diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 41dcb5d6ca5..40ef344df18 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2016-11-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/78546
+	* simplify-rtx.c (neg_const_int): When negating most negative
+	number in mode wider than HOST_BITS_PER_WIDE_INT, use
+	simplify_const_unary_operation to produce CONST_DOUBLE or
+	CONST_WIDE_INT.
+	(simplify_plus_minus): Hanlde the case where neg_const_int
+	doesn't return a CONST_INT.
+
 2016-11-28  Markus Trippelsdorf  <markus@trippelsdorf.de>
 
 	PR target/78556
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index f6131d48130..83fb37d8535 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -56,12 +56,17 @@ static rtx simplify_unary_operation_1 (enum rtx_code, machine_mode, rtx);
 static rtx simplify_binary_operation_1 (enum rtx_code, machine_mode,
 					rtx, rtx, rtx, rtx);
 
-/* Negate a CONST_INT rtx, truncating (because a conversion from a
-   maximally negative number can overflow).  */
+/* Negate a CONST_INT rtx.  */
 static rtx
 neg_const_int (machine_mode mode, const_rtx i)
 {
-  return gen_int_mode (-(unsigned HOST_WIDE_INT) INTVAL (i), mode);
+  unsigned HOST_WIDE_INT val = -UINTVAL (i);
+  
+  if (GET_MODE_PRECISION (mode) > HOST_BITS_PER_WIDE_INT
+      && val == UINTVAL (i))
+    return simplify_const_unary_operation (NEG, mode, CONST_CAST_RTX (i),
+					   mode);
+  return gen_int_mode (val, mode);
 }
 
 /* Test whether expression, X, is an immediate constant that represents
@@ -4507,9 +4512,12 @@ simplify_plus_minus (enum rtx_code code, machine_mode mode, rtx op0,
       rtx value = ops[n_ops - 1].op;
       if (ops[n_ops - 1].neg ^ ops[n_ops - 2].neg)
 	value = neg_const_int (mode, value);
-      ops[n_ops - 2].op = plus_constant (mode, ops[n_ops - 2].op,
-					 INTVAL (value));
-      n_ops--;
+      if (CONST_INT_P (value))
+	{
+	  ops[n_ops - 2].op = plus_constant (mode, ops[n_ops - 2].op,
+					     INTVAL (value));
+	  n_ops--;
+	}
     }
 
   /* Put a non-negated operand first, if possible.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 48ccdd969bb..04a6840299d 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2016-11-28  Jakub Jelinek  <jakub@redhat.com>
 
+	PR rtl-optimization/78546
+	* gcc.dg/torture/pr78546-1.c: New test.
+	* gcc.dg/torture/pr78546-2.c: New test.
+
 	PR fortran/78298
 	* gfortran.dg/gomp/pr78298.f90: New test.
 
diff --git a/gcc/testsuite/gcc.dg/torture/pr78546-1.c b/gcc/testsuite/gcc.dg/torture/pr78546-1.c
new file mode 100644
index 00000000000..9cae5b18858
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr78546-1.c
@@ -0,0 +1,22 @@
+/* PR rtl-optimization/78546 */
+/* { dg-do run { target int128 } } */
+
+typedef unsigned __int128 u128;
+u128 b;
+
+static inline u128
+foo (u128 p1)
+{
+  p1 += ~b;
+  return -p1;
+}
+
+int
+main ()
+{
+  asm volatile ("" : : : "memory");
+  u128 x = foo (~0x7fffffffffffffffLL);
+  if (x != 0x8000000000000001ULL)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr78546-2.c b/gcc/testsuite/gcc.dg/torture/pr78546-2.c
new file mode 100644
index 00000000000..afec5b5bfc8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr78546-2.c
@@ -0,0 +1,16 @@
+/* PR rtl-optimization/78546 */
+/* { dg-do run { target int128 } } */
+
+typedef unsigned __int128 u128;
+u128 b;
+
+int
+main ()
+{
+  asm volatile ("" : : : "memory");
+  u128 x = ((u128) ~0x7fffffffffffffffLL) - b;
+  u128 y = 1 - x;
+  if (y != 0x8000000000000001ULL)
+    __builtin_abort ();
+  return 0;
+}