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Always enable MultipleReturnTerminators #106362

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68abf63
Always enable MultipleReturnTerminators
saethlin Jan 2, 2023
8ac5850
Bless
saethlin Jan 2, 2023
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13 changes: 8 additions & 5 deletions compiler/rustc_mir_transform/src/multiple_return_terminators.rs
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Expand Up @@ -9,10 +9,6 @@ use rustc_middle::ty::TyCtxt;
pub struct MultipleReturnTerminators;

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

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// find basic blocks with no statement and a return terminator
let mut bbs_simple_returns = BitSet::new_empty(body.basic_blocks.len());
Expand All @@ -26,6 +22,10 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
}
}

// This pass usually doesn't fire, but when it does we want to remove any dead blocks it
// creates. So we only look for dead blocks if it does anything.
let mut optimized = false;

for bb in bbs {
if !tcx.consider_optimizing(|| format!("MultipleReturnTerminators {:?} ", def_id)) {
break;
Expand All @@ -34,10 +34,13 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
if let TerminatorKind::Goto { target } = bb.terminator().kind {
if bbs_simple_returns.contains(target) {
bb.terminator_mut().kind = TerminatorKind::Return;
optimized = true;
}
}
}

simplify::remove_dead_blocks(tcx, body)
if optimized {
simplify::remove_dead_blocks(tcx, body)
}
}
}
8 changes: 2 additions & 6 deletions src/test/mir-opt/76803_regression.encode.SimplifyBranchSame.diff
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Expand Up @@ -13,17 +13,13 @@

bb1: {
_0 = move _1; // scope 0 at $DIR/76803_regression.rs:+3:14: +3:15
goto -> bb3; // scope 0 at $DIR/76803_regression.rs:+3:14: +3:15
return; // scope 0 at $DIR/76803_regression.rs:+3:14: +3:15
}

bb2: {
Deinit(_0); // scope 0 at $DIR/76803_regression.rs:+2:20: +2:27
discriminant(_0) = 1; // scope 0 at $DIR/76803_regression.rs:+2:20: +2:27
goto -> bb3; // scope 0 at $DIR/76803_regression.rs:+2:20: +2:27
}

bb3: {
return; // scope 0 at $DIR/76803_regression.rs:+5:2: +5:2
return; // scope 0 at $DIR/76803_regression.rs:+2:20: +2:27
}
}

6 changes: 1 addition & 5 deletions src/test/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.diff
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Expand Up @@ -98,7 +98,7 @@
StorageDead(_33); // scope 0 at $DIR/early_otherwise_branch_68867.rs:+10:27: +10:28
StorageDead(_3); // scope 0 at $DIR/early_otherwise_branch_68867.rs:+11:6: +11:7
StorageDead(_4); // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:1: +12:2
goto -> bb11; // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:2: +12:2
return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:2: +12:2
}

bb3: {
Expand Down Expand Up @@ -221,10 +221,6 @@
discriminant(_0) = 0; // scope 0 at $DIR/early_otherwise_branch_68867.rs:+5:5: +11:7
StorageDead(_3); // scope 0 at $DIR/early_otherwise_branch_68867.rs:+11:6: +11:7
StorageDead(_4); // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:1: +12:2
goto -> bb11; // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:2: +12:2
}

bb11: {
return; // scope 0 at $DIR/early_otherwise_branch_68867.rs:+12:2: +12:2
}
}
Expand Down
10 changes: 3 additions & 7 deletions src/test/mir-opt/early_otherwise_branch_soundness.no_deref_ptr.EarlyOtherwiseBranch.diff
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Expand Up @@ -19,7 +19,7 @@

bb1: {
_0 = const 0_i32; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+7:14: +7:15
goto -> bb5; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+7:14: +7:15
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+7:14: +7:15
}

bb2: {
Expand All @@ -29,19 +29,15 @@

bb3: {
_0 = const 0_i32; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+5:18: +5:19
goto -> bb5; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+5:18: +5:19
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+5:18: +5:19
}

bb4: {
StorageLive(_5); // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+4:18: +4:19
_5 = (((*_2) as Some).0: i32); // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+4:18: +4:19
_0 = _5; // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+4:24: +4:25
StorageDead(_5); // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+4:24: +4:25
goto -> bb5; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+4:24: +4:25
}

bb5: {
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+9:2: +9:2
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+4:24: +4:25
}
}

