Resolver: Reduce number of hash function call.

This is yet another optimization patch. Previously we called
SymbolTable::isDefined() and SymbolTable::findByName() from a very
frequently executed function. Because isDefined calls findByName,
findByName is called twice on each iteration.

findByName is not a cheap function. It computes a hash value for a
given symbol name. When linking C++ programs, it can be expensive
because of C++ mangled long symbols.

This patch reduces the number of call from 2 to 1. Performance
improvements by this patch was larger than I expected. Linking time
of chrome.dll gets almost 5% shorter.

llvm-svn: 231549

1 files changed, 2 insertions, 2 deletions

diff --git a/lld/lib/Core/Resolver.cpp b/lld/lib/Core/Resolver.cpp
index fbfffb5aa8c..bb942f54b70 100644
--- a/lld/lib/Core/Resolver.cpp
+++ b/lld/lib/Core/Resolver.cpp
@@ -54,8 +54,8 @@ void Resolver::forEachUndefines(File &file, bool searchForOverrides,
       StringRef undefName = _undefines[i];
       if (undefName.empty())
         continue;
-      if (_symbolTable.isDefined(undefName) ||
-          _symbolTable.isCoalescedAway(_symbolTable.findByName(undefName))) {
+      const Atom *atom = _symbolTable.findByName(undefName);
+      if (!isa<UndefinedAtom>(atom) || _symbolTable.isCoalescedAway(atom)) {
         // The symbol was resolved by some other file. Cache the result.
         _undefines[i] = "";
         continue;