diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index 2678223..684e36f 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -32,6 +32,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimplify.h"
 #include "builtins.h"
 #include "tree-inline.h"
+#include "ubsan.h"
 
 static bool verify_constant (tree, bool, bool *, bool *);
 #define VERIFY_CONSTANT(X)						\
@@ -1151,6 +1152,16 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
   constexpr_call *entry;
   bool depth_ok;
 
+  if (fun == NULL_TREE)
+    switch (CALL_EXPR_IFN (t))
+      {
+      case IFN_UBSAN_NULL:
+      case IFN_UBSAN_BOUNDS:
+	return void_node;
+      default:
+	break;
+      }
+
   if (TREE_CODE (fun) != FUNCTION_DECL)
     {
       /* Might be a constexpr function pointer.  */
@@ -1171,6 +1182,10 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
     }
   if (DECL_CLONED_FUNCTION_P (fun))
     fun = DECL_CLONED_FUNCTION (fun);
+
+  if (!current_function_decl && is_ubsan_builtin_p (fun))
+    return void_node;
+
   if (is_builtin_fn (fun))
     return cxx_eval_builtin_function_call (ctx, t,
 					   addr, non_constant_p, overflow_p);
diff --git gcc/cp/error.c gcc/cp/error.c
index 76f86cb..09789ad 100644
--- gcc/cp/error.c
+++ gcc/cp/error.c
@@ -33,6 +33,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-pretty-print.h"
 #include "c-family/c-objc.h"
 #include "ubsan.h"
+#include "internal-fn.h"
 
 #include <new>                    // For placement-new.
 
@@ -2037,6 +2038,14 @@ dump_expr (cxx_pretty_printer *pp, tree t, int flags)
 	tree fn = CALL_EXPR_FN (t);
 	bool skipfirst = false;
 
+	/* Deal with internal functions.  */
+	if (fn == NULL_TREE)
+	  {
+	    pp_string (pp, internal_fn_name (CALL_EXPR_IFN (t)));
+	    dump_call_expr_args (pp, t, flags, skipfirst);
+	    break;
+	  }
+
 	if (TREE_CODE (fn) == ADDR_EXPR)
 	  fn = TREE_OPERAND (fn, 0);
 