8 changes: 2 additions & 6 deletions src/test/mir-opt/early_otherwise_branch_soundness.no_downcast.EarlyOtherwiseBranch.diff
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Expand Up @@ -23,16 +23,12 @@

bb2: {
_0 = const 1_u32; // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+1:38: +1:39
goto -> bb4; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:5: +1:52
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:5: +1:52
}

bb3: {
_0 = const 2_u32; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:49: +1:50
goto -> bb4; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:5: +1:52
}

bb4: {
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+2:2: +2:2
return; // scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:5: +1:52
}
}

18 changes: 7 additions & 11 deletions src/test/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.mir
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Expand Up @@ -31,7 +31,7 @@ fn num_to_digit(_1: char) -> u32 {
StorageLive(_5); // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
StorageLive(_6); // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
_6 = _1; // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
_5 = char::methods::<impl char>::to_digit(move _6, const 8_u32) -> bb5; // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
_5 = char::methods::<impl char>::to_digit(move _6, const 8_u32) -> bb4; // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
// mir::Constant
// + span: $SRC_DIR/core/src/char/methods.rs:LL:COL
// + literal: Const { ty: fn(char, u32) -> Option<u32> {char::methods::<impl char>::to_digit}, val: Value(<ZST>) }
Expand All @@ -47,19 +47,15 @@ fn num_to_digit(_1: char) -> u32 {

bb2: {
_7 = discriminant(_2); // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
switchInt(move _7) -> [0: bb6, 1: bb8, otherwise: bb7]; // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
switchInt(move _7) -> [0: bb5, 1: bb7, otherwise: bb6]; // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
}

bb3: {
_0 = const 0_u32; // scope 0 at $DIR/issue_59352.rs:+2:60: +2:61
goto -> bb4; // scope 0 at $DIR/issue_59352.rs:+2:5: +2:63
return; // scope 0 at $DIR/issue_59352.rs:+2:5: +2:63
}

bb4: {
return; // scope 0 at $DIR/issue_59352.rs:+3:2: +3:2
}

bb5: {
_4 = &_5; // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
StorageDead(_6); // scope 1 at $SRC_DIR/core/src/char/methods.rs:LL:COL
_9 = discriminant((*_4)); // scope 2 at $SRC_DIR/core/src/option.rs:LL:COL
Expand All @@ -69,7 +65,7 @@ fn num_to_digit(_1: char) -> u32 {
switchInt(move _9) -> [1: bb1, otherwise: bb3]; // scope 0 at $DIR/issue_59352.rs:+2:8: +2:23
}

bb6: {
bb5: {
StorageLive(_8); // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
_8 = core::panicking::panic(const "called `Option::unwrap()` on a `None` value"); // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
// mir::Constant
Expand All @@ -80,13 +76,13 @@ fn num_to_digit(_1: char) -> u32 {
// + literal: Const { ty: &str, val: Value(Slice(..)) }
}

bb7: {
bb6: {
unreachable; // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
}

bb8: {
bb7: {
_0 = move ((_2 as Some).0: u32); // scope 3 at $SRC_DIR/core/src/option.rs:LL:COL
StorageDead(_2); // scope 0 at $DIR/issue_59352.rs:+2:49: +2:50
goto -> bb4; // scope 0 at $DIR/issue_59352.rs:+2:5: +2:63
return; // scope 0 at $DIR/issue_59352.rs:+2:5: +2:63
}
}
4 changes: 2 additions & 2 deletions src/test/mir-opt/separate_const_switch.identity.SeparateConstSwitch.diff
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Expand Up @@ -115,7 +115,7 @@
discriminant(_3) = 1; // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_14); // scope 7 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_13); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
- goto -> bb1; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
- goto -> bb1; // scope 0 at $SRC_DIR/core/src/result.rs:LL:COL
+ StorageDead(_4); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
+ _5 = discriminant(_3); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
+ switchInt(move _5) -> [0: bb1, 1: bb3, otherwise: bb2]; // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
Expand All @@ -137,7 +137,7 @@
discriminant(_3) = 0; // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_12); // scope 6 at $SRC_DIR/core/src/result.rs:LL:COL
StorageDead(_11); // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
- goto -> bb1; // scope 5 at $SRC_DIR/core/src/result.rs:LL:COL
- goto -> bb1; // scope 0 at $SRC_DIR/core/src/result.rs:LL:COL
+ StorageDead(_4); // scope 0 at $DIR/separate_const_switch.rs:+1:9: +1:10
+ _5 = discriminant(_3); // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
+ switchInt(move _5) -> [0: bb1, 1: bb3, otherwise: bb2]; // scope 0 at $DIR/separate_const_switch.rs:+1:8: +1:10
Expand Down