df984edf44
Do not lifetime-extend array/slice indices When lowering non-overloaded indexing operations to MIR, this uses the temporary lifetime of the index expression for the index temporary, rather than applying the temporary lifetime of the indexing operation as a whole to the index. For example, in ```rust let x = &xs[i]; ``` previously, the temporary containing the result of evaluating `i` would live until the end of the block due to the indexing operation being [lifetime-extended](https://doc.rust-lang.org/nightly/reference/destructors.html#temporary-lifetime-extension). Under this PR, the index temporary only lives to the end of the `let` statement because it uses the more precise temporary lifetime of the index expression. I don't think this will affect semantics in an observable way, but the more precise `StorageDead` placement may slightly improve analysis/codegen performance. r? mir
60 lines
1.6 KiB
Diff
60 lines
1.6 KiB
Diff
- // MIR for `dereference_indexing` before GVN
|
|
+ // MIR for `dereference_indexing` after GVN
|
|
|
|
fn dereference_indexing(_1: [u8; 2], _2: usize) -> () {
|
|
debug array => _1;
|
|
debug index => _2;
|
|
let mut _0: ();
|
|
let _3: &u8;
|
|
let _4: usize;
|
|
let mut _5: usize;
|
|
let _6: usize;
|
|
let mut _7: bool;
|
|
let _8: ();
|
|
let mut _9: u8;
|
|
scope 1 {
|
|
debug a => _3;
|
|
}
|
|
scope 2 {
|
|
debug i => _4;
|
|
}
|
|
|
|
bb0: {
|
|
StorageLive(_3);
|
|
- StorageLive(_4);
|
|
+ nop;
|
|
StorageLive(_5);
|
|
_5 = copy _2;
|
|
- _4 = Add(move _5, const 1_usize);
|
|
+ _4 = Add(copy _2, const 1_usize);
|
|
StorageDead(_5);
|
|
StorageLive(_6);
|
|
_6 = copy _4;
|
|
- _7 = Lt(copy _6, const 2_usize);
|
|
- assert(move _7, "index out of bounds: the length is {} but the index is {}", const 2_usize, copy _6) -> [success: bb1, unwind unreachable];
|
|
+ _7 = Lt(copy _4, const 2_usize);
|
|
+ assert(move _7, "index out of bounds: the length is {} but the index is {}", const 2_usize, copy _4) -> [success: bb1, unwind unreachable];
|
|
}
|
|
|
|
bb1: {
|
|
- _3 = &_1[_6];
|
|
- StorageDead(_4);
|
|
+ _3 = &_1[_4];
|
|
+ nop;
|
|
StorageDead(_6);
|
|
StorageLive(_8);
|
|
StorageLive(_9);
|
|
- _9 = copy (*_3);
|
|
+ _9 = copy _1[_4];
|
|
_8 = opaque::<u8>(move _9) -> [return: bb2, unwind unreachable];
|
|
}
|
|
|
|
bb2: {
|
|
StorageDead(_9);
|
|
StorageDead(_8);
|
|
_0 = const ();
|
|
StorageDead(_3);
|
|
return;
|
|
}
|
|
}
|
|
|