[PATCH] Clarify wording in the LangRef around !invariant.load

[hfinkel at anl.gov]

> which can be assumed unchanged by any store.

First, "unchanged by any store" seems redundant (and over-specific); "unchanged" would be fine.

However, this leaves open the question of when and for how long? Does it imply invariance only during the execution of the function? or must it have the same value during every invocation? At what point does the invariance start?

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Comment at: docs/LangRef.rst:5216
@@ -5215,1 +5215,3 @@
+the location is known dereferenceable along a particular execution
+path that it's value is henceforth unchanging.  
 
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it's -> its

http://reviews.llvm.org/D6346