WinCOFFObjectWriter: optimize the string table for common suffices

This is a follow-up from r207670 which did the same for ELF.

Differential Revision: http://reviews.llvm.org/D5530

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218636 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/StringTableBuilder.cpp

@@ -9,6 +9,8 @@
 
 #include "llvm/MC/StringTableBuilder.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/COFF.h"
+#include "llvm/Support/Endian.h"
 
 using namespace llvm;
 
@@ -25,19 +27,28 @@ static bool compareBySuffix(StringRef a, StringRef b) {
   return sizeA > sizeB;
 }
 
-void StringTableBuilder::finalize() {
+void StringTableBuilder::finalize(Kind kind) {
   SmallVector<StringRef, 8> Strings;
+  Strings.reserve(StringIndexMap.size());
+
   for (auto i = StringIndexMap.begin(), e = StringIndexMap.end(); i != e; ++i)
     Strings.push_back(i->getKey());
 
   std::sort(Strings.begin(), Strings.end(), compareBySuffix);
 
-  // FIXME: Starting with a null byte is ELF specific. Generalize this so we
-  // can use the class with other object formats.
-  StringTable += '\x00';
+  if (kind == ELF) {
+    // Start the table with a NUL byte.
+    StringTable += '\x00';
+  } else if (kind == WinCOFF) {
+    // Make room to write the table size later.
+    StringTable.append(4, '\x00');
+  }
 
   StringRef Previous;
   for (StringRef s : Strings) {
+    if (kind == WinCOFF)
+      assert(s.size() > COFF::NameSize && "Short string in COFF string table!");
+
     if (Previous.endswith(s)) {
       StringIndexMap[s] = StringTable.size() - 1 - s.size();
       continue;
@@ -48,4 +59,16 @@ void StringTableBuilder::finalize() {
     StringTable += '\x00';
     Previous = s;
   }
+
+  if (kind == WinCOFF) {
+    assert(StringTable.size() <= std::numeric_limits<uint32_t>::max());
+    uint32_t size = static_cast<uint32_t>(StringTable.size());
+    support::endian::write<uint32_t, support::little, support::unaligned>(
+        StringTable.data(), size);
+  }
+}
+
+void StringTableBuilder::clear() {
+  StringTable.clear();
+  StringIndexMap.clear();
 }