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
@@ -81,12 +81,11 @@
   // Set some default feature to MC layer.
   std::string FullFS = std::string(FS);
 
-  // modern-aix-as feature should be default for all non-AIX.
-  if (!TT.isOSAIX()) {
+  if (TT.isOSAIX()) {
     if (!FullFS.empty())
-      FullFS = "+modern-aix-as," + FullFS;
+      FullFS = "+aix," + FullFS;
     else
-      FullFS = "+modern-aix-as";
+      FullFS = "+aix";
   }
 
   return createPPCMCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FullFS);
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 +57,7 @@
 
 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">;
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
@@ -988,7 +988,7 @@
 def : InstAlias<"mfxer $Rx", (MFSPR8 g8rc:$Rx, 1)>;
 
 //Disable this alias on AIX for now because as does not support them.
-let Predicates = [ModernAIXAs] in {
+let Predicates = [ModernAs] in {
   def : InstAlias<"mtudscr $Rx", (MTSPR8 3, g8rc:$Rx)>;
   def : InstAlias<"mfudscr $Rx", (MFSPR8 g8rc:$Rx, 3)>;
 }
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
@@ -1121,7 +1121,8 @@
 def IsNotISA3_1 : Predicate<"!Subtarget->isISA3_1()">;
 
 // AIX assembler may not be modern enough to support some extended mne.
-def ModernAIXAs: Predicate<"Subtarget->HasModernAIXAs">, AssemblerPredicate<(all_of FeatureModernAIXAs)>;
+def ModernAs: Predicate<"!Subtarget->isAIXABI() || Subtarget->HasModernAIXAs">, 
+                 AssemblerPredicate<(any_of (not AIXOS), FeatureModernAIXAs)>;
 
 //===----------------------------------------------------------------------===//
 // PowerPC Multiclass Definitions.
@@ -4653,7 +4654,7 @@
 def : InstAlias<"mfxer $Rx", (MFSPR gprc:$Rx, 1)>;
 
 //Disable this alias on AIX for now because as does not support them.
-let Predicates = [ModernAIXAs] in {
+let Predicates = [ModernAs] in {
 def : InstAlias<"mtudscr $Rx", (MTSPR 3, gprc:$Rx)>;
 def : InstAlias<"mfudscr $Rx", (MFSPR gprc:$Rx, 3)>;
 }
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
@@ -154,6 +154,7 @@
   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
@@ -134,6 +134,7 @@
   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
@@ -190,12 +190,11 @@
       FullFS = "+invariant-function-descriptors";
   }
 
-  // modern-aix-as feature should be default for all non-AIXs.
-  if (!TT.isOSAIX()) {
+  if (TT.isOSAIX()) {
     if (!FullFS.empty())
-      FullFS = "+modern-aix-as," + FullFS;
+      FullFS = "+aix," + FullFS;
     else
-      FullFS = "+modern-aix-as";
+      FullFS = "+aix";
   }
 
   return FullFS;
diff --git a/llvm/test/MC/PowerPC/modern-aix-as.s b/llvm/test/MC/PowerPC/modern-aix-as.s
--- a/llvm/test/MC/PowerPC/modern-aix-as.s
+++ b/llvm/test/MC/PowerPC/modern-aix-as.s
@@ -1,6 +1,10 @@
 # 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: not llvm-mc -triple powerpc64le-unknown-unknown -mattr=-modern-aix-as --show-encoding %s 2>&1 | FileCheck -check-prefix=CHECK-OLD %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]