Index: cfe/trunk/lib/CodeGen/BackendUtil.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/BackendUtil.cpp
+++ cfe/trunk/lib/CodeGen/BackendUtil.cpp
@@ -1447,6 +1447,9 @@
   case Triple::Wasm:
   case Triple::UnknownObjectFormat:
     return ".llvmbc";
+  case Triple::XCOFF:
+    llvm_unreachable("XCOFF is not yet implemented");
+    break;
   }
   llvm_unreachable("Unimplemented ObjectFormatType");
 }
@@ -1460,6 +1463,9 @@
   case Triple::Wasm:
   case Triple::UnknownObjectFormat:
     return ".llvmcmd";
+  case Triple::XCOFF:
+    llvm_unreachable("XCOFF is not yet implemented");
+    break;
   }
   llvm_unreachable("Unimplemented ObjectFormatType");
 }
Index: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp
@@ -4406,6 +4406,8 @@
   switch (Triple.getObjectFormat()) {
   case llvm::Triple::UnknownObjectFormat:
     llvm_unreachable("unknown file format");
+  case llvm::Triple::XCOFF:
+    llvm_unreachable("XCOFF is not yet implemented");
   case llvm::Triple::COFF:
   case llvm::Triple::ELF:
   case llvm::Triple::Wasm:
Index: lldb/trunk/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
===================================================================
--- lldb/trunk/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ lldb/trunk/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -2059,6 +2059,7 @@
 
         assert(triple.getObjectFormat() != llvm::Triple::UnknownObjectFormat);
         assert(triple.getObjectFormat() != llvm::Triple::Wasm);
+        assert(triple.getObjectFormat() != llvm::Triple::XCOFF);
         switch (triple.getObjectFormat()) {
         case llvm::Triple::MachO:
           m_process_arch.SetArchitecture(eArchTypeMachO, cpu, sub);
@@ -2070,6 +2071,7 @@
           m_process_arch.SetArchitecture(eArchTypeCOFF, cpu, sub);
           break;
         case llvm::Triple::Wasm:
+        case llvm::Triple::XCOFF:
           if (log)
             log->Printf("error: not supported target architecture");
           return false;
Index: llvm/trunk/include/llvm/ADT/Triple.h
===================================================================
--- llvm/trunk/include/llvm/ADT/Triple.h
+++ llvm/trunk/include/llvm/ADT/Triple.h
@@ -219,6 +219,7 @@
     ELF,
     MachO,
     Wasm,
+    XCOFF,
   };
 
 private:
@@ -598,6 +599,11 @@
            !isAndroid();
   }
 
+  /// Tests whether the OS is AIX.
+  bool isOSAIX() const {
+    return getOS() == Triple::AIX;
+  }
+
   /// Tests whether the OS uses the ELF binary format.
   bool isOSBinFormatELF() const {
     return getObjectFormat() == Triple::ELF;
@@ -618,6 +624,11 @@
     return getObjectFormat() == Triple::Wasm;
   }
 
+  /// Tests whether the OS uses the XCOFF binary format.
+  bool isOSBinFormatXCOFF() const {
+    return getObjectFormat() == Triple::XCOFF;
+  }
+
   /// Tests whether the target is the PS4 CPU
   bool isPS4CPU() const {
     return getArch() == Triple::x86_64 &&
Index: llvm/trunk/include/llvm/MC/MCObjectFileInfo.h
===================================================================
--- llvm/trunk/include/llvm/MC/MCObjectFileInfo.h
+++ llvm/trunk/include/llvm/MC/MCObjectFileInfo.h
@@ -380,7 +380,7 @@
     return EHFrameSection;
   }
 
-  enum Environment { IsMachO, IsELF, IsCOFF, IsWasm };
+  enum Environment { IsMachO, IsELF, IsCOFF, IsWasm, IsXCOFF };
   Environment getObjectFileType() const { return Env; }
 
