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NLL: Suggest extraction of subcomputation into a new binding - #53305
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KiChjang wants to merge 1 commit into
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NLL: Suggest extraction of subcomputation into a new binding#53305KiChjang wants to merge 1 commit into
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KiChjang
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Aug 13, 2018
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I wonder if there's an issue filed for this diagnostic change? It looks to be a worse version of what we have in the AST borrowck.
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Are you referring to the "really big span"?
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I'm not sure if there is an issue but I agree it's a diagnostic regression
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The complete MIR for the Details// MIR for `foo`// source = MirSource { def_id: DefId(0/0:9 ~ borrowck_suggest_extraction_of_subcomputation[317d]::foo[0]), promoted: None }// pass_name = SimplifyCfg-initial// disambiguator = afterfnfoo(_1:B) -> (){letmut _0:();// return placescope1{}
scope 2{let _2:u32;// "key" in scope 2 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:24:9: 24:12}letmut _3:&mut[u32];letmut _4:&mutB;letmut _5:usize;letmut _6:usize;letmut _7:usize;letmut _8:u32;letmut _9:usize;letmut _10:&B;letmut _11:usize;letmut _12:bool;bb0:{StorageLive(_2);// bb0[0]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:24:9: 24:12
_2 = const0u32;// bb0[1]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:24:15: 24:19// ty::Const// + ty: u32// + val: Scalar(Bits { size: 4, bits: 0 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:24:15: 24:19// + ty: u32// + literal: Const { ty: u32, val: Scalar(Bits { size: 4, bits: 0 }) }StorageLive(_3);// bb0[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:24StorageLive(_4);// bb0[3]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:12
_4 = &mut _1;// bb0[4]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:12
_3 = constSliceWrapperMut::slice_mut(move _4) -> [return: bb2, unwind: bb3];// bb0[5]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:24// ty::Const// + ty: for<'r> fn(&'r mut B) -> &'r mut [u32] {<B as SliceWrapperMut<u32>>::slice_mut}// + val: Scalar(Bits { size: 0, bits: 0 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:24// + ty: for<'r> fn(&'r mut B) -> &'r mut [u32] {<B as SliceWrapperMut<u32>>::slice_mut}// + literal: Const { ty: for<'r> fn(&'r mut B) -> &'r mut [u32] {<B as SliceWrapperMut<u32>>::slice_mut}, val: Scalar(Bits { size: 0, bits: 0 }) }}bb1:{// cleanup
resume;// bb1[0]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:23:1: 27:2}
bb2:{StorageDead(_4);// bb2[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:23: 25:24StorageLive(_5);// bb2[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:86StorageLive(_6);// bb2[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:56StorageLive(_7);// bb2[3]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:39StorageLive(_8);// bb2[4]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:26: 25:29
_8 = _2;// bb2[5]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:26: 25:29
_7 = move _8 asusize(Misc);// bb2[6]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:39StorageDead(_8);// bb2[7]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:38: 25:39
_6 = const core::num::<impl usize>::wrapping_add(move _7,const22usize) -> [return:bb4,unwind:bb3];// bb2[8]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:56// ty::Const// + ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_add}// + val: Scalar(Bits { size: 0, bits: 0 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:56// + ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_add}// + literal: Const { ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_add}, val: Scalar(Bits { size: 0, bits: 0 }) }// ty::Const// + ty: usize// + val: Scalar(Bits { size: 8, bits: 22 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:53: 25:55// + ty: usize// + literal: Const { ty: usize, val: Scalar(Bits { size: 8, bits: 22 }) }}
bb3:{// cleanupEndRegion();// bb3[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:87drop(_1) -> bb1;// bb3[1]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:27:1: 27:2}bb4:{StorageDead(_7);// bb4[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:55: 25:56StorageLive(_9);// bb4[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85StorageLive(_10);// bb4[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:77
_10 = &_1;// bb4[3]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:77
_9 = constSweep::sweep(move _10) -> [return: bb5, unwind: bb6];// bb4[4]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85// ty::Const// + ty: for<'r> fn(&'r B) -> usize {<B as Sweep>::sweep}// + val: Scalar(Bits { size: 0, bits: 0 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85// + ty: for<'r> fn(&'r B) -> usize {<B as Sweep>::sweep}// + literal: Const { ty: for<'r> fn(&'r B) -> usize {<B as Sweep>::sweep}, val: Scalar(Bits { size: 0, bits: 0 }) }}bb5:{EndRegion();// bb5[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85StorageDead(_10);// bb5[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:84: 25:85