diff --git gcc/testsuite/g++.dg/ubsan/pr63956.C gcc/testsuite/g++.dg/ubsan/pr63956.C
index e69de29..7bc0b77 100644
--- gcc/testsuite/g++.dg/ubsan/pr63956.C
+++ gcc/testsuite/g++.dg/ubsan/pr63956.C
@@ -0,0 +1,172 @@
+// PR sanitizer/63956
+// { dg-do compile }
+// { dg-options "-std=c++14 -fsanitize=undefined,float-divide-by-zero,float-cast-overflow" }
+
+#define SA(X) static_assert((X),#X)
+#define INT_MIN (-__INT_MAX__ - 1)
+
+constexpr int
+fn1 (int a, int b)
+{
+  if (b != 2)
+    a <<= b;
+  return a;
+}
+
+constexpr int i1 = fn1 (5, 3);
+constexpr int i2 = fn1 (5, -2);
+constexpr int i3 = fn1 (5, sizeof (int) * __CHAR_BIT__);
+constexpr int i4 = fn1 (5, 256);
+constexpr int i5 = fn1 (5, 2);
+constexpr int i6 = fn1 (-2, 4);
+constexpr int i7 = fn1 (0, 2);
+
+SA (i1 == 40);
+SA (i5 == 5);
+SA (i7 == 0);
+
+constexpr int
+fn2 (int a, int b)
+{
+  if (b != 2)
+    a >>= b;
+  return a;
+}
+
+constexpr int j1 = fn2 (4, 1);
+constexpr int j2 = fn2 (4, -1);
+constexpr int j3 = fn2 (10, sizeof (int) * __CHAR_BIT__);
+constexpr int j4 = fn2 (1, 256);
+constexpr int j5 = fn2 (5, 2);
+constexpr int j6 = fn2 (-2, 4);
+constexpr int j7 = fn2 (0, 4);
+
+SA (j1 == 2);
+SA (j5 == 5);
+SA (j7 == 0);
+
+constexpr int
+fn3 (int a, int b)
+{
+  if (b != 2)
+    a = a / b;
+  return a;
+}
+
+constexpr int k1 = fn3 (8, 4);
+constexpr int k2 = fn3 (7, 0); // { dg-error "is not a constant expression|constexpr call flows off" }
+constexpr int k3 = fn3 (INT_MIN, -1); // { dg-error "overflow in constant expression|constexpr call flows off" }
+
+SA (k1 == 2);
+
+constexpr float
+fn4 (float a, float b)
+{
+  if (b != 2.0)
+    a = a / b;
+  return a;
+}
+
+constexpr float l1 = fn4 (5.0, 3.0);
+constexpr float l2 = fn4 (7.0, 0.0); // { dg-error "is not a constant expression|constexpr call flows off" }
+
+constexpr int
+fn5 (const int *a, int b)
+{
+  if (b != 2)
+    b = a[b];
+  return b;
+}
+
+constexpr int m1[4] = { 1, 2, 3, 4 };
+constexpr int m2 = fn5 (m1, 3);
+constexpr int m3 = fn5 (m1, 4); // { dg-error "array subscript out of bound|constexpr call flows off" }
+
+constexpr int
+fn6 (const int &a, int b)
+{
+  if (b != 2)
+    b = a;
+  return b;
+}
+
+constexpr int
+fn7 (const int *a, int b)
+{
+  if (b != 3)
+    return fn6 (*a, b);
+  return 7;
+}
+
+constexpr int n1 = 7;
+constexpr int n2 = fn7 (&n1, 5);
+constexpr int n3 = fn7 ((const int *) 0, 8); // { dg-error "is not a constant expression|constexpr call flows off" }
+
+constexpr int
+fn8 (int i)
+{
+  constexpr int g[10] = { };
+  return g[i];
+}
+
+constexpr int o1 = fn8 (9);
+constexpr int o2 = fn8 (10); // { dg-error "array subscript out of bound" }
+
+constexpr int
+fn9 (int a, int b)
+{
+  if (b != 0)
+    return a + b;
+  return a;
+}
+
+constexpr int p1 = fn9 (42, 7);
+constexpr int p2 = fn9 (__INT_MAX__, 1); // { dg-error "overflow in constant expression" }
+constexpr int p3 = fn9 (__INT_MAX__, -1);
+constexpr int p4 = fn9 (INT_MIN, 1);
+constexpr int p5 = fn9 (INT_MIN, -1); // { dg-error "overflow in constant expression" }
+
+SA (p1 == 49);
+SA (p3 == __INT_MAX__ - 1);
+SA (p4 == INT_MIN + 1);
+
+constexpr int
+fn10 (int a, int b)
+{
+  if (b != 0)
+    return a * b;
+  return a;
+}
+
+constexpr int q1 = fn10 (10, 10);
+constexpr int q2 = fn10 (__INT_MAX__, 2); // { dg-error "overflow in constant expression" }
+constexpr int q3 = fn10 (INT_MIN, 2); // { dg-error "overflow in constant expression" }
+constexpr int q4 = fn10 (-1, -1);
+
+SA (q1 == 100);
+SA (q4 == 1);
+
+constexpr int
+fn11 (double d)
+{
+  int i = d;
+  if (i != 0)
+    return i;
+  return i * 2;
+}
+
+constexpr int r1 = fn11 (3.4);
+constexpr int r2 = fn11 (__builtin_inf ()); // { dg-error "overflow in constant expression|constexpr call flows off" }
+
+constexpr int
+fn12 (int i)
+{
+  if (i == 42)
+    __builtin_unreachable (); // { dg-error "is not a constant expression" }
+  return i + 10;
+}
+
+constexpr int s1 = fn12 (1);
+constexpr int s2 = fn12 (42); // { dg-error "constexpr call flows off the end of the function" }
+
+SA (s1 == 11);
