Don't enqueue onto a disabled dep_graph.

This commit guards all calls to `DepGraphThreadData::enqueue` with a
check to make sure it is enabled. This requires distinguishing between a
"fully enabled" and an "enqueue-enabled" graph.

This change avoids some useless allocation and vector manipulations when
the graph is disabled (i.e. when incremental compilation is off) which
improves speed by ~1% on some of the rustc-benchmarks.

0 files changed, 0 insertions, 0 deletions