_5 = const core::num::<impl usize>::wrapping_rem(move _6,move _9) -> [return:bb7,unwind:bb3];// bb5[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:86// ty::Const// + ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_rem}// + val: Scalar(Bits { size: 0, bits: 0 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:25: 25:86// + ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_rem}// + literal: Const { ty: fn(usize, usize) -> usize {core::num::<impl usize>::wrapping_rem}, val: Scalar(Bits { size: 0, bits: 0 }) }}bb6:{// cleanupEndRegion();// bb6[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85
goto -> bb3;// bb6[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:70: 25:85}bb7:{StorageDead(_9);// bb7[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:85: 25:86StorageDead(_6);// bb7[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:85: 25:86
_11 = Len((*_3));// bb7[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:87
_12 = Lt(_5, _11);// bb7[3]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:87assert(move _12,"index out of bounds: the len is move _11 but the index is _5") -> [success: bb8, unwind: bb3];// bb7[4]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:87}bb8:{EndRegion();// bb8[0]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:87(*_3)[_5] = const22u32;// bb8[1]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:5: 25:92// ty::Const// + ty: u32// + val: Scalar(Bits { size: 4, bits: 22 })// mir::Constant// + span: .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:90: 25:92// + ty: u32// + literal: Const { ty: u32, val: Scalar(Bits { size: 4, bits: 22 }) }StorageDead(_3);// bb8[2]: scope 1 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:25:92: 25:93
_0 = ();// bb8[3]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:23:77: 27:2StorageDead(_2);// bb8[4]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:27:1: 27:2drop(_1) -> [return: bb9, unwind: bb1];// bb8[5]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:27:1: 27:2}bb9:{ return;// bb9[0]: scope 0 at .\src\test\ui\borrowck\borrowck-suggest-extraction-of-subcomputation.rs:27:2: 27:2}} |
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rust-highfive
commented
Aug 13, 2018
Contributor
The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
KiChjang
commented
Aug 13, 2018
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One of the failed tests is quite interesting: It does feel like this PR is making the right recommendation for this test, but the rest of the failed test cases indicate that the current check requires more refinement. |
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@nikomatsakis To explain more what I was suggesting in Zulip, consider the MIR I've posted above: In bb0[4], we have an assignment of a mutable reference of _1 to _4, which then immediately gets used as an argument to a function in the next statement, the return value of which is stored in _3. Since there is no other statement between the assignment and the use of _4, there would not be a chance to run the analysis at all. I think a more correct formulation of the rule would be to check when _1 starts being borrowed and when its StorageDead statement is emitted. |
nikomatsakis
commented
Aug 22, 2018
Contributor
I'm a bit confused by your comment.
I'm not sure what you mean here -- run which analysis? Ah, I guess you are referring to these conditions that I wrote earlier:
I agree that what I wrote here doesn't seem exactly correct. When I wrote 'the call', of course, I was referring not to the call to One challenge is that this suggestion is sort of a "tree-based" one -- we basically want to see whether we could re-order some subcomputation (like Specifically I was looking for the case where you have I don't really think that looking for |
nikomatsakis
commented
Aug 22, 2018
Contributor
Sorry, that comment isn't really a "conclusion" -- more just me musing to myself. =) I have to run now though, will try to think a bit more in a bit. |
nikomatsakis
commented
Aug 22, 2018
Contributor
Let me know though if what I wrote makes sense and is 'aligned' with how you are thinking about the problem. =) |
nikomatsakis
commented
Aug 24, 2018
Contributor
@KiChjang so what do you think? After our discussion on Zulip I'm feeling a bit uncertain how to proceed here. |
KiChjang
commented
Aug 24, 2018
ContributorAuthor
@nikomatsakis Same here unfortunately, there doesn't seem to be a clear path forward, except for the "availability" analysis you mentioned, which is much more involved than what this PR is and I think that one is worth specc'ing out first. I have a feeling that anything else we do currently would be an inaccurate approximation of what the desired behavior is. |
nikomatsakis
commented
Aug 28, 2018
Contributor
OK, I guess we'll close this PR for now. We should raise the original issue for discussion today perhaps. |
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Fixes#47349.
r? @nikomatsakis