BasicAA: update comments in a routine (NFC) (llvm#110492)

The comments in isObjectSmallerThan are outdated, as it is only ever
called with the underlying object as the first argument. Update the
comments to reflect this.

Author: artagnon

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -117,7 +117,8 @@ static std::optional<TypeSize> getObjectSize(const Value *V,
 }
 
 /// Returns true if we can prove that the object specified by V is smaller than
-/// Size.
+/// Size. Bails out early unless the root object is passed as the first
+/// parameter.
 static bool isObjectSmallerThan(const Value *V, TypeSize Size,
                                 const DataLayout &DL,
                                 const TargetLibraryInfo &TLI,
@@ -134,20 +135,14 @@ static bool isObjectSmallerThan(const Value *V, TypeSize Size,
   //     char *p = (char*)malloc(100)
   //     char *q = p+80;
   //
-  //  In the context of c1 and c2, the "object" pointed by q refers to the
+  // In the context of c1 and c2, the "object" pointed by q refers to the
   // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
   //
-  //  However, in the context of c3, the "object" refers to the chunk of memory
-  // being allocated. So, the "object" has 100 bytes, and q points to the middle
-  // the "object". In case q is passed to isObjectSmallerThan() as the 1st
-  // parameter, before the llvm::getObjectSize() is called to get the size of
-  // entire object, we should:
-  //    - either rewind the pointer q to the base-address of the object in
-  //      question (in this case rewind to p), or
-  //    - just give up. It is up to caller to make sure the pointer is pointing
-  //      to the base address the object.
-  //
-  // We go for 2nd option for simplicity.
+  // In the context of c3, the "object" refers to the chunk of memory being
+  // allocated. So, the "object" has 100 bytes, and q points to the middle the
+  // "object". However, unless p, the root object, is passed as the first
+  // parameter, the call to isIdentifiedObject() makes isObjectSmallerThan()
+  // bail out early.
   if (!isIdentifiedObject(V))
     return false;