[CaptureTracking][NFC] Clarify usage expectations in PointerMayBeCaptured comments

The comments for PointerMayBeCaptured and related APIs have been
updated to explicitly state that these functions assume the input is an
function-local object. It is the caller's responsibility to ensure this
precondition is met. This clarification aligns with recent discussions
and feedback from code reviews, aiming to prevent misuse and potential
analysis errors.

Author: Camsyn

llvm/include/llvm/Analysis/CaptureTracking.h

@@ -41,13 +41,17 @@ namespace llvm {
   /// MaxUsesToExplore specifies how many uses the analysis should explore for
   /// one value before giving up due too "too many uses". If MaxUsesToExplore
   /// is zero, a default value is assumed.
+  /// This assumes the pointer is to a function-local object. The caller is
+  /// responsible for ensuring this.
   bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures,
                             unsigned MaxUsesToExplore = 0);
 
   /// Return which components of the pointer may be captured. Only consider
   /// components that are part of \p Mask. Once \p StopFn on the accumulated
   /// components returns true, the traversal is aborted early. By default, this
   /// happens when *any* of the components in \p Mask are captured.
+  /// This assumes the pointer is to a function-local object. The caller is
+  /// responsible for ensuring this.
   CaptureComponents PointerMayBeCaptured(
       const Value *V, bool ReturnCaptures, CaptureComponents Mask,
       function_ref<bool(CaptureComponents)> StopFn = capturesAnything,
@@ -64,6 +68,8 @@ namespace llvm {
   /// MaxUsesToExplore specifies how many uses the analysis should explore for
   /// one value before giving up due too "too many uses". If MaxUsesToExplore
   /// is zero, a default value is assumed.
+  /// This assumes the pointer is to a function-local object. The caller is
+  /// responsible for ensuring this.
   bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
                                   const Instruction *I, const DominatorTree *DT,
                                   bool IncludeI = false,
@@ -184,6 +190,8 @@ namespace llvm {
   /// MaxUsesToExplore specifies how many uses the analysis should explore for
   /// one value before giving up due too "too many uses". If MaxUsesToExplore
   /// is zero, a default value is assumed.
+  /// This assumes the pointer is to a function-local object. The caller is
+  /// responsible for ensuring this.
   void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
                             unsigned MaxUsesToExplore = 0);