Index: lib/Target/Mips/AsmParser/MipsAsmParser.cpp
===================================================================
--- lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -222,6 +222,7 @@
     return (STI.getFeatureBits() & Mips::FeatureFP64Bit) != 0;
   }
 
+  bool isN32() const { return STI.getFeatureBits() & Mips::FeatureN32; }
   bool isN64() const { return STI.getFeatureBits() & Mips::FeatureN64; }
 
   bool isMicroMips() const {
@@ -1035,21 +1036,23 @@
            .Case("t9", 25)
            .Default(-1);
 
-  // Although SGI documentation just cuts out t0-t3 for n32/n64,
-  // GNU pushes the values of t0-t3 to override the o32/o64 values for t4-t7
-  // We are supporting both cases, so for t0-t3 we'll just push them to t4-t7.
-  if (isMips64() && 8 <= CC && CC <= 11)
-    CC += 4;
-
-  if (CC == -1 && isMips64())
-    CC = StringSwitch<unsigned>(Name)
-             .Case("a4", 8)
-             .Case("a5", 9)
-             .Case("a6", 10)
-             .Case("a7", 11)
-             .Case("kt0", 26)
-             .Case("kt1", 27)
-             .Default(-1);
+  if (isN32() || isN64()) {
+    // Although SGI documentation just cuts out t0-t3 for n32/n64,
+    // GNU pushes the values of t0-t3 to override the o32/o64 values for t4-t7
+    // We are supporting both cases, so for t0-t3 we'll just push them to t4-t7.
+    if (8 <= CC && CC <= 11)
+      CC += 4;
+
+    if (CC == -1)
+      CC = StringSwitch<unsigned>(Name)
+               .Case("a4", 8)
+               .Case("a5", 9)
+               .Case("a6", 10)
+               .Case("a7", 11)
+               .Case("kt0", 26)
+               .Case("kt1", 27)
+               .Default(-1);
+  }
 
   warnIfAssemblerTemporary(CC);
 
Index: test/MC/Mips/mips-register-names-o32.s
===================================================================
--- test/MC/Mips/mips-register-names-o32.s
+++ test/MC/Mips/mips-register-names-o32.s
@@ -4,6 +4,7 @@
 # Second byte of addiu with $zero at rt contains the number of the source
 # register.
 
