[MC][COFF] Emit weak symbols to the correct section. Patch by Dmitry Puzirev!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167877 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 8f5d770..2ee9436 100644
--- a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -701,8 +701,19 @@
 const MCSection *TargetLoweringObjectFileCOFF::
 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
                          Mangler *Mang, const TargetMachine &TM) const {
-  return getContext().getCOFFSection(GV->getSection(),
-                                     getCOFFSectionFlags(Kind),
+  int Selection = 0;
+  unsigned Characteristics = getCOFFSectionFlags(Kind);
+  SmallString<128> Name(GV->getSection().c_str());
+  if (GV->isWeakForLinker()) {
+    Selection = COFF::IMAGE_COMDAT_SELECT_ANY;
+    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
+    MCSymbol *Sym = Mang->getSymbol(GV);
+    Name.append("$");
+    Name.append(Sym->getName().begin() + 1, Sym->getName().end());
+  }
+  return getContext().getCOFFSection(Name,
+                                     Characteristics,
+                                     Selection,
                                      Kind);
 }