Index: clang-tools-extra/trunk/clangd/XRefs.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/XRefs.cpp
+++ clang-tools-extra/trunk/clangd/XRefs.cpp
@@ -37,6 +37,11 @@
   return nullptr;
 }
 
+void logIfOverflow(const SymbolLocation &Loc) {
+  if (Loc.Start.hasOverflow() || Loc.End.hasOverflow())
+    log("Possible overflow in symbol location: {0}", Loc);
+}
+
 // Convert a SymbolLocation to LSP's Location.
 // HintPath is used to resolve the path of URI.
 // FIXME: figure out a good home for it, and share the implementation with
@@ -61,6 +66,7 @@
   LSPLoc.range.start.character = Loc.Start.column();
   LSPLoc.range.end.line = Loc.End.line();
   LSPLoc.range.end.character = Loc.End.column();
+  logIfOverflow(Loc);
   return LSPLoc;
 }
 
Index: clang-tools-extra/trunk/clangd/index/Index.h
===================================================================
--- clang-tools-extra/trunk/clangd/index/Index.h
+++ clang-tools-extra/trunk/clangd/index/Index.h
@@ -43,6 +43,10 @@
     void setColumn(uint32_t Column);
     uint32_t column() const { return Column; }
 
+    bool hasOverflow() const {
+      return Line >= MaxLine || Column >= MaxColumn;
+    }
+
     static constexpr uint32_t MaxLine = (1 << 20) - 1;
     static constexpr uint32_t MaxColumn = (1 << 12) - 1;
 
Index: clang-tools-extra/trunk/clangd/index/Index.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/index/Index.cpp
+++ clang-tools-extra/trunk/clangd/index/Index.cpp
@@ -23,7 +23,6 @@
 constexpr uint32_t SymbolLocation::Position::MaxColumn;
 void SymbolLocation::Position::setLine(uint32_t L) {
   if (L > MaxLine) {
-    log("Set an overflowed Line {0}", L);
     Line = MaxLine;
     return;
   }
@@ -31,7 +30,6 @@
 }
 void SymbolLocation::Position::setColumn(uint32_t Col) {
   if (Col > MaxColumn) {
-    log("Set an overflowed Column {0}", Col);
     Column = MaxColumn;
     return;
   }
Index: clang-tools-extra/trunk/unittests/clangd/IndexTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/IndexTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/IndexTests.cpp
@@ -46,10 +46,15 @@
   EXPECT_EQ(1u, Pos.line());
   Pos.setColumn(2);
   EXPECT_EQ(2u, Pos.column());
+  EXPECT_FALSE(Pos.hasOverflow());
 
   Pos.setLine(Position::MaxLine + 1); // overflow
+  EXPECT_TRUE(Pos.hasOverflow());
   EXPECT_EQ(Pos.line(), Position::MaxLine);
+  Pos.setLine(1); // reset the overflowed line.
+
   Pos.setColumn(Position::MaxColumn + 1); // overflow
+  EXPECT_TRUE(Pos.hasOverflow());
   EXPECT_EQ(Pos.column(), Position::MaxColumn);
 }