[do not merge] Remove parallel code

[Zoxc]

Checking performance overhead of doing so.

[rust-highfive]

r? @petrochenkov

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[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.

Click to expand the log.

travis_time:end:0157788e:start=1554247458243586692,finish=1554247533061860588,duration=74818273896
$ 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
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
Setting environment variables from .travis.yml
---
[00:03:34] tidy error: /checkout/src/librustc_data_structures/sync.rs:314: trailing whitespace
[00:03:36] some tidy checks failed
[00:03:36] 
[00:03:36] 
[00:03:36] 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"
[00:03:36] 
[00:03:36] 
[00:03:36] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:36] Build completed unsuccessfully in 0:00:44
[00:03:36] Build completed unsuccessfully in 0:00:44
[00:03:36] make: *** [tidy] Error 1
[00:03:36] Makefile:67: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:19df0742
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Apr  2 23:29:18 UTC 2019
---
travis_time:end:0325a664:start=1554247759130665778,finish=1554247759135396201,duration=4730423
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:012b973c
$ 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:016d8557
travis_time:start:016d8557
$ 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:002782d8
$ 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)

[Zoxc]

@bors try

[bors]

⌛ Trying commit de242c9 with merge 7ace89a75bf08f2891adb4ce99dc9fe294237647...

[bors]

☀️ Try build successful - checks-travis
Build commit: 7ace89a75bf08f2891adb4ce99dc9fe294237647

[Zoxc]

@rust-timer build 7ace89a75bf08f2891adb4ce99dc9fe294237647

[rust-timer]

Success: Queued 7ace89a75bf08f2891adb4ce99dc9fe294237647 with parent 7641873, comparison URL.

[rust-timer]

Finished benchmarking try commit 7ace89a75bf08f2891adb4ce99dc9fe294237647