   bool isPositionIndependent() const { return PositionIndependent; }
Index: llvm/trunk/lib/MC/MCContext.cpp
===================================================================
--- llvm/trunk/lib/MC/MCContext.cpp
+++ llvm/trunk/lib/MC/MCContext.cpp
@@ -161,6 +161,9 @@
       return new (Name, *this) MCSymbolMachO(Name, IsTemporary);
     case MCObjectFileInfo::IsWasm:
       return new (Name, *this) MCSymbolWasm(Name, IsTemporary);
+    case MCObjectFileInfo::IsXCOFF:
+      // TODO: Need to implement class MCSymbolXCOFF.
+      break;
     }
   }
   return new (Name, *this) MCSymbol(MCSymbol::SymbolKindUnset, Name,
Index: llvm/trunk/lib/MC/MCObjectFileInfo.cpp
===================================================================
--- llvm/trunk/lib/MC/MCObjectFileInfo.cpp
+++ llvm/trunk/lib/MC/MCObjectFileInfo.cpp
@@ -801,6 +801,11 @@
     Env = IsWasm;
     initWasmMCObjectFileInfo(TT);
     break;
+  case Triple::XCOFF:
+    Env = IsXCOFF;
+    // TODO: Initialize MCObjectFileInfo for XCOFF format when
+    // MCSectionXCOFF is ready.
+    break;
   case Triple::UnknownObjectFormat:
     report_fatal_error("Cannot initialize MC for unknown object file format.");
     break;
@@ -816,6 +821,7 @@
   case Triple::MachO:
   case Triple::COFF:
   case Triple::Wasm:
+  case Triple::XCOFF:
   case Triple::UnknownObjectFormat:
     report_fatal_error("Cannot get DWARF comdat section for this object file "
                        "format: not implemented.");
Index: llvm/trunk/lib/MC/MCParser/AsmParser.cpp
===================================================================
--- llvm/trunk/lib/MC/MCParser/AsmParser.cpp
+++ llvm/trunk/lib/MC/MCParser/AsmParser.cpp
@@ -710,6 +710,9 @@
   case MCObjectFileInfo::IsWasm:
     PlatformParser.reset(createWasmAsmParser());
     break;
+  case MCObjectFileInfo::IsXCOFF:
+    // TODO: Need to implement createXCOFFAsmParser for XCOFF format.
+    break;
   }
 
   PlatformParser->Initialize(*this);
Index: llvm/trunk/lib/Support/Triple.cpp
===================================================================
--- llvm/trunk/lib/Support/Triple.cpp
+++ llvm/trunk/lib/Support/Triple.cpp
@@ -534,6 +534,9 @@
 
 static Triple::ObjectFormatType parseFormat(StringRef EnvironmentName) {
   return StringSwitch<Triple::ObjectFormatType>(EnvironmentName)
+    // "xcoff" must come before "coff" because of the order-dependendent
+    // pattern matching.
+    .EndsWith("xcoff", Triple::XCOFF)
     .EndsWith("coff", Triple::COFF)
     .EndsWith("elf", Triple::ELF)
     .EndsWith("macho", Triple::MachO)
@@ -622,6 +625,7 @@
   case Triple::ELF: return "elf";
   case Triple::MachO: return "macho";
   case Triple::Wasm: return "wasm";
+  case Triple::XCOFF: return "xcoff";
   }
   llvm_unreachable("unknown object format type");
 }
@@ -686,6 +690,8 @@
   case Triple::ppc64:
     if (T.isOSDarwin())
       return Triple::MachO;
+    else if (T.isOSAIX())
+      return Triple::XCOFF;
     return Triple::ELF;
 
   case Triple::wasm32:
Index: llvm/trunk/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
===================================================================
--- llvm/trunk/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ llvm/trunk/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5594,6 +5594,9 @@
   case MCObjectFileInfo::IsWasm:
     CurrentFormat = WASM;
     break;
+  case MCObjectFileInfo::IsXCOFF:
+    llvm_unreachable("unexpected object format");
+    break;
   }
 
   if (~Prefix->SupportedFormats & CurrentFormat) {
Index: llvm/trunk/unittests/ADT/TripleTest.cpp
===================================================================
--- llvm/trunk/unittests/ADT/TripleTest.cpp
+++ llvm/trunk/unittests/ADT/TripleTest.cpp
@@ -1258,6 +1258,11 @@
   EXPECT_EQ(Triple::Wasm,
             Triple("wasm64-unknown-wasi-musl-wasm").getObjectFormat());
 
+  EXPECT_EQ(Triple::XCOFF, Triple("powerpc-ibm-aix").getObjectFormat());
+  EXPECT_EQ(Triple::XCOFF, Triple("powerpc64-ibm-aix").getObjectFormat());
+  EXPECT_EQ(Triple::XCOFF, Triple("powerpc---xcoff").getObjectFormat());
+  EXPECT_EQ(Triple::XCOFF, Triple("powerpc64---xcoff").getObjectFormat());
+
   Triple MSVCNormalized(Triple::normalize("i686-pc-windows-msvc-elf"));
   EXPECT_EQ(Triple::ELF, MSVCNormalized.getObjectFormat());
 
@@ -1276,6 +1281,9 @@
 
   T.setObjectFormat(Triple::MachO);
   EXPECT_EQ(Triple::MachO, T.getObjectFormat());
+
+  T.setObjectFormat(Triple::XCOFF);
+  EXPECT_EQ(Triple::XCOFF, T.getObjectFormat());
 }
 
 TEST(TripleTest, NormalizeWindows) {