Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -1031,6 +1031,17 @@
   getMipsCPUAndABI(Args, Triple, CPUName, ABIName);
   ABIName = getGnuCompatibleMipsABIName(ABIName);
 
+  // Always override the backend's default ABI.
+  StringRef ABIFeature = llvm::StringSwitch<StringRef>(ABIName)
+                              .Case("32", "+o32")
+                              .Case("n32", "+n32")
+                              .Case("64", "+n64")
+                              .Case("eabi", "+eabi")
+                              .Default(("+" + ABIName).str());
+  Features.push_back("-o32");
+  Features.push_back("-n64");
+  Features.push_back(Args.MakeArgString(ABIFeature));
+
   StringRef FloatABI = getMipsFloatABI(D, Args);
   if (FloatABI == "soft") {
     // FIXME: Note, this is a hack. We need to pass the selected float
Index: test/Driver/mips-integrated-as.s
===================================================================
--- /dev/null
+++ test/Driver/mips-integrated-as.s
@@ -0,0 +1,207 @@
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-O32 %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mabi=32 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-O32 %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mabi=o32 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-O32 %s
+// ABI-O32: -cc1as
+// ABI-O32: "-target-feature" "-n64"
+// ABI-O32: "-target-feature" "+o32"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mabi=eabi 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-EABI32 %s
+// ABI-EABI32: -cc1as
+// ABI-EABI32: "-target-feature" "-o32"
+// ABI-EABI32: "-target-feature" "-n64"
+// ABI-EABI32: "-target-feature" "+eabi"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips64 -mabi=n32 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N32 %s
+// RUN: %clang -target mips64-linux-gnu -### -fintegrated-as -c %s -mabi=n32 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N32 %s
+// ABI-N32: -cc1as
+// ABI-N32: "-target-feature" "-o32"
+// ABI-N32: "-target-feature" "-n64"
+// ABI-N32: "-target-feature" "+n32"
+
+// FIXME: We should also test '-target mips-linux-gnu -mips64' defaults to the
+//        default 64-bit ABI (N64 but GCC uses N32). It currently selects O32
+//        because of the triple.
+// RUN: %clang -target mips64-linux-gnu -### -fintegrated-as -c %s -mips64 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N64 %s
+//
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips64 -mabi=64 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N64 %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips64 -mabi=n64 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N64 %s
+// RUN: %clang -target mips64-linux-gnu -### -fintegrated-as -c %s -mips64 -mabi=64 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N64 %s
+// RUN: %clang -target mips64-linux-gnu -### -fintegrated-as -c %s -mips64 -mabi=n64 2>&1 | \
+// RUN:   FileCheck -check-prefix=ABI-N64 %s
+// ABI-N64: -cc1as
+// ABI-N64: "-target-feature" "-o32"
+// ABI-N64: "-target-feature" "+n64"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -msoft-float 2>&1 | \
+// RUN:   FileCheck -check-prefix=SOFTFLOAT %s
+// SOFTFLOAT: -cc1as
+// SOFTFLOAT: "-target-feature" "+soft-float"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=HARDFLOAT %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mhard-float 2>&1 | \
+// RUN:   FileCheck -check-prefix=HARDFLOAT %s
+// HARDFLOAT: -cc1as
+// HARDFLOAT-NOT: "-target-feature" "+soft-float"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=NAN-DEFAULT %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips32r6 2>&1 | \
+// RUN:   FileCheck -check-prefix=NAN-DEFAULT %s
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips64r6 2>&1 | \
+// RUN:   FileCheck -check-prefix=NAN-DEFAULT %s
+// NAN-DEFAULT: -cc1as
+// NAN-DEFAULT-NOT: "-target-feature" "{{[-+]}}nan2008"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mnan=legacy 2>&1 | \
+// RUN:   FileCheck -check-prefix=NAN-LEGACY %s
+// NAN-LEGACY: -cc1as
+// NAN-LEGACY: "-target-feature" "-nan2008"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mnan=2008 2>&1 | \
+// RUN:   FileCheck -check-prefix=NAN-2008 %s
+// NAN-2008: -cc1as
+// NAN-2008: "-target-feature" "+nan2008"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=DEFAULT-FLOAT %s
+// DEFAULT-FLOAT: -cc1as
+// DEFAULT-FLOAT-NOT: "-target-feature" "{{[+-]}}single-float"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -msingle-float 2>&1 | \