+.set noat
 addiu	$zero, $zero, 0 # CHECK: encoding: [0x24,0x00,0x00,0x00]
 addiu	$at, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
 addiu	$v0, $zero, 0   # CHECK: encoding: [0x24,0x02,0x00,0x00]
Index: test/MC/Mips/mips-register-names.s
===================================================================
--- test/MC/Mips/mips-register-names.s
+++ test/MC/Mips/mips-register-names.s
@@ -1,39 +0,0 @@
-# RUN: llvm-mc %s -triple=mips-unknown-freebsd -show-encoding | FileCheck %s
-
-# Check that the register names are mapped to their correct numbers for o32
-# Second byte of addiu with $zero at rt contains the number of the source
-# register.
-
-addiu	$zero, $zero, 0 # CHECK: encoding: [0x24,0x00,0x00,0x00]
-addiu	$at, $zero, 0   # CHECK: encoding: [0x24,0x01,0x00,0x00]
-addiu	$v0, $zero, 0   # CHECK: encoding: [0x24,0x02,0x00,0x00]
-addiu	$v1, $zero, 0   # CHECK: encoding: [0x24,0x03,0x00,0x00]
-addiu	$a0, $zero, 0   # CHECK: encoding: [0x24,0x04,0x00,0x00]
-addiu	$a1, $zero, 0   # CHECK: encoding: [0x24,0x05,0x00,0x00]
-addiu	$a2, $zero, 0   # CHECK: encoding: [0x24,0x06,0x00,0x00]
-addiu	$a3, $zero, 0   # CHECK: encoding: [0x24,0x07,0x00,0x00]
-addiu	$t0, $zero, 0   # CHECK: encoding: [0x24,0x08,0x00,0x00]
-addiu	$t1, $zero, 0   # CHECK: encoding: [0x24,0x09,0x00,0x00]
-addiu	$t2, $zero, 0   # CHECK: encoding: [0x24,0x0a,0x00,0x00]
-addiu	$t3, $zero, 0   # CHECK: encoding: [0x24,0x0b,0x00,0x00]
-addiu	$t4, $zero, 0   # CHECK: encoding: [0x24,0x0c,0x00,0x00]
-addiu	$t5, $zero, 0   # CHECK: encoding: [0x24,0x0d,0x00,0x00]
-addiu	$t6, $zero, 0   # CHECK: encoding: [0x24,0x0e,0x00,0x00]
-addiu	$t7, $zero, 0   # CHECK: encoding: [0x24,0x0f,0x00,0x00]
-addiu	$s0, $zero, 0   # CHECK: encoding: [0x24,0x10,0x00,0x00]
-addiu	$s1, $zero, 0   # CHECK: encoding: [0x24,0x11,0x00,0x00]
-addiu	$s2, $zero, 0   # CHECK: encoding: [0x24,0x12,0x00,0x00]
-addiu	$s3, $zero, 0   # CHECK: encoding: [0x24,0x13,0x00,0x00]
-addiu	$s4, $zero, 0   # CHECK: encoding: [0x24,0x14,0x00,0x00]
-addiu	$s5, $zero, 0   # CHECK: encoding: [0x24,0x15,0x00,0x00]
-addiu	$s6, $zero, 0   # CHECK: encoding: [0x24,0x16,0x00,0x00]
-addiu	$s7, $zero, 0   # CHECK: encoding: [0x24,0x17,0x00,0x00]
-addiu	$t8, $zero, 0   # CHECK: encoding: [0x24,0x18,0x00,0x00]
-addiu	$t9, $zero, 0   # CHECK: encoding: [0x24,0x19,0x00,0x00]
-addiu	$k0, $zero, 0   # CHECK: encoding: [0x24,0x1a,0x00,0x00]
-addiu	$k1, $zero, 0   # CHECK: encoding: [0x24,0x1b,0x00,0x00]
-addiu	$gp, $zero, 0   # CHECK: encoding: [0x24,0x1c,0x00,0x00]
-addiu	$sp, $zero, 0   # CHECK: encoding: [0x24,0x1d,0x00,0x00]
-addiu	$fp, $zero, 0   # CHECK: encoding: [0x24,0x1e,0x00,0x00]
-addiu	$s8, $zero, 0   # CHECK: encoding: [0x24,0x1e,0x00,0x00]
-addiu	$ra, $zero, 0   # CHECK: encoding: [0x24,0x1f,0x00,0x00]
Index: test/MC/Mips/mips64-register-names-n32-n64.s
===================================================================
--- test/MC/Mips/mips64-register-names-n32-n64.s
+++ test/MC/Mips/mips64-register-names-n32-n64.s
@@ -1,9 +1,12 @@
 # RUN: llvm-mc %s -triple=mips64-unknown-freebsd -show-encoding | FileCheck %s
+# RUN: llvm-mc %s -triple=mips64-unknown-freebsd -show-encoding \
+# RUN:     -mattr=-n64,+n32 | FileCheck %s
 
-# Check that the register names are mapped to their correct numbers for n64
+# Check that the register names are mapped to their correct numbers for n32/n64
 # Second byte of addiu with $zero at rt contains the number of the source
 # register.
 
