fixes move analysis #49392

hrvolapeter · 2018-03-26T20:11:26Z

Fixed compiler error by correct checking when dereferencing

@nikomatsakis

librustc_mir/transform/elaborate_drops.rs — drop of untracked, uninitialized value Fix #48962 r? @nikomatsakis

rust-highfive · 2018-03-26T20:11:39Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

shepmaster · 2018-03-30T19:38:02Z

Ping from triage, @nikomatsakis ! Will you have time to review this soon?

arielb1 · 2018-03-31T21:56:12Z

src/librustc_mir/borrow_check/mod.rs

@@ -1454,8 +1492,6 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                Place::Projection(ref proj) => {
                    let Projection { ref base, ref elem } = **proj;
                    match *elem {
-                        ProjectionElem::Deref |
-                        // assigning to *P requires `P` initialized.
                        ProjectionElem::Index(_/*operand*/) |
                        ProjectionElem::ConstantIndex { .. } |
                        // assigning to P[i] requires `P` initialized.


This comment is wrong. Should be

// assigning to P[i] requires P to be valid

arielb1 · 2018-03-31T21:56:31Z

src/librustc_mir/borrow_check/mod.rs

@@ -1465,6 +1501,12 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                        // FIXME: is this true even if P is a adt with a dtor?
                        { }

+                        ProjectionElem::Deref => {


Should have a comment

// assigning to (*P) requires P to be initialized

arielb1 · 2018-03-31T21:57:22Z

src/librustc_mir/borrow_check/mod.rs

+                        ProjectionElem::Deref => {
+                            self.check_if_path_is_moved(
+                                context, InitializationRequiringAction::Use,
+                                (base, span), flow_state);


You can add a break here if you want - we already force the base to be initialized, so there is no need to further check.

Maybe in that case you would also not need the new error deduplication code.

arielb1 · 2018-03-31T22:02:14Z

src/librustc_mir/borrow_check/mod.rs

@@ -1320,18 +1324,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
        //


Maybe rename check_if_path_is_moved to check_if_full_path_is_moved?

arielb1 · 2018-03-31T22:03:33Z

Sorry for the delay in reviewing. This is a bit of an embarrassing bug.

If adding a break in the check_if_assigned_path_is_moved loop fixes the error duplication, then pretty much r+ from me with the nits addressed.

hrvolapeter · 2018-04-01T08:10:56Z

@arielb1 Unfortunately adding a break won't fix duplicate errors. Let's have expression w[5] = 0; it translates to mir similar to

        _3 = Len((*_1));                 // bb0[3]: scope 1 at borrowck-use-in-index-lvalue.rs:16:5: 16:9
                                         | Live variables on entry to bb0[4]: [_1, _2, _3]
        _4 = Lt(_2, _3);                 // bb0[4]: scope 1 at borrowck-use-in-index-lvalue.rs:16:5: 16:9
                                         | Live variables on entry to bb0[5]: [_1, _2, _3, _4]
        assert(move _4, "index out of bounds: the len is {} but the index is {}", move _3, _2) -> [success: bb2, unwind: bb1]; // bb0[5]: scope 1 at borrowck-use-in-index-lvalue.rs:16:5: 16:9
    }

    | Live variables on entry to bb1: []
    bb1: {                               // cleanup
                                         | Live variables on entry to bb1[0]: []
        resume;                          // bb1[0]: scope 0 at borrowck-use-in-index-lvalue.rs:14:1: 22:2
    }

    | Live variables on entry to bb2: [_1, _2]
    bb2: {                              
                                         | Live variables on entry to bb2[0]: [_1, _2]
        (*_1)[_2] = const 0isize;

the first error is printed from _3 = Len((*_1)); and the second (which we are trying to surpress) is from (*_1)[_2] = const 0isize;
We did not have second error till now due to incorrect deref checkin.

arielb1 · 2018-04-01T21:24:27Z

@retep007

In that case, could you deduplicate based on (Place, Span) instead of only Place? That makes e.g. writing tests to much easier.

arielb1 · 2018-04-01T21:25:17Z

src/librustc_mir/borrow_check/error_reporting.rs

+                .contains(&root_place.clone())
+            {
+                debug!(
+                    "report_use_of_moved_or_uninitialized place: {:?} errors was suppressed",


english fix: error about {:?} suppressed.

arielb1 · 2018-04-01T21:26:08Z

I think this code is OK, but I didn't touch this code long enough that I would rather

r? @nikomatsakis

hrvolapeter · 2018-04-02T07:09:38Z

@arielb1 _3 = Len((*_1)); and (*_1)[_2] = const 0isize; have also different spans from previous comment first one has span only of w[5] but second has w[5] = 0.

