Index: head/contrib/compiler-rt/lib/builtins/README.txt
===================================================================
--- head/contrib/compiler-rt/lib/builtins/README.txt
+++ head/contrib/compiler-rt/lib/builtins/README.txt
@@ -57,8 +57,8 @@
 si_int __popcountdi2(di_int a);  // bit population
 si_int __popcountti2(ti_int a);  // bit population
 
-uint32_t __bswapsi2(uint32_t a);   // a byteswapped, arm only
-uint64_t __bswapdi2(uint64_t a);   // a byteswapped, arm only
+uint32_t __bswapsi2(uint32_t a);   // a byteswapped, arm/mips only
+uint64_t __bswapdi2(uint64_t a);   // a byteswapped, arm/mips only
 
 // Integral arithmetic
 
Index: head/contrib/compiler-rt/lib/builtins/bswapdi2.c
===================================================================
--- head/contrib/compiler-rt/lib/builtins/bswapdi2.c
+++ head/contrib/compiler-rt/lib/builtins/bswapdi2.c
@@ -0,0 +1,28 @@
+/* ===-- bswapdi2.c - Implement __bswapdi2 ---------------------------------===
+ *
+ *               The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __bswapdi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+COMPILER_RT_ABI uint64_t
+__bswapdi2 (uint64_t u)
+{
+	return ((((u) & 0xff00000000000000ULL) >> 56)
+	    | (((u) & 0x00ff000000000000ULL) >> 40)
+	    | (((u) & 0x0000ff0000000000ULL) >> 24)
+	    | (((u) & 0x000000ff00000000ULL) >>  8)
+	    | (((u) & 0x00000000ff000000ULL) <<  8)
+	    | (((u) & 0x0000000000ff0000ULL) << 24)
+	    | (((u) & 0x000000000000ff00ULL) << 40)
+	    | (((u) & 0x00000000000000ffULL) << 56));
+}
Index: head/contrib/compiler-rt/lib/builtins/bswapsi2.c
===================================================================
--- head/contrib/compiler-rt/lib/builtins/bswapsi2.c
+++ head/contrib/compiler-rt/lib/builtins/bswapsi2.c
@@ -0,0 +1,25 @@
+/* ===-- bswapsi2.c - Implement __bswapsi2 ---------------------------------===
+ *
+ *               The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __bswapsi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+COMPILER_RT_ABI uint32_t
+__bswapsi2 (uint32_t u)
+{
+
+	return ((((u) & 0xff000000) >> 24)
+	    | (((u) & 0x00ff0000) >>  8)
+	    | (((u) & 0x0000ff00) <<  8)
+	    | (((u) & 0x000000ff) << 24));
+}
Index: head/lib/libcompiler_rt/Makefile.inc
===================================================================
--- head/lib/libcompiler_rt/Makefile.inc
+++ head/lib/libcompiler_rt/Makefile.inc
@@ -224,3 +224,10 @@
 SRCS+=		switchu8.S
 SRCS+=		sync_synchronize.S
 .endif
+
+# GCC-6.3 on mips32 requires bswap32 built-in.
+.if ${MACHINE_CPUARCH} == "mips"
+SRCS+=		bswapdi2.c
+SRCS+=		bswapsi2.c
+.endif
+