+.set noat
 daddiu	$zero, $zero, 0 # CHECK: encoding: [0x64,0x00,0x00,0x00]
 daddiu	$at, $zero, 0   # CHECK: encoding: [0x64,0x01,0x00,0x00]
 daddiu	$v0, $zero, 0   # CHECK: encoding: [0x64,0x02,0x00,0x00]
Index: test/MC/Mips/mips64-register-names-o32.s
===================================================================
--- /dev/null
+++ test/MC/Mips/mips64-register-names-o32.s
@@ -0,0 +1,41 @@
+# RUN: llvm-mc %s -triple=mips64-unknown-freebsd -show-encoding \
+# RUN:     -mattr=-n64,+o32 | FileCheck %s
+
+# Check that the register names are mapped to their correct numbers for o32
+# Second byte of daddiu with $zero at rt contains the number of the source
+# register.
+
+.set noat
+daddiu	$zero, $zero, 0 # CHECK: encoding: [0x64,0x00,0x00,0x00]
+daddiu	$at, $zero, 0   # CHECK: encoding: [0x64,0x01,0x00,0x00]
+daddiu	$v0, $zero, 0   # CHECK: encoding: [0x64,0x02,0x00,0x00]
+daddiu	$v1, $zero, 0   # CHECK: encoding: [0x64,0x03,0x00,0x00]
+daddiu	$a0, $zero, 0   # CHECK: encoding: [0x64,0x04,0x00,0x00]
+daddiu	$a1, $zero, 0   # CHECK: encoding: [0x64,0x05,0x00,0x00]
+daddiu	$a2, $zero, 0   # CHECK: encoding: [0x64,0x06,0x00,0x00]
+daddiu	$a3, $zero, 0   # CHECK: encoding: [0x64,0x07,0x00,0x00]
+daddiu	$t0, $zero, 0   # CHECK: encoding: [0x64,0x08,0x00,0x00]
+daddiu	$t1, $zero, 0   # CHECK: encoding: [0x64,0x09,0x00,0x00]
+daddiu	$t2, $zero, 0   # CHECK: encoding: [0x64,0x0a,0x00,0x00]
+daddiu	$t3, $zero, 0   # CHECK: encoding: [0x64,0x0b,0x00,0x00]
+daddiu	$t4, $zero, 0   # CHECK: encoding: [0x64,0x0c,0x00,0x00]
+daddiu	$t5, $zero, 0   # CHECK: encoding: [0x64,0x0d,0x00,0x00]
+daddiu	$t6, $zero, 0   # CHECK: encoding: [0x64,0x0e,0x00,0x00]
+daddiu	$t7, $zero, 0   # CHECK: encoding: [0x64,0x0f,0x00,0x00]
+daddiu	$s0, $zero, 0   # CHECK: encoding: [0x64,0x10,0x00,0x00]
+daddiu	$s1, $zero, 0   # CHECK: encoding: [0x64,0x11,0x00,0x00]
+daddiu	$s2, $zero, 0   # CHECK: encoding: [0x64,0x12,0x00,0x00]
+daddiu	$s3, $zero, 0   # CHECK: encoding: [0x64,0x13,0x00,0x00]
+daddiu	$s4, $zero, 0   # CHECK: encoding: [0x64,0x14,0x00,0x00]
+daddiu	$s5, $zero, 0   # CHECK: encoding: [0x64,0x15,0x00,0x00]
+daddiu	$s6, $zero, 0   # CHECK: encoding: [0x64,0x16,0x00,0x00]
+daddiu	$s7, $zero, 0   # CHECK: encoding: [0x64,0x17,0x00,0x00]
+daddiu	$t8, $zero, 0   # CHECK: encoding: [0x64,0x18,0x00,0x00]
+daddiu	$t9, $zero, 0   # CHECK: encoding: [0x64,0x19,0x00,0x00]
+daddiu	$k0, $zero, 0   # CHECK: encoding: [0x64,0x1a,0x00,0x00]
+daddiu	$k1, $zero, 0   # CHECK: encoding: [0x64,0x1b,0x00,0x00]
+daddiu	$gp, $zero, 0   # CHECK: encoding: [0x64,0x1c,0x00,0x00]
+daddiu	$sp, $zero, 0   # CHECK: encoding: [0x64,0x1d,0x00,0x00]
+daddiu	$fp, $zero, 0   # CHECK: encoding: [0x64,0x1e,0x00,0x00]
