Explicit notation.

Author: cjgillot

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -18,7 +18,8 @@
 //!   into `Goto { target }`.
 //!
 //! In this file, we denote as `place ?= value` the existence of a replacement condition
-//! on `place` with given `value`.
+//! on `place` with given `value`, irrespective of the polarity and target of that
+//! replacement condition.
 //!
 //! We then walk the CFG backwards transforming the set of conditions.
 //! When we find a fulfilling assignment, we record a `ThreadingOpportunity`.