AssumptionCache: Update documentation comment.

[pcc]

Summary

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.

[chandlerc]

I would still mention that deleting them is fine.

Also, I strongly suspect there are many more bugs lurking like the one you hit...

[pcc]

• Mention that deletions are fine

[hfinkel]

llvm/include/llvm/Analysis/AssumptionCache.h

35

This should just read, "passes that create new assumption are required to...".

[pcc]

• Adopt suggested wording

[hfinkel]

LGTM

llvm/include/llvm/Analysis/AssumptionCache.h

 #include "llvm/Pass.h"
 #include <memory>
 
 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 use the assumption cache are required to call registerAssumption() to
+/// register any new @llvm.assume calls that they create.
 class AssumptionCache {
   /// \brief The function for which this cache is handling assumptions.
   ///
   /// We track this to lazily populate our assumptions.
   Function &F;
 
   /// \brief Vector of weak value handles to calls of the @llvm.assume
   /// intrinsic.