Merge pull request #11838 from gottesmm/pr-ca32e200fc7885a008468272cf6a7609d02fe2aa

Author: swift-ci

include/swift/SILOptimizer/Utils/Devirtualize.h

@@ -31,6 +31,7 @@
 #include "llvm/ADT/ArrayRef.h"
 
 namespace swift {
+
 /// A pair representing results of devirtualization.
 ///  - The first element is the value representing the result of the
 ///    devirtualized call.
@@ -41,6 +42,10 @@ namespace swift {
 /// Two elements are required, because a result of the new devirtualized
 /// apply/try_apply instruction (second element) eventually needs to be
 /// casted to produce a properly typed value (first element).
+///
+/// *NOTE* The reason why we use a ValueBase here instead of a SILInstruction is
+/// that a devirtualization result may be a BB arg if there was a cast in
+/// between optional types.
 typedef std::pair<ValueBase *, ApplySite> DevirtualizationResult;
 
 DevirtualizationResult tryDevirtualizeApply(ApplySite AI,