diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
@@ -78,7 +78,17 @@
 
 static MCSubtargetInfo *createPPCMCSubtargetInfo(const Triple &TT,
                                                  StringRef CPU, StringRef FS) {
-  return createPPCMCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
+  // Set some default feature to MC layer.
+  std::string FullFS = std::string(FS);
+
+  if (TT.isOSAIX()) {
+    if (!FullFS.empty())
+      FullFS = "+aix," + FullFS;
+    else
+      FullFS = "+aix";
+  }
+
+  return createPPCMCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FullFS);
 }
 
 static MCAsmInfo *createPPCMCAsmInfo(const MCRegisterInfo &MRI,
diff --git a/llvm/lib/Target/PowerPC/PPC.td b/llvm/lib/Target/PowerPC/PPC.td
--- a/llvm/lib/Target/PowerPC/PPC.td
+++ b/llvm/lib/Target/PowerPC/PPC.td
@@ -57,6 +57,10 @@
 
 def Feature64Bit     : SubtargetFeature<"64bit","Has64BitSupport", "true",
                                         "Enable 64-bit instructions">;
+def AIXOS: SubtargetFeature<"aix", "IsAIX", "true", "AIX OS">;
+def FeatureModernAIXAs
+    : SubtargetFeature<"modern-aix-as", "HasModernAIXAs", "true",
+                       "AIX system assembler is modern enough to support new mnes">;
 def FeatureHardFloat : SubtargetFeature<"hard-float", "HasHardFloat", "true",
                               "Enable floating-point instructions">;
 def Feature64BitRegs : SubtargetFeature<"64bitregs","Use64BitRegs", "true",
diff --git a/llvm/lib/Target/PowerPC/PPCInstr64Bit.td b/llvm/lib/Target/PowerPC/PPCInstr64Bit.td
--- a/llvm/lib/Target/PowerPC/PPCInstr64Bit.td
+++ b/llvm/lib/Target/PowerPC/PPCInstr64Bit.td
@@ -987,8 +987,11 @@
 def : InstAlias<"mtxer $Rx", (MTSPR8 1, g8rc:$Rx)>;
 def : InstAlias<"mfxer $Rx", (MFSPR8 g8rc:$Rx, 1)>;
 
-def : InstAlias<"mtudscr $Rx", (MTSPR8 3, g8rc:$Rx)>;
-def : InstAlias<"mfudscr $Rx", (MFSPR8 g8rc:$Rx, 3)>;
+//Disable this alias on AIX for now because as does not support them.
+let Predicates = [ModernAs] in {
+  def : InstAlias<"mtudscr $Rx", (MTSPR8 3, g8rc:$Rx)>;
+  def : InstAlias<"mfudscr $Rx", (MFSPR8 g8rc:$Rx, 3)>;
+}
 
 def : InstAlias<"mfrtcu $Rx", (MFSPR8 g8rc:$Rx, 4)>;
 def : InstAlias<"mfrtcl $Rx", (MFSPR8 g8rc:$Rx, 5)>;
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.td b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
@@ -1120,6 +1120,10 @@
 def PCRelativeMemops : Predicate<"Subtarget->hasPCRelativeMemops()">;
 def IsNotISA3_1 : Predicate<"!Subtarget->isISA3_1()">;
 
+// AIX assembler may not be modern enough to support some extended mne.
+def ModernAs: Predicate<"!Subtarget->isAIXABI() || Subtarget->HasModernAIXAs">, 
+                 AssemblerPredicate<(any_of (not AIXOS), FeatureModernAIXAs)>;
+
 //===----------------------------------------------------------------------===//
 // PowerPC Multiclass Definitions.
 
@@ -4649,8 +4653,11 @@
 def : InstAlias<"mtxer $Rx", (MTSPR 1, gprc:$Rx)>;
 def : InstAlias<"mfxer $Rx", (MFSPR gprc:$Rx, 1)>;
 
+//Disable this alias on AIX for now because as does not support them.
+let Predicates = [ModernAs] in {
 def : InstAlias<"mtudscr $Rx", (MTSPR 3, gprc:$Rx)>;
 def : InstAlias<"mfudscr $Rx", (MFSPR gprc:$Rx, 3)>;
+}
 
 def : InstAlias<"mfrtcu $Rx", (MFSPR gprc:$Rx, 4)>;
 def : InstAlias<"mfrtcl $Rx", (MFSPR gprc:$Rx, 5)>;
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.h b/llvm/lib/Target/PowerPC/PPCSubtarget.h
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -153,6 +153,8 @@
   bool UsePPCPostRASchedStrategy;
   bool PairedVectorMemops;
   bool PredictableSelectIsExpensive;
+  bool HasModernAIXAs;
+  bool IsAIX;
 
