[LoopInfo] Clarify description of makeLoopInvariant. NFC.

[SjoerdMeijer]

Summary

Clarify that Changed is set to true if the instruction/value was made loop-invariant; the function is returning true if it was already invariant.

llvm/include/llvm/Analysis/LoopInfo.h

public:
   bool isLoopInvariant(const Value *V) const;
 
   /// Return true if all the operands of the specified instruction are loop
   /// invariant.
   bool hasLoopInvariantOperands(const Instruction *I) const;
 
   /// If the given value is an instruction inside of the loop and it can be
   /// hoisted, do so to make it trivially loop-invariant.
-  /// Return true if the value after any hoisting is loop invariant. This
-  /// function can be used as a slightly more aggressive replacement for
-  /// isLoopInvariant.
+  /// Return true if \c V is already loop-invariant, and false if \c V can't
+  /// be made loop-invariant. If \c V is made loop-invariant, \c Changed is
+  /// set to true. This function can be used as a slightly more aggressive
+  /// replacement for isLoopInvariant.
   ///
   /// If InsertPt is specified, it is the point to hoist instructions to.
   /// If null, the terminator of the loop preheader is used.
+  ///
   bool makeLoopInvariant(Value *V, bool &Changed,
                          Instruction *InsertPt = nullptr,
                          MemorySSAUpdater *MSSAU = nullptr) const;
 
   /// If the given instruction is inside of the loop and it can be hoisted, do
   /// so to make it trivially loop-invariant.
-  /// Return true if the instruction after any hoisting is loop invariant. This
-  /// function can be used as a slightly more aggressive replacement for
-  /// isLoopInvariant.
+  /// Return true if \c I is already loop-invariant, and false if \c I can't
+  /// be made loop-invariant. If \c I is made loop-invariant, \c Changed is
+  /// set to true. This function can be used as a slightly more aggressive
+  /// replacement for isLoopInvariant.
   ///
   /// If InsertPt is specified, it is the point to hoist instructions to.
   /// If null, the terminator of the loop preheader is used.
   ///
   bool makeLoopInvariant(Instruction *I, bool &Changed,
                          Instruction *InsertPt = nullptr,
                          MemorySSAUpdater *MSSAU = nullptr) const;