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Disable MatchBranchSimplification
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This optimization can result in unsoundness, because it introduces
additional uses of a place holding the discriminant value without
ensuring that it is valid to do so.
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@tmiasko @Mark-Simulacrum
tmiasko authored and Mark-Simulacrum committed Nov 6, 2020
1 parent 83dd706 commit 49c5862
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Showing 7 changed files with 179 additions and 150 deletions.
7 changes: 7 additions & 0 deletions compiler/rustc_mir/src/transform/match_branches.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,13 @@ pub struct MatchBranchSimplification;

impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, body: &mut Body<'tcx>) {
// FIXME: This optimization can result in unsoundness, because it introduces
// additional uses of a place holding the discriminant value without ensuring that
// it is valid to do so.
if !tcx.sess.opts.debugging_opts.unsound_mir_opts {
return;
}

let param_env = tcx.param_env(src.def_id());
let bbs = body.basic_blocks_mut();
'outer: for bb_idx in bbs.indices() {
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116 changes: 58 additions & 58 deletions src/test/mir-opt/matches_reduce_branches.bar.MatchBranchSimplification.32bit.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -2,83 +2,83 @@
+ // MIR for `bar` after MatchBranchSimplification

fn bar(_1: i32) -> (bool, bool, bool, bool) {
debug i => _1; // in scope 0 at $DIR/matches_reduce_branches.rs:11:8: 11:9
let mut _0: (bool, bool, bool, bool); // return place in scope 0 at $DIR/matches_reduce_branches.rs:11:19: 11:43
let _2: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:12:9: 12:10
let _6: (); // in scope 0 at $DIR/matches_reduce_branches.rs:17:5: 32:6
let mut _7: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:34:6: 34:7
let mut _8: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:34:9: 34:10
let mut _9: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:34:12: 34:13
let mut _10: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:34:15: 34:16
debug i => _1; // in scope 0 at $DIR/matches_reduce_branches.rs:12:8: 12:9
let mut _0: (bool, bool, bool, bool); // return place in scope 0 at $DIR/matches_reduce_branches.rs:12:19: 12:43
let _2: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:13:9: 13:10
let _6: (); // in scope 0 at $DIR/matches_reduce_branches.rs:18:5: 33:6
let mut _7: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:35:6: 35:7
let mut _8: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:35:9: 35:10
let mut _9: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:35:12: 35:13
let mut _10: bool; // in scope 0 at $DIR/matches_reduce_branches.rs:35:15: 35:16
