015a824f2d
UnreachableProp: Preserve unreachable branches for multiple targets
Before, UnreachablePropagation removed all unreachable branches. This was a pessimization, as it removed information about reachability that was used later in the optimization pipeline.
For example, this code
```rust
pub enum Two { A, B }
pub fn identity(x: Two) -> Two {
match x {
Two::A => Two::A,
Two::B => Two::B,
}
}
```
basically has `switchInt() -> [0: 0, 1: 1, otherwise: unreachable]` for the match. This allows it to be transformed into a simple `x`. If we remove the unreachable branch, the transformation becomes illegal.
This was the problem keeping `UnreachablePropagation` from being enabled, so we can enable it now.
Something similar already happened in #77800, but it did not show a perf improvement there. Let's try it again anyways!
Fixes #68105, although that issue has been fixed for a long time (see #77680).
83 lines
5.4 KiB
Rust
83 lines
5.4 KiB
Rust
// MIR for `try_identity` after SimplifyBranchSame
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fn try_identity(_1: Result<u32, i32>) -> Result<u32, i32> {
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debug x => _1; // in scope 0 at $DIR/simplify_try.rs:+0:17: +0:18
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let mut _0: std::result::Result<u32, i32>; // return place in scope 0 at $DIR/simplify_try.rs:+0:41: +0:57
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let _2: u32; // in scope 0 at $DIR/simplify_try.rs:+1:9: +1:10
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let mut _3: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:+1:19: +1:33
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let mut _4: std::result::Result<u32, i32>; // in scope 0 at $DIR/simplify_try.rs:+1:31: +1:32
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let mut _5: isize; // in scope 0 at $DIR/simplify_try.rs:+2:9: +2:15
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let _6: i32; // in scope 0 at $DIR/simplify_try.rs:+2:13: +2:14
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let mut _7: !; // in scope 0 at $DIR/simplify_try.rs:+2:19: +2:51
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let mut _8: i32; // in scope 0 at $DIR/simplify_try.rs:+2:37: +2:50
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let mut _9: i32; // in scope 0 at $DIR/simplify_try.rs:+2:48: +2:49
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let _10: u32; // in scope 0 at $DIR/simplify_try.rs:+3:12: +3:13
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let mut _11: u32; // in scope 0 at $DIR/simplify_try.rs:+5:8: +5:9
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scope 1 {
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debug y => _2; // in scope 1 at $DIR/simplify_try.rs:+1:9: +1:10
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}
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scope 2 {
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debug e => _6; // in scope 2 at $DIR/simplify_try.rs:+2:13: +2:14
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scope 5 (inlined <i32 as From<i32>>::from) { // at $DIR/simplify_try.rs:22:37: 22:50
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debug t => _9; // in scope 5 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
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}
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scope 6 (inlined from_error::<u32, i32>) { // at $DIR/simplify_try.rs:22:26: 22:51
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debug e => _8; // in scope 6 at $DIR/simplify_try.rs:12:21: 12:22
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}
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}
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scope 3 {
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debug v => _10; // in scope 3 at $DIR/simplify_try.rs:+3:12: +3:13
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}
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scope 4 (inlined into_result::<u32, i32>) { // at $DIR/simplify_try.rs:21:19: 21:33
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debug r => _4; // in scope 4 at $DIR/simplify_try.rs:8:22: 8:23
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}
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bb0: {
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StorageLive(_2); // scope 0 at $DIR/simplify_try.rs:+1:9: +1:10
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StorageLive(_3); // scope 0 at $DIR/simplify_try.rs:+1:19: +1:33
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StorageLive(_4); // scope 0 at $DIR/simplify_try.rs:+1:31: +1:32
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_4 = _1; // scope 0 at $DIR/simplify_try.rs:+1:31: +1:32
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_3 = move _4; // scope 4 at $DIR/simplify_try.rs:9:5: 9:6
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StorageDead(_4); // scope 0 at $DIR/simplify_try.rs:+1:32: +1:33
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_5 = discriminant(_3); // scope 0 at $DIR/simplify_try.rs:+1:19: +1:33
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switchInt(move _5) -> [0_isize: bb1, 1_isize: bb3, otherwise: bb2]; // scope 0 at $DIR/simplify_try.rs:+1:13: +1:33
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}
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bb1: {
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StorageLive(_10); // scope 0 at $DIR/simplify_try.rs:+3:12: +3:13
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_10 = ((_3 as Ok).0: u32); // scope 0 at $DIR/simplify_try.rs:+3:12: +3:13
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_2 = _10; // scope 3 at $DIR/simplify_try.rs:+3:18: +3:19
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StorageDead(_10); // scope 0 at $DIR/simplify_try.rs:+3:18: +3:19
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StorageDead(_3); // scope 0 at $DIR/simplify_try.rs:+4:6: +4:7
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StorageLive(_11); // scope 1 at $DIR/simplify_try.rs:+5:8: +5:9
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_11 = _2; // scope 1 at $DIR/simplify_try.rs:+5:8: +5:9
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Deinit(_0); // scope 1 at $DIR/simplify_try.rs:+5:5: +5:10
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((_0 as Ok).0: u32) = move _11; // scope 1 at $DIR/simplify_try.rs:+5:5: +5:10
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discriminant(_0) = 0; // scope 1 at $DIR/simplify_try.rs:+5:5: +5:10
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StorageDead(_11); // scope 1 at $DIR/simplify_try.rs:+5:9: +5:10
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StorageDead(_2); // scope 0 at $DIR/simplify_try.rs:+6:1: +6:2
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return; // scope 0 at $DIR/simplify_try.rs:+6:2: +6:2
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}
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bb2: {
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unreachable; // scope 0 at $DIR/simplify_try.rs:+1:19: +1:33
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}
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bb3: {
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StorageLive(_6); // scope 0 at $DIR/simplify_try.rs:+2:13: +2:14
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_6 = ((_3 as Err).0: i32); // scope 0 at $DIR/simplify_try.rs:+2:13: +2:14
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StorageLive(_8); // scope 2 at $DIR/simplify_try.rs:+2:37: +2:50
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StorageLive(_9); // scope 2 at $DIR/simplify_try.rs:+2:48: +2:49
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_9 = _6; // scope 2 at $DIR/simplify_try.rs:+2:48: +2:49
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_8 = move _9; // scope 5 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
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StorageDead(_9); // scope 2 at $DIR/simplify_try.rs:+2:49: +2:50
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((_0 as Err).0: i32) = move _8; // scope 6 at $DIR/simplify_try.rs:13:9: 13:10
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Deinit(_0); // scope 6 at $DIR/simplify_try.rs:13:5: 13:11
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discriminant(_0) = 1; // scope 6 at $DIR/simplify_try.rs:13:5: 13:11
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StorageDead(_8); // scope 2 at $DIR/simplify_try.rs:+2:50: +2:51
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StorageDead(_6); // scope 0 at $DIR/simplify_try.rs:+2:50: +2:51
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StorageDead(_3); // scope 0 at $DIR/simplify_try.rs:+4:6: +4:7
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StorageDead(_2); // scope 0 at $DIR/simplify_try.rs:+6:1: +6:2
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return; // scope 0 at $DIR/simplify_try.rs:+6:2: +6:2
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}
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}
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