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Rollup merge of #100239 - RalfJung:const-prop-uninit, r=oli-obk

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remove an ineffective check in const_prop

Based on https://github.com/rust-lang/rust/pull/100043, only the last two commits are new.

ConstProp has a special check when reading from a local that prevents reading uninit locals. However, if that local flows into `force_allocation`, then no check fires and evaluation proceeds. So this check is not really effective at preventing accesses to uninit locals.

With https://github.com/rust-lang/rust/pull/100043, `read_immediate` and friends always fail when reading uninit locals, so I don't see why ConstProp would need a separate check. Thus I propose we remove it. This is needed to be able to do https://github.com/rust-lang/rust/pull/100085.
This commit is contained in:
Dylan DPC 2022-08-29 16:49:40 +05:30 • committed by GitHub
commit 3ea5456366
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8 changed files with 64 additions and 58 deletions
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src/test/mir-opt/const_prop/mutable_variable_unprop_assign.main.ConstProp.diff
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@ -41,7 +41,8 @@
StorageLive(_4); // scope 2 at $DIR/mutable_variable_unprop_assign.rs:+4:9: +4:10
_4 = (_2.1: i32); // scope 2 at $DIR/mutable_variable_unprop_assign.rs:+4:13: +4:16
StorageLive(_5); // scope 3 at $DIR/mutable_variable_unprop_assign.rs:+5:9: +5:10
_5 = (_2.0: i32); // scope 3 at $DIR/mutable_variable_unprop_assign.rs:+5:13: +5:16
- _5 = (_2.0: i32); // scope 3 at $DIR/mutable_variable_unprop_assign.rs:+5:13: +5:16
+ _5 = const 1_i32; // scope 3 at $DIR/mutable_variable_unprop_assign.rs:+5:13: +5:16
nop; // scope 0 at $DIR/mutable_variable_unprop_assign.rs:+0:11: +6:2
StorageDead(_5); // scope 3 at $DIR/mutable_variable_unprop_assign.rs:+6:1: +6:2
StorageDead(_4); // scope 2 at $DIR/mutable_variable_unprop_assign.rs:+6:1: +6:2