => {}
}
}
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5 changes: 4 additions & 1 deletion compiler/rustc_mir_transform/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -559,10 +559,13 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// inst combine is after MatchBranchSimplification to clean up Ne(_1, false)
&multiple_return_terminators::MultipleReturnTerminators,
&instsimplify::InstSimplify,
&separate_const_switch::SeparateConstSwitch,
&simplify::SimplifyLocals::BeforeConstProp,
&copy_prop::CopyProp,
&ref_prop::ReferencePropagation,
// Perform `SeparateConstSwitch` after SSA-based analyses, as cloning blocks may
// destroy the SSA property. It should still happen before const-propagation, so the
// latter pass will leverage the created opportunities.
&separate_const_switch::SeparateConstSwitch,
&const_prop::ConstProp,
&dataflow_const_prop::DataflowConstProp,
//
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2 changes: 1 addition & 1 deletion compiler/rustc_mir_transform/src/separate_const_switch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,7 @@ pub struct SeparateConstSwitch;

impl<'tcx> MirPass<'tcx> for SeparateConstSwitch {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() >= 4
sess.mir_opt_level() >= 2
}

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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78 changes: 29 additions & 49 deletions tests/mir-opt/separate_const_switch.identity.SeparateConstSwitch.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -9,70 +9,61 @@
let mut _4: std::result::Result<i32, i32>; // in scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:9
let mut _5: isize; // in scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
let _6: std::result::Result<std::convert::Infallible, i32>; // in scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
let mut _7: !; // in scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
let mut _8: std::result::Result<std::convert::Infallible, i32>; // in scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
let _9: i32; // in scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
let mut _7: std::result::Result<std::convert::Infallible, i32>; // in scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
let _8: i32; // in scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
scope 1 {
debug residual => _6; // in scope 1 at $DIR/separate_const_switch.rs:+1:9: +1:10
scope 2 {
scope 8 (inlined #[track_caller] <Result<i32, i32> as FromResidual<Result<Infallible, i32>>>::from_residual) { // at $DIR/separate_const_switch.rs:25:8: 25:10
debug residual => _8; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
let _14: i32; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _15: i32; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
debug residual => _6; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
let _13: i32; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _14: i32; // in scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
scope 9 {
debug e => _14; // in scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
debug e => _13; // in scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
scope 10 (inlined <i32 as From<i32>>::from) { // at $SRC_DIR/core/src/result.rs:LL:COL
debug t => _14; // in scope 10 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
debug t => _13; // in scope 10 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
}
}
}
}
}
scope 3 {
debug val => _9; // in scope 3 at $DIR/separate_const_switch.rs:+1:8: +1:10
debug val => _8; // in scope 3 at $DIR/separate_const_switch.rs:+1:8: +1:10
scope 4 {
}
}
scope 5 (inlined <Result<i32, i32> as Try>::branch) { // at $DIR/separate_const_switch.rs:25:8: 25:10
debug self => _4; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _10: isize; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
debug self => _1; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _9: isize; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let _10: i32; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let _11: i32; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let _12: i32; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _13: std::result::Result<std::convert::Infallible, i32>; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
let mut _12: std::result::Result<std::convert::Infallible, i32>; // in scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
scope 6 {
debug v => _11; // in scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
debug v => _10; // in scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
}
scope 7 {
debug e => _12; // in scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
debug e => _11; // in scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
}
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageLive(_3); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageLive(_4); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:9
_4 = _1; // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:9
StorageLive(_10); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageLive(_11); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageLive(_12); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
_10 = discriminant(_4); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
switchInt(move _10) -> [0: bb7, 1: bb5, otherwise: bb6]; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
_9 = discriminant(_1); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
switchInt(move _9) -> [0: bb7, 1: bb5, otherwise: bb6]; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
}

bb1: {
StorageDead(_12); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageDead(_11); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageDead(_4); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
StorageDead(_10); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
_5 = discriminant(_3); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
switchInt(move _5) -> [0: bb2, 1: bb4, otherwise: bb3]; // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
}

bb2: {
StorageLive(_9); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
_9 = ((_3 as Continue).0: i32); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
_2 = _9; // scope 4 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageDead(_9); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
_0 = Result::<i32, i32>::Ok(move _2); // scope 0 at $DIR/separate_const_switch.rs:+1:5: +1:11
StorageDead(_2); // scope 0 at $DIR/separate_const_switch.rs:+1:10: +1:11
_8 = ((_3 as Continue).0: i32); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
_0 = Result::<i32, i32>::Ok(_8); // scope 0 at $DIR/separate_const_switch.rs:+1:5: +1:11
StorageDead(_3); // scope 0 at $DIR/separate_const_switch.rs:+2:1: +2:2
return; // scope 0 at $DIR/separate_const_switch.rs:+2:2: +2:2
}
Expand All @@ -82,30 +73,19 @@
}

