[clang] NFC: Extract lower-level SourceManager functions

[jansvoboda11]

Summary

This is a prep-patch for D136624 which allows querying SourceManager with raw offsets instead of SourceLocations.

[dexonsmith]

LGTM.

clang/include/clang/Basic/SourceManager.h

public:
 
   /// Return the FileID for a SourceLocation.
   ///
   /// This is a very hot method that is used for all SourceManager queries
   /// that start with a SourceLocation object.  It is responsible for finding
   /// the entry in SLocEntryTable which contains the specified location.
   ///
   FileID getFileID(SourceLocation SpellingLoc) const {
-    SourceLocation::UIntTy SLocOffset = SpellingLoc.getOffset();
-
-    // If our one-entry cache covers this offset, just return it.
-    if (isOffsetInFileID(LastFileIDLookup, SLocOffset))
-      return LastFileIDLookup;
-
-    return getFileIDSlow(SLocOffset);
+    return getFileID(SpellingLoc.getOffset());
   }
 
   /// Return the filename of the file containing a SourceLocation.
   StringRef getFilename(SourceLocation SpellingLoc) const;
 
   /// Return the source location corresponding to the first byte of
   /// the specified file.
   SourceLocation getLocForStartOfFile(FileID FID) const {
public:
   /// in the global source view. The lowest ID and the base offset of the
   /// entries will be returned.
   std::pair<int, SourceLocation::UIntTy>
   AllocateLoadedSLocEntries(unsigned NumSLocEntries,
                             SourceLocation::UIntTy TotalSize);
 
   /// Returns true if \p Loc came from a PCH/Module.
   bool isLoadedSourceLocation(SourceLocation Loc) const {
-    return Loc.getOffset() >= CurrentLoadedOffset;
+    return isLoadedOffset(Loc.getOffset());
   }
 
   /// Returns true if \p Loc did not come from a PCH/Module.
   bool isLocalSourceLocation(SourceLocation Loc) const {
-    return Loc.getOffset() < NextLocalOffset;
+    return isLocalOffset(Loc.getOffset());
   }
 
   /// Returns true if \p FID came from a PCH/Module.
   bool isLoadedFileID(FileID FID) const {
     assert(FID.ID != -1 && "Using FileID sentinel value");
     return FID.ID < 0;
   }
 
const SrcMgr::SLocEntry &getSLocEntryByID(int ID,
     return getLocalSLocEntry(static_cast<unsigned>(ID));
   }
 
   const SrcMgr::SLocEntry &
   getLoadedSLocEntryByID(int ID, bool *Invalid = nullptr) const {
     return getLoadedSLocEntry(static_cast<unsigned>(-ID - 2), Invalid);
   }
 
+  FileID getFileID(SourceLocation::UIntTy SLocOffset) const {
+    // If our one-entry cache covers this offset, just return it.
+    if (isOffsetInFileID(LastFileIDLookup, SLocOffset))
+      return LastFileIDLookup;
+
+    return getFileIDSlow(SLocOffset);
+  }
+
+  bool isLocalOffset(SourceLocation::UIntTy SLocOffset) const {
+    return SLocOffset < CurrentLoadedOffset;
+  }
+
+  bool isLoadedOffset(SourceLocation::UIntTy SLocOffset) const {
+    return SLocOffset >= CurrentLoadedOffset;
+  }
+
   /// Implements the common elements of storing an expansion info struct into
   /// the SLocEntry table and producing a source location that refers to it.
   SourceLocation
   createExpansionLocImpl(const SrcMgr::ExpansionInfo &Expansion,
                          unsigned Length, int LoadedID = 0,
                          SourceLocation::UIntTy LoadedOffset = 0);
 
   /// Return true if the specified FileID contains the