   POPCNTDKind HasPOPCNTD;
 
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -133,6 +133,8 @@
   UsePPCPostRASchedStrategy = false;
   PairedVectorMemops = false;
   PredictableSelectIsExpensive = false;
+  HasModernAIXAs = false;
+  IsAIX = false;
 
   HasPOPCNTD = POPCNTD_Unavailable;
 }
diff --git a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
--- a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -190,6 +190,13 @@
       FullFS = "+invariant-function-descriptors";
   }
 
+  if (TT.isOSAIX()) {
+    if (!FullFS.empty())
+      FullFS = "+aix," + FullFS;
+    else
+      FullFS = "+aix";
+  }
+
   return FullFS;
 }
 
diff --git a/llvm/test/MC/Disassembler/PowerPC/ppc64-encoding-ext.txt b/llvm/test/MC/Disassembler/PowerPC/ppc64-encoding-ext.txt
--- a/llvm/test/MC/Disassembler/PowerPC/ppc64-encoding-ext.txt
+++ b/llvm/test/MC/Disassembler/PowerPC/ppc64-encoding-ext.txt
@@ -1,4 +1,7 @@
-# RUN: llvm-mc --disassemble %s -triple powerpc64-unknown-unknown -mcpu=pwr7 | FileCheck %s
+# RUN: llvm-mc --disassemble %s -triple powerpc64-unknown-unknown -mcpu=pwr7 | FileCheck %s --check-prefixes=CHECK,MODERN
+# RUN: llvm-mc --disassemble %s -triple powerpc64-unknown-linux-gnu -mcpu=pwr7 | FileCheck %s --check-prefixes=CHECK,MODERN
+# RUN: llvm-mc --disassemble %s -triple powerpc64-ibm-aix-xcoff -mcpu=pwr7 | FileCheck %s --check-prefixes=CHECK,OLD
+# RUN: llvm-mc --disassemble %s -triple powerpc64-ibm-aix-xcoff -mattr=+modern-aix-as -mcpu=pwr7 | FileCheck %s --check-prefixes=CHECK,MODERN
 
 # FIXME: decode as beqlr 0
 # CHECK: bclr 12, 2
@@ -2212,10 +2215,12 @@
 # CHECK: mfxer 2
 0x7c 0x41 0x02 0xa6
 
-# CHECK: mtudscr 2
+# MODERN: mtudscr 2
+# OLD: mtspr 3, 2
 0x7c 0x43 0x03 0xa6
 
-# CHECK: mfudscr 2
+# MODERN: mfudscr 2
+# OLD: mfspr 2, 3
 0x7c 0x43 0x02 0xa6
 
 # CHECK: mtlr 2
diff --git a/llvm/test/MC/PowerPC/modern-aix-as.s b/llvm/test/MC/PowerPC/modern-aix-as.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/PowerPC/modern-aix-as.s
@@ -0,0 +1,16 @@
+# RUN: llvm-mc -triple powerpc64-unknown-unknown -mattr=+modern-aix-as --show-encoding %s | FileCheck -check-prefix=CHECK-BE %s
+# RUN: llvm-mc -triple powerpc64le-unknown-unknown -mattr=+modern-aix-as --show-encoding %s | FileCheck -check-prefix=CHECK-LE %s
+# RUN: llvm-mc -triple powerpc64le-unknown-unknown -mattr=-modern-aix-as --show-encoding %s | FileCheck -check-prefix=CHECK-LE %s
+# RUN: not llvm-mc -triple powerpc64le-unknown-unknown -mattr=+aix --show-encoding %s 2>&1 | FileCheck -check-prefix=CHECK-OLD %s
+##TODO: Replace above with following when implement createXCOFFAsmParser
+# UN: llvm-mc -triple powerpc-aix-ibm-xcoff -mattr=+modern-aix-as --show-encoding %s 2>&1 | FileCheck -check-prefix=CHECK-BE %s
+# UN: not llvm-mc -triple powerpc-aix-ibm-xcoff --show-encoding %s 2>&1 | FileCheck -check-prefix=CHECK-OLD %s
+
+# CHECK-BE: mtudscr 2                       # encoding: [0x7c,0x43,0x03,0xa6]
+# CHECK-LE: mtudscr 2                       # encoding: [0xa6,0x03,0x43,0x7c]
+# CHECK-OLD: instruction use requires an option to be enabled
+            mtudscr 2
+# CHECK-BE: mfudscr 2                       # encoding: [0x7c,0x43,0x02,0xa6]
+# CHECK-LE: mfudscr 2                       # encoding: [0xa6,0x02,0x43,0x7c]
+            mfudscr 2
+