Index: llvm/trunk/include/llvm/MC/MCSectionCOFF.h
===================================================================
--- llvm/trunk/include/llvm/MC/MCSectionCOFF.h
+++ llvm/trunk/include/llvm/MC/MCSectionCOFF.h
@@ -84,6 +84,10 @@
     return WinCFISectionID;
   }
 
+  static bool isImplicitlyDiscardable(StringRef Name) {
+    return Name.startswith(".debug");
+  }
+
   static bool classof(const MCSection *S) { return S->getVariant() == SV_COFF; }
 };
 
Index: llvm/trunk/lib/MC/MCParser/COFFAsmParser.cpp
===================================================================
--- llvm/trunk/lib/MC/MCParser/COFFAsmParser.cpp
+++ llvm/trunk/lib/MC/MCParser/COFFAsmParser.cpp
@@ -41,7 +41,8 @@
                           COFF::COMDATType Type);
 
   bool ParseSectionName(StringRef &SectionName);
-  bool ParseSectionFlags(StringRef FlagsString, unsigned* Flags);
+  bool ParseSectionFlags(StringRef SectionName, StringRef FlagsString,
+                         unsigned *Flags);
 
   void Initialize(MCAsmParser &Parser) override {
     // Call the base implementation.
@@ -155,17 +156,19 @@
   return SectionKind::getData();
 }
 
-bool COFFAsmParser::ParseSectionFlags(StringRef FlagsString, unsigned* Flags) {
+bool COFFAsmParser::ParseSectionFlags(StringRef SectionName,
+                                      StringRef FlagsString, unsigned *Flags) {
   enum {
-    None      = 0,
-    Alloc     = 1 << 0,
-    Code      = 1 << 1,
-    Load      = 1 << 2,
-    InitData  = 1 << 3,
-    Shared    = 1 << 4,
-    NoLoad    = 1 << 5,
-    NoRead    = 1 << 6,
-    NoWrite  =  1 << 7
+    None        = 0,
+    Alloc       = 1 << 0,
+    Code        = 1 << 1,
+    Load        = 1 << 2,
+    InitData    = 1 << 3,
+    Shared      = 1 << 4,
+    NoLoad      = 1 << 5,
+    NoRead      = 1 << 6,
+    NoWrite     = 1 << 7,
+    Discardable = 1 << 8,
   };
 
   bool ReadOnlyRemoved = false;
@@ -198,6 +201,10 @@
       SecFlags &= ~Load;
       break;
 
+    case 'D': // discardable
+      SecFlags |= Discardable;
+      break;
+
     case 'r': // read-only
       ReadOnlyRemoved = false;
       SecFlags |= NoWrite;
@@ -249,6 +256,9 @@
     *Flags |= COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA;
   if (SecFlags & NoLoad)
     *Flags |= COFF::IMAGE_SCN_LNK_REMOVE;
+  if ((SecFlags & Discardable) ||
+      MCSectionCOFF::isImplicitlyDiscardable(SectionName))
+    *Flags |= COFF::IMAGE_SCN_MEM_DISCARDABLE;
   if ((SecFlags & NoRead) == 0)
     *Flags |= COFF::IMAGE_SCN_MEM_READ;
   if ((SecFlags & NoWrite) == 0)
@@ -326,7 +336,8 @@
 //   a: Ignored.
 //   b: BSS section (uninitialized data)
 //   d: data section (initialized data)
-//   n: Discardable section
+//   n: "noload" section (removed by linker)
+//   D: Discardable section
 //   r: Readable section
 //   s: Shared section
 //   w: Writable section
@@ -353,7 +364,7 @@
     StringRef FlagsStr = getTok().getStringContents();
     Lex();
 
-    if (ParseSectionFlags(FlagsStr, &Flags))
+    if (ParseSectionFlags(SectionName, FlagsStr, &Flags))
       return true;
   }
 
Index: llvm/trunk/lib/MC/MCSectionCOFF.cpp
===================================================================
--- llvm/trunk/lib/MC/MCSectionCOFF.cpp
+++ llvm/trunk/lib/MC/MCSectionCOFF.cpp
@@ -64,6 +64,9 @@
     OS << 'n';
   if (getCharacteristics() & COFF::IMAGE_SCN_MEM_SHARED)
     OS << 's';
+  if ((getCharacteristics() & COFF::IMAGE_SCN_MEM_DISCARDABLE) &&
+      !isImplicitlyDiscardable(SectionName))
+    OS << 'D';
   OS << '"';
 
   if (getCharacteristics() & COFF::IMAGE_SCN_LNK_COMDAT) {
Index: llvm/trunk/test/MC/COFF/section.s
===================================================================
--- llvm/trunk/test/MC/COFF/section.s
+++ llvm/trunk/test/MC/COFF/section.s
@@ -30,6 +30,7 @@
 .section s_a,"a"; .long 1
 .section s_b,"b"; .long 1
 .section s_d,"d"; .long 1
+.section s_D,"D"; .long 1
 .section s_n,"n"; .long 1
 .section s_r,"r"; .long 1
 .section s_s,"s"; .long 1
@@ -83,6 +84,15 @@
 // CHECK-NEXT:     ]
 // CHECK:        }
 // CHECK:        Section {
+// CHECK:          Name: s_D
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
+// CHECK-NEXT:       IMAGE_SCN_MEM_DISCARDABLE
+// CHECK-NEXT:       IMAGE_SCN_MEM_READ
+// CHECK-NEXT:       IMAGE_SCN_MEM_WRITE
+// CHECK-NEXT:     ]
+// CHECK:        }
+// CHECK:        Section {
 // CHECK:          Name: s_n
 // CHECK:          Characteristics [
 // CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
@@ -167,4 +177,18 @@
 // CHECK-NEXT:     ]
 // CHECK:        }
 
+// Sections starting with ".debug" are implicitly discardable. This is
+// compatible with gas.
+.section .debug_asdf,"dr"; .long 1
+// CHECK:        Section {
+// CHECK:          Name: .debug_asdf
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
+// CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA
+// CHECK-NEXT:       IMAGE_SCN_MEM_DISCARDABLE
+// CHECK-NEXT:       IMAGE_SCN_MEM_READ
+// CHECK-NEXT:     ]
+// CHECK:        }
+
+
 // CHECK:      ]