scope 1 {
debug a => _2; // in scope 1 at $DIR/matches_reduce_branches.rs:12:9: 12:10
let _3: bool; // in scope 1 at $DIR/matches_reduce_branches.rs:13:9: 13:10
debug a => _2; // in scope 1 at $DIR/matches_reduce_branches.rs:13:9: 13:10
let _3: bool; // in scope 1 at $DIR/matches_reduce_branches.rs:14:9: 14:10
scope 2 {
debug b => _3; // in scope 2 at $DIR/matches_reduce_branches.rs:13:9: 13:10
let _4: bool; // in scope 2 at $DIR/matches_reduce_branches.rs:14:9: 14:10
debug b => _3; // in scope 2 at $DIR/matches_reduce_branches.rs:14:9: 14:10
let _4: bool; // in scope 2 at $DIR/matches_reduce_branches.rs:15:9: 15:10
scope 3 {
debug c => _4; // in scope 3 at $DIR/matches_reduce_branches.rs:14:9: 14:10
let _5: bool; // in scope 3 at $DIR/matches_reduce_branches.rs:15:9: 15:10
debug c => _4; // in scope 3 at $DIR/matches_reduce_branches.rs:15:9: 15:10
let _5: bool; // in scope 3 at $DIR/matches_reduce_branches.rs:16:9: 16:10
scope 4 {
debug d => _5; // in scope 4 at $DIR/matches_reduce_branches.rs:15:9: 15:10
debug d => _5; // in scope 4 at $DIR/matches_reduce_branches.rs:16:9: 16:10
}
}
}
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/matches_reduce_branches.rs:12:9: 12:10
StorageLive(_3); // scope 1 at $DIR/matches_reduce_branches.rs:13:9: 13:10
StorageLive(_4); // scope 2 at $DIR/matches_reduce_branches.rs:14:9: 14:10
StorageLive(_5); // scope 3 at $DIR/matches_reduce_branches.rs:15:9: 15:10
StorageLive(_6); // scope 4 at $DIR/matches_reduce_branches.rs:17:5: 32:6
- switchInt(_1) -> [7_i32: bb2, otherwise: bb1]; // scope 4 at $DIR/matches_reduce_branches.rs:18:9: 18:10
+ _2 = Ne(_1, const 7_i32); // scope 4 at $DIR/matches_reduce_branches.rs:19:13: 19:22
+ _3 = Eq(_1, const 7_i32); // scope 4 at $DIR/matches_reduce_branches.rs:20:13: 20:21
+ _4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:21:13: 21:22
+ _5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:22:13: 22:21
+ goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:18:9: 18:10
StorageLive(_2); // scope 0 at $DIR/matches_reduce_branches.rs:13:9: 13:10
StorageLive(_3); // scope 1 at $DIR/matches_reduce_branches.rs:14:9: 14:10
StorageLive(_4); // scope 2 at $DIR/matches_reduce_branches.rs:15:9: 15:10
StorageLive(_5); // scope 3 at $DIR/matches_reduce_branches.rs:16:9: 16:10
StorageLive(_6); // scope 4 at $DIR/matches_reduce_branches.rs:18:5: 33:6
- switchInt(_1) -> [7_i32: bb2, otherwise: bb1]; // scope 4 at $DIR/matches_reduce_branches.rs:19:9: 19:10
+ _2 = Ne(_1, const 7_i32); // scope 4 at $DIR/matches_reduce_branches.rs:20:13: 20:22
+ _3 = Eq(_1, const 7_i32); // scope 4 at $DIR/matches_reduce_branches.rs:21:13: 21:21
+ _4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:22:13: 22:22
+ _5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:23:13: 23:21
+ goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:19:9: 19:10
}

