Index: lib/ubsan/ubsan_value.cc
===================================================================
--- lib/ubsan/ubsan_value.cc
+++ lib/ubsan/ubsan_value.cc
@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <stdlib.h>
 #include "ubsan_platform.h"
 #if CAN_SANITIZE_UB
 #include "ubsan_value.h"
@@ -27,7 +28,16 @@
     // to SIntMax.
     const unsigned ExtraBits =
       sizeof(SIntMax) * 8 - getType().getIntegerBitWidth();
-    return SIntMax(Val) << ExtraBits >> ExtraBits;
+    UIntMax Value;
+    if(getType().getIntegerBitWidth() == 32)
+      Value = UIntMax(abs(Val));
+    else
+      Value = UIntMax(llabs(Val));
+    Value = Value << ExtraBits >> ExtraBits;
+    uptr Mask = 1UL << (getType().getIntegerBitWidth() - 1);
+    if(Mask & Val)
+      return -(SIntMax(Value));
+    return SIntMax(Value);
   }
   if (getType().getIntegerBitWidth() == 64)
     return *reinterpret_cast<s64*>(Val);