bb4: {
StorageLive(_6); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
_6 = ((_3 as Break).0: std::result::Result<std::convert::Infallible, i32>); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
StorageLive(_8); // scope 2 at $DIR/separate_const_switch.rs:+1:9: +1:10
_8 = _6; // scope 2 at $DIR/separate_const_switch.rs:+1:9: +1:10
StorageLive(_14); // scope 2 at $DIR/separate_const_switch.rs:+1:8: +1:10
_14 = move ((_8 as Err).0: i32); // scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
StorageLive(_15); // scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
_15 = move _14; // scope 10 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_0 = Result::<i32, i32>::Err(move _15); // scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_15); // scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_14); // scope 2 at $DIR/separate_const_switch.rs:+1:8: +1:10
StorageDead(_8); // scope 2 at $DIR/separate_const_switch.rs:+1:9: +1:10
StorageDead(_6); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
StorageDead(_2); // scope 0 at $DIR/separate_const_switch.rs:+1:10: +1:11
_13 = ((_6 as Err).0: i32); // scope 8 at $SRC_DIR/core/src/result.rs:LL:COL
_0 = Result::<i32, i32>::Err(move _13); // scope 9 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_3); // scope 0 at $DIR/separate_const_switch.rs:+2:1: +2:2
return; // scope 0 at $DIR/separate_const_switch.rs:+2:2: +2:2
}

bb5: {
_12 = move ((_4 as Err).0: i32); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
StorageLive(_13); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
_13 = Result::<Infallible, i32>::Err(move _12); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
_3 = ControlFlow::<Result<Infallible, i32>, i32>::Break(move _13); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_13); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
_11 = ((_1 as Err).0: i32); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
StorageLive(_12); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
_12 = Result::<Infallible, i32>::Err(move _11); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
_3 = ControlFlow::<Result<Infallible, i32>, i32>::Break(move _12); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_12); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
goto -> bb1; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
}

Expand All @@ -114,8 +94,8 @@
}

bb7: {
_11 = move ((_4 as Ok).0: i32); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
_3 = ControlFlow::<Result<Infallible, i32>, i32>::Continue(move _11); // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
_10 = ((_1 as Ok).0: i32); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
_3 = ControlFlow::<Result<Infallible, i32>, i32>::Continue(move _10); // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
goto -> bb1; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
}
}
Expand Down
21 changes: 3 additions & 18 deletions tests/mir-opt/separate_const_switch.too_complex.SeparateConstSwitch.diff
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,13 +34,8 @@
}

bb1: {
StorageLive(_6); // scope 0 at $DIR/separate_const_switch.rs:+8:17: +8:18
_6 = ((_1 as Err).0: usize); // scope 0 at $DIR/separate_const_switch.rs:+8:17: +8:18
StorageLive(_7); // scope 2 at $DIR/separate_const_switch.rs:+8:42: +8:43
_7 = _6; // scope 2 at $DIR/separate_const_switch.rs:+8:42: +8:43
_2 = ControlFlow::<usize, i32>::Break(move _7); // scope 2 at $DIR/separate_const_switch.rs:+8:23: +8:44
StorageDead(_7); // scope 2 at $DIR/separate_const_switch.rs:+8:43: +8:44
StorageDead(_6); // scope 0 at $DIR/separate_const_switch.rs:+8:43: +8:44
_2 = ControlFlow::<usize, i32>::Break(_6); // scope 2 at $DIR/separate_const_switch.rs:+8:23: +8:44
goto -> bb4; // scope 0 at $DIR/separate_const_switch.rs:+8:43: +8:44
}

Expand All @@ -49,13 +44,8 @@
}

bb3: {
StorageLive(_4); // scope 0 at $DIR/separate_const_switch.rs:+7:16: +7:17
_4 = ((_1 as Ok).0: i32); // scope 0 at $DIR/separate_const_switch.rs:+7:16: +7:17
StorageLive(_5); // scope 1 at $DIR/separate_const_switch.rs:+7:44: +7:45
_5 = _4; // scope 1 at $DIR/separate_const_switch.rs:+7:44: +7:45
_2 = ControlFlow::<usize, i32>::Continue(move _5); // scope 1 at $DIR/separate_const_switch.rs:+7:22: +7:46
StorageDead(_5); // scope 1 at $DIR/separate_const_switch.rs:+7:45: +7:46
StorageDead(_4); // scope 0 at $DIR/separate_const_switch.rs:+7:45: +7:46
_2 = ControlFlow::<usize, i32>::Continue(_4); // scope 1 at $DIR/separate_const_switch.rs:+7:22: +7:46
goto -> bb4; // scope 0 at $DIR/separate_const_switch.rs:+7:45: +7:46
}

Expand All @@ -73,13 +63,8 @@
}

bb6: {
StorageLive(_9); // scope 0 at $DIR/separate_const_switch.rs:+11:31: +11:32
_9 = ((_2 as Continue).0: i32); // scope 0 at $DIR/separate_const_switch.rs:+11:31: +11:32
StorageLive(_10); // scope 3 at $DIR/separate_const_switch.rs:+11:42: +11:43
_10 = _9; // scope 3 at $DIR/separate_const_switch.rs:+11:42: +11:43
_0 = Option::<i32>::Some(move _10); // scope 3 at $DIR/separate_const_switch.rs:+11:37: +11:44
StorageDead(_10); // scope 3 at $DIR/separate_const_switch.rs:+11:43: +11:44
StorageDead(_9); // scope 0 at $DIR/separate_const_switch.rs:+11:43: +11:44
_0 = Option::<i32>::Some(_9); // scope 3 at $DIR/separate_const_switch.rs:+11:37: +11:44
goto -> bb7; // scope 0 at $DIR/separate_const_switch.rs:+11:43: +11:44
}

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