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Auto merge of #93387 - JakobDegen:improve_partialeq, r=tmiasko
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)
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38 changes: 38 additions & 0 deletions
38
...t/uninhabited_fallthrough_elimination.eliminate_fallthrough.UninhabitedEnumBranching.diff
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,38 @@ | ||
| - // MIR for `eliminate_fallthrough` before UninhabitedEnumBranching | ||
| + // MIR for `eliminate_fallthrough` after UninhabitedEnumBranching | ||
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| 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 | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
| } | ||
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34 changes: 34 additions & 0 deletions
34
...ir-opt/uninhabited_fallthrough_elimination.keep_fallthrough.UninhabitedEnumBranching.diff
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,34 @@ | ||
| - // MIR for `keep_fallthrough` before UninhabitedEnumBranching | ||
| + // MIR for `keep_fallthrough` after UninhabitedEnumBranching | ||
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| 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 | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| 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 | ||
| } | ||
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| bb4: { | ||
| return; // scope 0 at $DIR/uninhabited_fallthrough_elimination.rs:18:2: 18:2 | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| enum Empty {} | ||
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| enum S { | ||
| A(Empty), | ||
| B, | ||
| C, | ||
| } | ||
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| use S::*; | ||
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| // EMIT_MIR uninhabited_fallthrough_elimination.keep_fallthrough.UninhabitedEnumBranching.diff | ||
| fn keep_fallthrough(s: S) -> u32 { | ||
| match s { | ||
| A(_) => 1, | ||
| B => 2, | ||
| _ => 3, | ||
| } | ||
| } | ||
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| // EMIT_MIR uninhabited_fallthrough_elimination.eliminate_fallthrough.UninhabitedEnumBranching.diff | ||
| fn eliminate_fallthrough(s: S) -> u32 { | ||
| match s { | ||
| C => 1, | ||
| B => 2, | ||
| _ => 3, | ||
| } | ||
| } | ||
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| fn main() { | ||
| keep_fallthrough(B); | ||
| eliminate_fallthrough(B); | ||
| } |