+daddiu	$s8, $zero, 0   # CHECK: encoding: [0x64,0x1e,0x00,0x00]
+daddiu	$ra, $zero, 0   # CHECK: encoding: [0x64,0x1f,0x00,0x00]
Index: test/MC/Mips/mips64-register-names.s
===================================================================
--- test/MC/Mips/mips64-register-names.s
+++ test/MC/Mips/mips64-register-names.s
@@ -1,39 +0,0 @@
-# RUN: llvm-mc %s -triple=mips64-unknown-freebsd -show-encoding | FileCheck %s
-
-# Check that the register names are mapped to their correct numbers for n64
-# Second byte of addiu with $zero at rt contains the number of the source
-# register.
-
-daddiu	$zero, $zero, 0 # CHECK: encoding: [0x64,0x00,0x00,0x00]
-daddiu	$at, $zero, 0   # CHECK: encoding: [0x64,0x01,0x00,0x00]
-daddiu	$v0, $zero, 0   # CHECK: encoding: [0x64,0x02,0x00,0x00]
-daddiu	$v1, $zero, 0   # CHECK: encoding: [0x64,0x03,0x00,0x00]
-daddiu	$a0, $zero, 0   # CHECK: encoding: [0x64,0x04,0x00,0x00]
-daddiu	$a1, $zero, 0   # CHECK: encoding: [0x64,0x05,0x00,0x00]
-daddiu	$a2, $zero, 0   # CHECK: encoding: [0x64,0x06,0x00,0x00]
-daddiu	$a3, $zero, 0   # CHECK: encoding: [0x64,0x07,0x00,0x00]
-daddiu	$a4, $zero, 0   # CHECK: encoding: [0x64,0x08,0x00,0x00]
-daddiu	$a5, $zero, 0   # CHECK: encoding: [0x64,0x09,0x00,0x00]
-daddiu	$a6, $zero, 0   # CHECK: encoding: [0x64,0x0a,0x00,0x00]
-daddiu	$a7, $zero, 0   # CHECK: encoding: [0x64,0x0b,0x00,0x00]
-daddiu	$t4, $zero, 0   # CHECK: encoding: [0x64,0x0c,0x00,0x00]
-daddiu	$t5, $zero, 0   # CHECK: encoding: [0x64,0x0d,0x00,0x00]
-daddiu	$t6, $zero, 0   # CHECK: encoding: [0x64,0x0e,0x00,0x00]
-daddiu	$t7, $zero, 0   # CHECK: encoding: [0x64,0x0f,0x00,0x00]
-daddiu	$s0, $zero, 0   # CHECK: encoding: [0x64,0x10,0x00,0x00]
-daddiu	$s1, $zero, 0   # CHECK: encoding: [0x64,0x11,0x00,0x00]
-daddiu	$s2, $zero, 0   # CHECK: encoding: [0x64,0x12,0x00,0x00]
-daddiu	$s3, $zero, 0   # CHECK: encoding: [0x64,0x13,0x00,0x00]
-daddiu	$s4, $zero, 0   # CHECK: encoding: [0x64,0x14,0x00,0x00]
-daddiu	$s5, $zero, 0   # CHECK: encoding: [0x64,0x15,0x00,0x00]
-daddiu	$s6, $zero, 0   # CHECK: encoding: [0x64,0x16,0x00,0x00]
-daddiu	$s7, $zero, 0   # CHECK: encoding: [0x64,0x17,0x00,0x00]
-daddiu	$t8, $zero, 0   # CHECK: encoding: [0x64,0x18,0x00,0x00]
-daddiu	$t9, $zero, 0   # CHECK: encoding: [0x64,0x19,0x00,0x00]
-daddiu	$kt0, $zero, 0  # CHECK: encoding: [0x64,0x1a,0x00,0x00]
-daddiu	$kt1, $zero, 0  # CHECK: encoding: [0x64,0x1b,0x00,0x00]
-daddiu	$gp, $zero, 0   # CHECK: encoding: [0x64,0x1c,0x00,0x00]
-daddiu	$sp, $zero, 0   # CHECK: encoding: [0x64,0x1d,0x00,0x00]
-daddiu	$s8, $zero, 0   # CHECK: encoding: [0x64,0x1e,0x00,0x00]
-daddiu	$fp, $zero, 0   # CHECK: encoding: [0x64,0x1e,0x00,0x00]
-daddiu	$ra, $zero, 0   # CHECK: encoding: [0x64,0x1f,0x00,0x00]