[WIP] Take 2: change how MIR represents Place

[csmoe]

Closes #52708
Introduce the new Place with "incremental refactoring" instead of the previous approach which is hard to maintain.
r? @nikomatsakis

[eddyb]

I find this operation dishearteningly inefficient :(.

[nikomatsakis]

If we don't "re-intern" the slice of elements, then in what way is it inefficient?

I think it'd be nice to be able to treat a NeoPlace as either a list or a tree as you choose, and this operation allows for that (although I would probably tweak the signature; I'd prefer it returns something like "Result<(NeoPlace, ProjectionElem), Base>`. ie., either you reached the base case, or else not.

[nikomatsakis]

Maybe something like

enum NeoPlaceTree {
    Leaf(PlaceBase),
    Branch(NeoPlace<'tcx>, ProjectionElem<'tcx>),
}

and into_tree(self) -> NeoPlaceTree as the signature (lifetimes elided, clearly).

[eddyb]

You can rewrite this as going backwards in the projection list.

If you want, you can use let mut elems = self.elems.iter().rev(); and then call next() on that once, check whether it's Deref, and if it is, call next() again.

You can also use indices.

[nikomatsakis]

It feels like this is a case where treating the projection as a tree (sort of what this code is doing) is a bit cleaner. In particular, we want to look for something like P.f or *P.f and then test the type of P. We can certainly "walk backwards" over the elements, but once we've peeled off the * and the .f we sitll kind of want to extract the P as a unit, right?

[nikomatsakis]

There is no need to intern again here; just use place_elems directly. It is already pointing into interned memory, right?

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The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:284e2dda:start=1549091148431928579,finish=1549091220787576161,duration=72355647582
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:24:46]    Compiling rustc_lsan v0.0.0 (/checkout/src/librustc_lsan)
[00:24:46]    Compiling rustc_asan v0.0.0 (/checkout/src/librustc_asan)
[00:24:46]    Compiling rustc_msan v0.0.0 (/checkout/src/librustc_msan)
[00:24:47]    Compiling rustc_tsan v0.0.0 (/checkout/src/librustc_tsan)
[00:25:03] error: internal compiler error: src/librustc_mir/borrow_check/nll/mod.rs:355: region is not an ReVar: ReFree(DefId(0/0:432 ~ core[255e]::num[0]::dec2flt[0]::simplify[0]), BrAnon(1))
[00:25:03] thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:605:9
[00:25:03] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:25:03] error: aborting due to previous error
[00:25:03] 
[00:25:03] 
[00:25:03] 
[00:25:03] note: the compiler unexpectedly panicked. this is a bug.
[00:25:03] 
[00:25:03] note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
[00:25:03] 
[00:25:03] note: rustc 1.34.0-dev running on x86_64-unknown-linux-gnu
[00:25:03] 
[00:25:03] note: compiler flags: -Z force-unstable-if-unmarked -C opt-level=2 -C prefer-dynamic -C debug-assertions=y -C codegen-units=1 -C link-args=-Wl,-rpath,$ORIGIN/../lib --crate-type lib
[00:25:03] note: some of the compiler flags provided by cargo are hidden
[00:25:03] 
[00:25:03] error: Could not compile `core`.
[00:25:03] 
[00:25:03] 
[00:25:03] To learn more, run the command again with --verbose.
[00:25:03] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:25:03] expected success, got: exit code: 101
[00:25:03] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:25:03] Build completed unsuccessfully in 0:21:14
[00:25:03] make: *** [all] Error 1
[00:25:03] Makefile:18: recipe for target 'all' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0082e6c6
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sat Feb  2 07:32:13 UTC 2019
---
travis_time:end:15f08311:start=1549092733938533154,finish=1549092733944846785,duration=6313631
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:1bd8ce04
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
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travis_time:start:0ef9f73c
travis_time:start:0ef9f73c
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:09bd5980
$ dmesg | grep -i kill

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 @TimNN. (Feature Requests)

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The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:31276a3e:start=1549133827288055381,finish=1549133899272265488,duration=71984210107
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---

