rustc_mir: allow promotion of promotable temps indexed at runtime.

[eddyb]

Fixes #49955.

r? @nikomatsakis

[rust-highfive]

The job x86_64-gnu-llvm-3.9 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.

Click to expand the log.

[00:52:10] ..................test [run-pass] run-pass/mir_heavy_promoted.rs has been running for over 60 seconds
[00:52:33] ..................................................................................
[00:52:52] ..................................................................................ii................
[00:53:42] ..............................................i....................................................i
[00:53:54] .ii.............................test [run-pass] run-pass/saturating-float-casts.rs has been running for over 60 seconds
[00:54:43] .......iiiiiii......................................................................................
[00:55:03] ....................................................................................................
[00:55:22] ....................................................................................................
[00:55:40] ................................................................................
---
travis_time:start:test_mir-opt
Check compiletest suite=mir-opt mode=mir-opt (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[00:58:57] 
[00:58:57] running 50 tests
[00:59:07] ERROR 2018-05-10T11:25:42Z: compiletest::runtest: Some(" bb9: { // binding1 and guard")
[00:59:18]      _9 = _4;
[00:59:18]      _9 = _4;
[00:59:18]      _1 = (const 1i32, move _9);
[00:59:18]      StorageDead(_9);
[00:59:18]      goto -> bb13;
[00:59:18]  }
[00:59:18]  bb3: { // binding3(empty) and arm3
[00:59:18]      _1 = (const 3i32, const 3i32);
[00:59:18]      goto -> bb13;
[00:59:18]  }
[00:59:18]  bb4: {
[00:59:18]      falseEdges -> [real: bb9, imaginary: bb5]; //pre_binding1
[00:59:18]  }
[00:59:18]  bb5: {
[00:59:18]      falseEdges -> [real: bb12, imaginary: bb6]; //pre_binding2
[00:59:18]  }
[00:59:18]  bb6: {
[00:59:18]      falseEdges -> [real: bb3, imaginary: bb7]; //pre_binding3
[00:59:18]  }
[00:59:18]  bb7: {
[00:59:18]      unreachable;
[00:59:18]  }
[00:59:18]  bb8: {
[00:59:18]      unreachable;
[00:59:18]  }
[00:59:18]  bb9: { // binding1 and guard
[00:59:18]      StorageLive(_5);
[00:59:18]      _5 = &((_2 as Some).0: i32);
[00:59:18]      StorageLive(_8);
[00:59:18]      _8 = const guard() -> [return: bb10, unwind: bb1];
[00:59:18]  }
[00:59:18]  bb10: { // end of guard
[00:59:18]      StorageLive(_4);
[00:59:18]      _4 = ((_2 as Some).0: i32);
[00:59:18]      switchInt(move _8) -> [false: bb11, otherwise: bb2];
[00:59:18]  }
[00:59:18]  bb11: { // to pre_binding2
[00:59:18]      falseEdges -> [real: bb5, imaginary: bb5];
[00:59:18]  }
[00:59:18]  bb12: { // bindingNoLandingPads.before.mir2 and arm2
[00:59:18]      StorageLive(_6);
[00:59:18]      _6 = ((_2 as Some).0: i32);
[00:59:18]      StorageLive(_10);
[00:59:18]      _10 = _6;
[00:59:18]      _1 = (const 2i32, move _10);
[00:59:18]      StorageDead(_10);
[00:59:18]      goto -> bb13;
[00:59:18]  }
[00:5 -> [real: bb9, imaginary: bb5];
[00:59:18]     }
[00:59:18]     bb5: {                              
[00:59:18]         falseEdges -> [real: bb12, imaginary: bb6];
[00:59:18]     }
[00:59:18]     bb6: {                              
[00:59:18]         falseEdges -> [real: bb3, imaginary: bb7];
[00:59:18]     }
[00:59:18]     bb7: {                              
[00:59:18]         unreachable;
[00:59:18]     }
[00:59:18]     bb8: {                              
[00:59:18]         unreachable;
[00:59:18]     }
[00:59:18]     bb9: {                              
[00:59:18]         StorageLive(_5);
[00:59:18]         _11 = promoted[0];
[00:59:18]         _5 = &(((*_11) as Some).0: i32);
[00:59:18]         StorageLive(_8);
[00:59:18]         _8 = const guard() -> [return: bb10, unwind: bb1];
[00:59:18]     }
[00:59:18]     bb10: {                             
[00:59:18]         StorageLive(_4);
[00:59:18]         _4 = ((_2 as Some).0: i32);
[00:59:18]         switchInt(move _8) -> [false: bb11, otherwise: bb2];
[00:59:18]     }
[00:59:18]     bb11: {                             
[00:59:18]         falseEdges -> [real: bb5, imaginary: bb5];
[00:59:18]     }
[00:59:18]     bb12: {                             
[00:59:18]         StorageLive(_6);
[00:59:18]         _6 = ((_2 as Some).0: i32);
[00:59:18]         StorageLive(_10);
[00:59:18]         _10 = _6;
[00:59:18]         _1 = (const 2i32, move _10);
[00:59:18]         StorageDead(_10);
[00:59:18]         goto -> bb13;
[00:59:18]     }
[00:59:18]     bb13: {                             
[00:59:18]         StorageDead(_6);
[00:59:18]         StorageDead(_4);
[00:59:18]         StorageDead(_8);
[00:59:18]         StorageDead(_5);
[00:59:18]         StorageDead(_1);
[00:59:18]         StorageDead(_2);
[00:59:18]         _0 = ();
[00:59:18]         return;
[00:59:18] }', tools/compiletest/src/runtest.rs:2801:13
[00:59:18] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[00:59:18] 
[00:59:18] 
[00:59:18] 
[00:59:18] failures:
[00:59:18]     [mir-opt] mir-opt/match_false_edges.rs
[00:59:18] 
[00:59:18] test result: FAILED. 49 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
[00:59:18] 
[00:59:18] 
[00:59:18] 
[00:59:18] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/mir-opt" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "mir-opt" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-3.9/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options " "--target-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "3.9.1\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[00:59:18] 
[00:59:18] 
[00:59:18] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:59:18] Build completed unsuccessfully in 0:17:06
[00:59:18] Build completed unsuccessfully in 0:17:06
[00:59:18] Makefile:58: recipe for target 'check' failed
[00:59:18] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:002d674e
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

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)

[bors]

☔ The latest upstream changes (presumably #50249) made this pull request unmergeable. Please resolve the merge conflicts.

[nikomatsakis]

It'd be nice to have an example of some Rust code where this applies, for those of us whose brains are tired

[nikomatsakis]

Can you put a comment here? What does this else indicate? I can't see it in the diff, it'll also be hard to tell when reading. Something like:

// Not a mut borrow

(Is that right? I'm guessing)

[eddyb]

Hmm maybe I should split this part into its own commit, it's a straight-forward translation of the old code, but it's mixed in with new parts.

[nikomatsakis]

@bors r+

[bors]

📌 Commit d1f117d has been approved by nikomatsakis

[bors]

⌛ Testing commit d1f117d with merge c6a1979...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing c6a1979 to master...