Enabled parallel queries for perf.rlo benchmarking.

Author: michaelwoerister

src/ci/docker/dist-x86_64-linux/Dockerfile

@@ -102,6 +102,7 @@ ENV RUST_CONFIGURE_ARGS \
       --set target.x86_64-unknown-linux-gnu.ar=/rustroot/bin/llvm-ar \
       --set target.x86_64-unknown-linux-gnu.ranlib=/rustroot/bin/llvm-ranlib \
       --set llvm.thin-lto=true \
+      --enable-experimental-parallel-queries \
       --set rust.jemalloc
 ENV SCRIPT python2.7 ../x.py dist --host $HOSTS --target $HOSTS
 ENV CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER=clang

src/librustc/session/config.rs

@@ -1190,7 +1190,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "prints the llvm optimization passes being run"),
     ast_json: bool = (false, parse_bool, [UNTRACKED],
         "print the AST as JSON and halt"),
-    query_threads: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
+    query_threads: Option<usize> = (Some(4), parse_opt_uint, [UNTRACKED],
         "execute queries on a thread pool with N threads"),
     ast_json_noexpand: bool = (false, parse_bool, [UNTRACKED],
         "print the pre-expansion AST as JSON and halt"),