I also think that second error actually says better what's the problem, but It would require to first refactor how the errors are reported.
First:

w[5] = 0; //[ast]~ ERROR use of possibly uninitialized variable: `w` [E0381]
^^^^ use of possibly uninitialized `*w`

Second:

w[5] = 0; //[ast]~ ERROR use of possibly uninitialized variable: `w` [E0381]
^^^^^^^^ use of possibly uninitialized `w`

nikomatsakis · 2018-04-02T20:43:54Z

src/librustc_mir/borrow_check/mod.rs

+        place_span: (&Place<'tcx>, Span),
+        flow_state: &Flows<'cx, 'gcx, 'tcx>,
+    ) {
+        // FIXME: analogous code in check_loans first maps `place` to


what code are you referring to exactly?

Exactly same code let place = self.base_path(place_span.0); is in check_if_full_path_is_moved also with the comment. So If somebody decides to refactor this he will probably do both check_if_full_path_is_moved, check_if_path_or_subpath_is_moved

nikomatsakis · 2018-04-02T20:52:33Z

This code looks good to me!

hrvolapeter · 2018-04-03T09:15:55Z

@bors r=nikomatsakis

bors · 2018-04-03T09:15:56Z

@retep007: 🔑 Insufficient privileges: Not in reviewers

hrvolapeter · 2018-04-03T09:16:40Z

@nikomatsakis Could you also accept it by bors?

pnkfelix · 2018-04-03T14:40:52Z

@bors r=nikomatsakis

bors · 2018-04-03T14:40:53Z

📌 Commit 9056c7a has been approved by nikomatsakis

kennytm · 2018-04-06T19:58:08Z

@bors p=6

bors · 2018-04-06T21:50:21Z

⌛ Testing commit 9056c7a with merge 0e35ddd...

@nikomatsakis

fixes move analysis Fixed compiler error by correct checking when dereferencing Fix #48962 r? @nikomatsakis

bors · 2018-04-07T00:20:15Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 0e35ddd to master...

fixes internal compiler error:

4954e3e

librustc_mir/transform/elaborate_drops.rs — drop of untracked, uninitialized value Fix #48962 r? @nikomatsakis

rust-highfive assigned nikomatsakis Mar 26, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 26, 2018

arielb1 reviewed Mar 31, 2018

View reviewed changes

Fixed nits from PR review #49392

dc41851

arielb1 reviewed Apr 1, 2018

View reviewed changes

Fixed error message from PR review #49392

9056c7a

nikomatsakis approved these changes Apr 2, 2018

View reviewed changes

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 3, 2018

alexcrichton mentioned this pull request Apr 5, 2018

Rollup of 11 pull requests #49675

Closed

alexcrichton mentioned this pull request Apr 5, 2018

Rollup of 8 pull requests #49696

Merged

bors added a commit that referenced this pull request Apr 6, 2018

Auto merge of #49392 - retep007:nll-issue-48962, r=nikomatsakis

0e35ddd

fixes move analysis Fixed compiler error by correct checking when dereferencing Fix #48962 r? @nikomatsakis

bors merged commit 9056c7a into rust-lang:master Apr 7, 2018

bors mentioned this pull request Apr 7, 2018

Allow MIR borrowck to catch unused mutable locals #48605

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fixes move analysis #49392

fixes move analysis #49392

hrvolapeter commented Mar 26, 2018

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shepmaster commented Mar 30, 2018

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bors commented Apr 6, 2018

bors commented Apr 7, 2018

		@@ -1320,18 +1324,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
		//

fixes move analysis #49392

fixes move analysis #49392

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