[lld] r315664 - Add comment.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Thu Oct 12 19:57:59 2017
New Revision: 315664

URL: http://llvm.org/viewvc/llvm-project?rev=315664&view=rev
Log:
Add comment.

Modified:
    lld/trunk/ELF/Symbols.cpp

Modified: lld/trunk/ELF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=315664&r1=315663&r2=315664&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.cpp (original)
+++ lld/trunk/ELF/Symbols.cpp Thu Oct 12 19:57:59 2017
@@ -126,10 +126,18 @@ SymbolBody::SymbolBody(Kind K, StringRef
       IsInIgot(false), IsPreemptible(false), Type(Type), StOther(StOther),
       Name(Name) {}
 
+// Returns true if this is a weak undefined symbol.
 bool SymbolBody::isUndefWeak() const {
-  if (isLocal())
-    return false;
-  return symbol()->isWeak() && (isUndefined() || isLazy());
+  // A note on isLazy() in the following expression: If you add a weak
+  // undefined symbol and then a lazy symbol to the symbol table, the
+  // combined result is a lazy weak symbol. isLazy is for that sitaution.
+  //
+  // Weak undefined symbols shouldn't fetch archive members (for
+  // compatibility with other linkers), but we still want to memorize
+  // that there are lazy symbols, because strong undefined symbols
+  // could be added later which triggers archive member fetching.
+  // Thus, the weak lazy symbol is a valid concept in lld.
+  return !isLocal() && symbol()->isWeak() && (isUndefined() || isLazy());
 }
 
 InputFile *SymbolBody::getFile() const {