Add support for subsections to the ELF assembler. Fixes PR8717.

Differential Revision: http://llvm-reviews.chandlerc.com/D598

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179725 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCSectionELF.cpp b/lib/MC/MCSectionELF.cpp
index 0775cfa..bf1a984 100644
--- a/lib/MC/MCSectionELF.cpp
+++ b/lib/MC/MCSectionELF.cpp
@@ -10,6 +10,7 @@
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/raw_ostream.h"
@@ -32,10 +33,14 @@
 }
 
 void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI,
-                                        raw_ostream &OS) const {
+                                        raw_ostream &OS,
+                                        const MCExpr *Subsection) const {
 
   if (ShouldOmitSectionDirective(SectionName, MAI)) {
-    OS << '\t' << getSectionName() << '\n';
+    OS << '\t' << getSectionName();
+    if (Subsection)
+      OS << '\t' << *Subsection;
+    OS << '\n';
     return;
   }
 
@@ -129,6 +134,9 @@
   if (Flags & ELF::SHF_GROUP)
     OS << "," << Group->getName() << ",comdat";
   OS << '\n';
+
+  if (Subsection)
+    OS << "\t.subsection\t" << *Subsection << '\n';
 }
 
 bool MCSectionELF::UseCodeAlign() const {