+// RUN:   FileCheck -check-prefix=SINGLE-FLOAT %s
+// SINGLE-FLOAT: -cc1as
+// SINGLE-FLOAT: "-target-feature" "+single-float"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mdouble-float 2>&1 | \
+// RUN:   FileCheck -check-prefix=DOUBLE-FLOAT %s
+// DOUBLE-FLOAT: -cc1as
+// DOUBLE-FLOAT: "-target-feature" "-single-float"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=MIPS16-DEFAULT %s
+// MIPS16-DEFAULT: -cc1as
+// MIPS16-DEFAULT-NOT: "-target-feature" "{{[+-]}}mips16"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mips16 2>&1 | \
+// RUN:   FileCheck -check-prefix=MIPS16-ON %s
+// MIPS16-ON: -cc1as
+// MIPS16-ON: "-target-feature" "+mips16"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-mips16 2>&1 | \
+// RUN:   FileCheck -check-prefix=MIPS16-OFF %s
+// MIPS16-OFF: -cc1as
+// MIPS16-OFF: "-target-feature" "-mips16"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=MICROMIPS-DEFAULT %s
+// MICROMIPS-DEFAULT: -cc1as
+// MICROMIPS-DEFAULT-NOT: "-target-feature" "{{[+-]}}micromips"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mmicromips 2>&1 | \
+// RUN:   FileCheck -check-prefix=MICROMIPS-ON %s
+// MICROMIPS-ON: -cc1as
+// MICROMIPS-ON: "-target-feature" "+micromips"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-micromips 2>&1 | \
+// RUN:   FileCheck -check-prefix=MICROMIPS-OFF %s
+// MICROMIPS-OFF: -cc1as
+// MICROMIPS-OFF: "-target-feature" "-micromips"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSP-DEFAULT %s
+// DSP-DEFAULT: -cc1as
+// DSP-DEFAULT-NOT: "-target-feature" "{{[+-]}}dsp"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mdsp 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSP-ON %s
+// DSP-ON: -cc1as
+// DSP-ON: "-target-feature" "+dsp"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-dsp 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSP-OFF %s
+// DSP-OFF: -cc1as
+// DSP-OFF: "-target-feature" "-dsp"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSPR2-DEFAULT %s
+// DSPR2-DEFAULT: -cc1as
+// DSPR2-DEFAULT-NOT: "-target-feature" "{{[+-]}}dspr2"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mdspr2 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSPR2-ON %s
+// DSPR2-ON: -cc1as
+// DSPR2-ON: "-target-feature" "+dspr2"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-dspr2 2>&1 | \
+// RUN:   FileCheck -check-prefix=DSPR2-OFF %s
+// DSPR2-OFF: -cc1as
+// DSPR2-OFF: "-target-feature" "-dspr2"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=MSA-DEFAULT %s
+// MSA-DEFAULT: -cc1as
+// MSA-DEFAULT-NOT: "-target-feature" "{{[+-]}}msa"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mmsa 2>&1 | \
+// RUN:   FileCheck -check-prefix=MSA-ON %s
+// MSA-ON: -cc1as
+// MSA-ON: "-target-feature" "+msa"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-msa 2>&1 | \
+// RUN:   FileCheck -check-prefix=MSA-OFF %s
+// MSA-OFF: -cc1as
+// MSA-OFF: "-target-feature" "-msa"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=FPXX-DEFAULT %s
+// FPXX-DEFAULT: -cc1as
+// FPXX-DEFAULT-NOT: "-target-feature" "+fpxx"
+// FPXX-DEFAULT-NOT: "-target-feature" "+nooddspreg"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mfp32 2>&1 | \
+// RUN:   FileCheck -check-prefix=FP32 %s
+// FP32: -cc1as
+// FP32: "-target-feature" "-fp64"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mfpxx 2>&1 | \
+// RUN:   FileCheck -check-prefix=FPXX %s
+// FPXX: -cc1as
+// FPXX: "-target-feature" "+fpxx"
+// FPXX: "-target-feature" "+nooddspreg"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mfp64 2>&1 | \
+// RUN:   FileCheck -check-prefix=FP64 %s
+// FP64: -cc1as
+// FP64: "-target-feature" "+fp64"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=ODDSPREG-DEFAULT %s
+// ODDSPREG-DEFAULT: -cc1as
+// ODDSPREG-DEFAULT-NOT: "-target-feature" "{{[+-]}}nooddspreg"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -modd-spreg 2>&1 | \
+// RUN:   FileCheck -check-prefix=ODDSPREG-ON %s
+// ODDSPREG-ON: -cc1as
+// ODDSPREG-ON: "-target-feature" "-nooddspreg"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mno-odd-spreg 2>&1 | \
+// RUN:   FileCheck -check-prefix=ODDSPREG-OFF %s
+// ODDSPREG-OFF: -cc1as
+// ODDSPREG-OFF: "-target-feature" "+nooddspreg"
+
+// RUN: %clang -target mips-linux-gnu -### -fintegrated-as -c %s -mfpxx -modd-spreg 2>&1 | \
+// RUN:   FileCheck -check-prefix=FPXX-ODDSPREG %s
+// FPXX-ODDSPREG: -cc1as
+// FPXX-ODDSPREG: "-target-feature" "+fpxx"
+// FPXX-ODDSPREG: "-target-feature" "-nooddspreg"