AssumptionCache: Update documentation comment.

The comment was somewhat misleading in that it implied that passes were not
responsible for adding new assumptions to the assumption cache. This new
wording now explicitly mentions that they are required to do so.

Differential Revision: https://reviews.llvm.org/D29977

llvm-svn: 295148

llvm/include/llvm/Analysis/AssumptionCache.h

@@ -31,11 +31,10 @@ namespace llvm {
 /// \brief A cache of @llvm.assume calls within a function.
 ///
 /// This cache provides fast lookup of assumptions within a function by caching
-/// them and amortizing the cost of scanning for them across all queries. The
-/// cache is also conservatively self-updating so that it will never return
-/// incorrect results about a function even as the function is being mutated.
-/// However, flushing the cache and rebuilding it (or explicitly updating it)
-/// may allow it to discover new assumptions.
+/// them and amortizing the cost of scanning for them across all queries. Passes
+/// that create new assumptions are required to call registerAssumption() to
+/// register any new @llvm.assume calls that they create. Deletions of
+/// @llvm.assume calls do not require special handling.
 class AssumptionCache {
   /// \brief The function for which this cache is handling assumptions.
   ///