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Auto merge of #56764 - sinkuu:simpcfg_bb0, r=matthewjasper

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mir-opt: Make SimplifyCfg collapse goto chains starting from bb0

`SimplifyCfg` pass was not able to collapse goto chains starting from bb0, leaving MIR like this:

```
bb0: {
    goto -> bb1;
}
```
This commit is contained in:
bors 2018-12-17 06:34:04 +00:00
commit 7fb479c92b
2 changed files with 80 additions and 1 deletions
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54
src/test/mir-opt/simplify_cfg.rs Normal file
View file

@ -0,0 +1,54 @@
// Test that the goto chain starting from bb0 is collapsed.
fn main() {
loop {
if bar() {
break;
}
}
}
#[inline(never)]
fn bar() -> bool {
true
}
// END RUST SOURCE
// START rustc.main.SimplifyCfg-initial.before.mir
// bb0: {
// goto -> bb1;
// }
// bb1: {
// falseUnwind -> [real: bb3, cleanup: bb4];
// }
// ...
// bb11: {
// ...
// goto -> bb1;
// }
// END rustc.main.SimplifyCfg-initial.before.mir
// START rustc.main.SimplifyCfg-initial.after.mir
// bb0: {
// falseUnwind -> [real: bb1, cleanup: bb2];
// }
// ...
// bb5: {
// ...
// goto -> bb0;
// }
// END rustc.main.SimplifyCfg-initial.after.mir
// START rustc.main.SimplifyCfg-early-opt.before.mir
// bb0: {
// goto -> bb1;
// }
// bb1: {
// StorageLive(_2);
// _2 = const bar() -> bb3;
// }
// END rustc.main.SimplifyCfg-early-opt.before.mir
// START rustc.main.SimplifyCfg-early-opt.after.mir
// bb0: {
// StorageLive(_2);
// _2 = const bar() -> bb1;
// }
// END rustc.main.SimplifyCfg-early-opt.after.mir