[00:03:44] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:44] tidy error: /checkout/src/librustc_mir/borrow_check/borrow_set.rs:214: line longer than 100 chars
[00:03:44] tidy error: /checkout/src/librustc_mir/transform/uniform_array_move_out.rs:79: line longer than 100 chars
[00:03:45] tidy error: /checkout/src/librustc/mir/visit.rs:787: trailing whitespace
[00:03:45] tidy error: /checkout/src/librustc/mir/visit.rs:789: trailing whitespace
[00:03:46] some tidy checks failed
[00:03:46] 
[00:03:46] 
[00:03:46] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:46] 
[00:03:46] 
[00:03:46] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:46] Build completed unsuccessfully in 0:00:44
[00:03:46] Build completed unsuccessfully in 0:00:44
[00:03:46] make: *** [tidy] Error 1
[00:03:46] Makefile:68: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:2d8267e8
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sat Feb  2 19:02:15 UTC 2019
---
travis_time:end:02a99815:start=1549134136249362228,finish=1549134136254003684,duration=4641456
travis_fold:end:after_failure.3
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travis_time:start:04c93a40
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:09afa808
travis_time:start:09afa808
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:0a2a077c
$ dmesg | grep -i kill

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 @TimNN. (Feature Requests)

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:1f5684c6:start=1549154738184715049,finish=1549154813556430569,duration=75371715520
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---

[00:03:20] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:20] tidy error: /checkout/src/librustc_mir/borrow_check/borrow_set.rs:214: line longer than 100 chars
[00:03:20] tidy error: /checkout/src/librustc_mir/transform/uniform_array_move_out.rs:79: line longer than 100 chars
[00:03:20] tidy error: /checkout/src/librustc/mir/visit.rs:774: trailing whitespace
[00:03:20] tidy error: /checkout/src/librustc/mir/visit.rs:776: trailing whitespace
[00:03:22] some tidy checks failed
[00:03:22] 
[00:03:22] 
[00:03:22] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:22] 
[00:03:22] 
[00:03:22] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:22] Build completed unsuccessfully in 0:00:48
[00:03:22] Build completed unsuccessfully in 0:00:48
[00:03:22] make: *** [tidy] Error 1
[00:03:22] Makefile:68: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:2ddd6ca7
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sun Feb  3 00:50:24 UTC 2019
---
travis_time:end:1cb84358:start=1549155025432858411,finish=1549155025437535335,duration=4676924
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:2fef8338
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0c00ada0
travis_time:start:0c00ada0
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:03ea0bac
$ dmesg | grep -i kill

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The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:23838cd8:start=1549198197086786975,finish=1549198275119672570,duration=78032885595
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
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Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---

[00:03:12] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:12] tidy error: /checkout/src/librustc_mir/borrow_check/borrow_set.rs:214: line longer than 100 chars
[00:03:12] tidy error: /checkout/src/librustc_mir/transform/uniform_array_move_out.rs:79: line longer than 100 chars
[00:03:13] tidy error: /checkout/src/librustc/mir/visit.rs:774: trailing whitespace
[00:03:13] tidy error: /checkout/src/librustc/mir/visit.rs:776: trailing whitespace
[00:03:14] some tidy checks failed
[00:03:14] 
[00:03:14] 
[00:03:14] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:14] 
[00:03:14] 
[00:03:14] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:14] Build completed unsuccessfully in 0:00:46
[00:03:14] Build completed unsuccessfully in 0:00:46
[00:03:14] make: *** [tidy] Error 1
[00:03:14] Makefile:68: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0070f1eb
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sun Feb  3 12:54:38 UTC 2019
---
travis_time:end:00a64d60:start=1549198479481187588,finish=1549198479486293567,duration=5105979
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travis_time:start:00c818df
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
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travis_time:start:00ad4ffd
travis_time:start:00ad4ffd
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:26842de1
$ dmesg | grep -i kill

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[bors]

☔ The latest upstream changes (presumably #58254) made this pull request unmergeable. Please resolve the merge conflicts.

[spastorino]

After conversations about MIR 2.0, I think this PR doesn't make sense anymore as is. In any case this is being discussed in Zulip.