Use SmallVec in TokenStreamBuilder.

[nnethercote]

This reduces by 12% the number of allocations done for a "clean incremental" of webrender_api, which reduces the instruction count by about 0.5%.

r? @petrochenkov

[petrochenkov]

@bors try

[bors]

⌛ Trying commit 08df22a905333c0384b36ef4bdcdec842324677f with merge 58625519613b737ca78737fa9055ab1160d45ba8...

[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:052f5e9a:start=1553750927572300497,finish=1553751065547230830,duration=137974930333
$ 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
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:23:08] 
[01:23:08] running 9 tests
[01:23:08] iiiiiiiii
[01:23:08] 
[01:23:08]  finished in 0.168
[01:23:08] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:23:25] 
[01:23:25] running 120 tests
[01:23:55] .iiiii...i.....i..i...i..i.i...i.ii...i.....i..i....i..........iiii..........i...ii...i.......ii.i.i 100/120
[01:24:00] .i......iii.i.....ii
[01:24:00] 
[01:24:00]  finished in 34.859
[01:24:00] travis_fold:end:test_debuginfo

---
travis_time:start:test_stage1-syntax
Testing syntax stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:48:55]    Compiling syntax v0.0.0 (/checkout/src/libsyntax)
[01:49:06] error[E0308]: mismatched types
[01:49:06]    --> <::alloc::macros::vec macros>:3:1
[01:49:06]     |
[01:49:06] 1   | / ( $ elem : expr ; $ n : expr ) => (
[01:49:06] 2   | | $ crate :: vec :: from_elem ( $ elem , $ n ) ) ; ( $ ( $ x : expr ) , * ) => (
[01:49:06] 3   | | < [ _ ] > :: into_vec ( box [ $ ( $ x ) , * ] ) ) ; ( $ ( $ x : expr , ) * )
[01:49:06]     | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[01:49:06]     | | expected struct `smallvec::SmallVec`, found struct `std::vec::Vec`
[01:49:06]     | | expected struct `smallvec::SmallVec`, found struct `std::vec::Vec`
[01:49:06] 4   | | => ( vec ! [ $ ( $ x ) , * ] )
[01:49:06]     | 
[01:49:06]    ::: src/libsyntax/tokenstream.rs:577:52
[01:49:06]     |
[01:49:06]     |
[01:49:06] 577 |               let eq_res = TokenStream::from_streams(vec![test_fst, test_snd]);
[01:49:06]     |
[01:49:06]     |
[01:49:06]     = note: expected type `smallvec::SmallVec<[tokenstream::TokenStream; 2]>`
[01:49:06]                found type `std::vec::Vec<tokenstream::TokenStream>`
[01:49:07] error: aborting due to previous error
[01:49:07] 
[01:49:07] For more information about this error, try `rustc --explain E0308`.
[01:49:07] error: Could not compile `syntax`.
[01:49:07] error: Could not compile `syntax`.
[01:49:07] 
[01:49:07] To learn more, run the command again with --verbose.
[01:49:07] 
[01:49:07] 
[01:49:07] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "-p" "syntax" "--" "--quiet"
[01:49:07] 
[01:49:07] 
[01:49:07] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:49:07] Build completed unsuccessfully in 0:38:41
[01:49:07] Build completed unsuccessfully in 0:38:41
[01:49:07] make: *** [check] Error 1
[01:49:07] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:327d7648
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Thu Mar 28 07:20:23 UTC 2019

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]

☀️ Try build successful - checks-travis
Build commit: 58625519613b737ca78737fa9055ab1160d45ba8

[nnethercote]

@rust-timer build 58625519613b737ca78737fa9055ab1160d45ba8

[rust-timer]

Success: Queued 58625519613b737ca78737fa9055ab1160d45ba8 with parent d20e000, comparison URL.

[rust-timer]

Finished benchmarking try commit 58625519613b737ca78737fa9055ab1160d45ba8

[petrochenkov]

r=me with libsyntax tests fixed

[nnethercote]

I fixed the libsyntax test.

@bors r=petrochenkov

[bors]

📌 Commit 17a8aff has been approved by petrochenkov