Index: lib/ubsan/ubsan_value.cc
===================================================================
--- lib/ubsan/ubsan_value.cc
+++ lib/ubsan/ubsan_value.cc
@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <endian.h>
 #include "ubsan_platform.h"
 #if CAN_SANITIZE_UB
 #include "ubsan_value.h"
@@ -27,7 +28,24 @@
     // to SIntMax.
     const unsigned ExtraBits =
       sizeof(SIntMax) * 8 - getType().getIntegerBitWidth();
+#if defined(__mips__)
+    UIntMax Value = UIntMax(Val) << ExtraBits >> ExtraBits;;
+    uptr ExtraBytes= ExtraBits / 8;
+#if BYTE_ORDER == LITTLE_ENDIAN
+    u8 * ValuePtr = (u8 *) &Value + (sizeof(UIntMax) - ExtraBytes);
+#else
+    u8 * ValuePtr = (u8 *) &Value;
+#endif
+    uptr Mask = 1UL << (getType().getIntegerBitWidth() - 1);
+    if(Val & Mask) {
+      for (uptr i = 0 ; i < ExtraBytes ; i++) {
+        *(ValuePtr + i) |= 0xff;
+      }
+    }
+    return SIntMax(Value);
+#else
     return SIntMax(Val) << ExtraBits >> ExtraBits;
+#endif
   }
   if (getType().getIntegerBitWidth() == 64)
     return *reinterpret_cast<s64*>(Val);