bb1: {
_2 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:26:13: 26:21
_3 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:27:13: 27:22
_4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:28:13: 28:22
_5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:29:13: 29:21
goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:17:5: 32:6
_2 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:27:13: 27:21
_3 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:28:13: 28:22
_4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:29:13: 29:22
_5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:30:13: 30:21
goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:18:5: 33:6
}

bb2: {
_2 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:19:13: 19:22
_3 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:20:13: 20:21
_4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:21:13: 21:22
_5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:22:13: 22:21
goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:17:5: 32:6
_2 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:20:13: 20:22
_3 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:21:13: 21:21
_4 = const false; // scope 4 at $DIR/matches_reduce_branches.rs:22:13: 22:22
_5 = const true; // scope 4 at $DIR/matches_reduce_branches.rs:23:13: 23:21
goto -> bb3; // scope 4 at $DIR/matches_reduce_branches.rs:18:5: 33:6
}

bb3: {
StorageDead(_6); // scope 4 at $DIR/matches_reduce_branches.rs:32:6: 32:7
StorageLive(_7); // scope 4 at $DIR/matches_reduce_branches.rs:34:6: 34:7
_7 = _2; // scope 4 at $DIR/matches_reduce_branches.rs:34:6: 34:7
StorageLive(_8); // scope 4 at $DIR/matches_reduce_branches.rs:34:9: 34:10
_8 = _3; // scope 4 at $DIR/matches_reduce_branches.rs:34:9: 34:10
StorageLive(_9); // scope 4 at $DIR/matches_reduce_branches.rs:34:12: 34:13
_9 = _4; // scope 4 at $DIR/matches_reduce_branches.rs:34:12: 34:13
StorageLive(_10); // scope 4 at $DIR/matches_reduce_branches.rs:34:15: 34:16
_10 = _5; // scope 4 at $DIR/matches_reduce_branches.rs:34:15: 34:16
(_0.0: bool) = move _7; // scope 4 at $DIR/matches_reduce_branches.rs:34:5: 34:17
(_0.1: bool) = move _8; // scope 4 at $DIR/matches_reduce_branches.rs:34:5: 34:17
(_0.2: bool) = move _9; // scope 4 at $DIR/matches_reduce_branches.rs:34:5: 34:17
(_0.3: bool) = move _10; // scope 4 at $DIR/matches_reduce_branches.rs:34:5: 34:17
StorageDead(_10); // scope 4 at $DIR/matches_reduce_branches.rs:34:16: 34:17
StorageDead(_9); // scope 4 at $DIR/matches_reduce_branches.rs:34:16: 34:17
StorageDead(_8); // scope 4 at $DIR/matches_reduce_branches.rs:34:16: 34:17
StorageDead(_7); // scope 4 at $DIR/matches_reduce_branches.rs:34:16: 34:17
StorageDead(_5); // scope 3 at $DIR/matches_reduce_branches.rs:35:1: 35:2
StorageDead(_4); // scope 2 at $DIR/matches_reduce_branches.rs:35:1: 35:2
StorageDead(_3); // scope 1 at $DIR/matches_reduce_branches.rs:35:1: 35:2
StorageDead(_2); // scope 0 at $DIR/matches_reduce_branches.rs:35:1: 35:2
return; // scope 0 at $DIR/matches_reduce_branches.rs:35:2: 35:2
StorageDead(_6); // scope 4 at $DIR/matches_reduce_branches.rs:33:6: 33:7
StorageLive(_7); // scope 4 at $DIR/matches_reduce_branches.rs:35:6: 35:7
_7 = _2; // scope 4 at $DIR/matches_reduce_branches.rs:35:6: 35:7
StorageLive(_8); // scope 4 at $DIR/matches_reduce_branches.rs:35:9: 35:10
_8 = _3; // scope 4 at $DIR/matches_reduce_branches.rs:35:9: 35:10
StorageLive(_9); // scope 4 at $DIR/matches_reduce_branches.rs:35:12: 35:13
_9 = _4; // scope 4 at $DIR/matches_reduce_branches.rs:35:12: 35:13
StorageLive(_10); // scope 4 at $DIR/matches_reduce_branches.rs:35:15: 35:16
_10 = _5; // scope 4 at $DIR/matches_reduce_branches.rs:35:15: 35:16
(_0.0: bool) = move _7; // scope 4 at $DIR/matches_reduce_branches.rs:35:5: 35:17
(_0.1: bool) = move _8; // scope 4 at $DIR/matches_reduce_branches.rs:35:5: 35:17
(_0.2: bool) = move _9; // scope 4 at $DIR/matches_reduce_branches.rs:35:5: 35:17
(_0.3: bool) = move _10; // scope 4 at $DIR/matches_reduce_branches.rs:35:5: 35:17
StorageDead(_10); // scope 4 at $DIR/matches_reduce_branches.rs:35:16: 35:17
StorageDead(_9); // scope 4 at $DIR/matches_reduce_branches.rs:35:16: 35:17
StorageDead(_8); // scope 4 at $DIR/matches_reduce_branches.rs:35:16: 35:17
StorageDead(_7); // scope 4 at $DIR/matches_reduce_branches.rs:35:16: 35:17
StorageDead(_5); // scope 3 at $DIR/matches_reduce_branches.rs:36:1: 36:2
StorageDead(_4); // scope 2 at $DIR/matches_reduce_branches.rs:36:1: 36:2
StorageDead(_3); // scope 1 at $DIR/matches_reduce_branches.rs:36:1: 36:2
StorageDead(_2); // scope 0 at $DIR/matches_reduce_branches.rs:36:1: 36:2
return; // scope 0 at $DIR/matches_reduce_branches.rs:36:2: 36:2
}
}

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