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 +57,8 @@
 
 def Feature64Bit     : SubtargetFeature<"64bit","Has64BitSupport", "true",
                                         "Enable 64-bit instructions">;
+def FeatureModernAs     : SubtargetFeature<"modern-as","HasModernAs", "true",
+                                        "Has new Assembler" >;
 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 for now because as on AIX 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
@@ -1119,6 +1119,7 @@
 def HasFPU : Predicate<"Subtarget->hasFPU()">;
 def PCRelativeMemops : Predicate<"Subtarget->hasPCRelativeMemops()">;
 def IsNotISA3_1 : Predicate<"!Subtarget->isISA3_1()">;
+def ModernAs: Predicate<"Subtarget->HasModernAs">, AssemblerPredicate<(all_of FeatureModernAs)>;
 
 //===----------------------------------------------------------------------===//
 // PowerPC Multiclass Definitions.
@@ -4649,8 +4650,10 @@
 def : InstAlias<"mtxer $Rx", (MTSPR 1, gprc:$Rx)>;
 def : InstAlias<"mfxer $Rx", (MFSPR gprc:$Rx, 1)>;
 
+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 +153,7 @@
   bool UsePPCPostRASchedStrategy;
   bool PairedVectorMemops;
   bool PredictableSelectIsExpensive;
+  bool HasModernAs;
 
   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 +133,7 @@
   UsePPCPostRASchedStrategy = false;
   PairedVectorMemops = false;
   PredictableSelectIsExpensive = false;
+  HasModernAs = 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 = "+modern-as," + FullFS;
+    else
+      FullFS = "+modern-as";
+  }
+
   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 +1,5 @@
 # RUN: llvm-mc --disassemble %s -triple powerpc64-unknown-unknown -mcpu=pwr7 | FileCheck %s
+# RUN: llvm-mc --disassemble %s -triple powerpc64-unknown-unknown -mattr=+modern-as -mcpu=pwr7 | FileCheck %s --check-prefix=MODERN
 
 # FIXME: decode as beqlr 0
 # CHECK: bclr 12, 2
@@ -2212,10 +2213,12 @@
 # CHECK: mfxer 2
 0x7c 0x41 0x02 0xa6
 
-# CHECK: mtudscr 2
+# MODERN: mtudscr 2
+# CHECK: mtspr 3, 2
 0x7c 0x43 0x03 0xa6
 
-# CHECK: mfudscr 2
+# MODERN: mfudscr 2
+# CHECK: mfspr 2, 3
 0x7c 0x43 0x02 0xa6
 
 # CHECK: mtlr 2
diff --git a/llvm/test/MC/PowerPC/modern-as.s b/llvm/test/MC/PowerPC/modern-as.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/PowerPC/modern-as.s
@@ -0,0 +1,10 @@
+# RUN: llvm-mc -triple powerpc64-unknown-unknown -mattr=+modern-as --show-encoding %s | FileCheck -check-prefix=CHECK-BE %s
+# RUN: llvm-mc -triple powerpc64le-unknown-unknown -mattr=+modern-as --show-encoding %s | FileCheck -check-prefix=CHECK-LE %s
+
+# CHECK-BE: mtudscr 2                       # encoding: [0x7c,0x43,0x03,0xa6]
+# CHECK-LE: mtudscr 2                       # encoding: [0xa6,0x03,0x43,0x7c]
+            mtudscr 2
+# CHECK-BE: mfudscr 2                       # encoding: [0x7c,0x43,0x02,0xa6]
+# CHECK-LE: mfudscr 2                       # encoding: [0xa6,0x02,0x43,0x7c]
+            mfudscr 2
+
diff --git a/llvm/test/MC/PowerPC/ppc64-encoding-ext.s b/llvm/test/MC/PowerPC/ppc64-encoding-ext.s
--- a/llvm/test/MC/PowerPC/ppc64-encoding-ext.s
+++ b/llvm/test/MC/PowerPC/ppc64-encoding-ext.s
@@ -3419,12 +3419,6 @@
 # CHECK-BE: mfxer 2                         # encoding: [0x7c,0x41,0x02,0xa6]
 # CHECK-LE: mfxer 2                         # encoding: [0xa6,0x02,0x41,0x7c]
             mfxer 2
-# CHECK-BE: mtudscr 2                       # encoding: [0x7c,0x43,0x03,0xa6]
-# CHECK-LE: mtudscr 2                       # encoding: [0xa6,0x03,0x43,0x7c]
-            mtudscr 2
-# CHECK-BE: mfudscr 2                       # encoding: [0x7c,0x43,0x02,0xa6]
-# CHECK-LE: mfudscr 2                       # encoding: [0xa6,0x02,0x43,0x7c]
-            mfudscr 2
 # CHECK-BE: mfrtcu 2                        # encoding: [0x7c,0x44,0x02,0xa6]
 # CHECK-LE: mfrtcu 2                        # encoding: [0xa6,0x02,0x44,0x7c]
             mfrtcu 2