Avoid costly `show(cfg)`
Avoid costly `show(cfg)`

Summary: Unless tracing the result is not used. So make it conditional (assuming that the trace level does not change).

Reviewed By: wsanville

Differential Revision: D34431594

fbshipit-source-id: a9ff51d7c439df4c825cb58759bf382875ded047

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex