Index: llvm/include/llvm/Support/MathExtras.h
===================================================================
--- llvm/include/llvm/Support/MathExtras.h
+++ llvm/include/llvm/Support/MathExtras.h
@@ -461,6 +461,16 @@
   return N >= 64 || (minIntN(N) <= x && x <= maxIntN(N));
 }
 
+/// Checks if an unsigned integer is an N bit number shifted left by S.  Dynamic
+/// version of isShiftedUInt.
+inline bool isShiftedUIntN(unsigned N, unsigned S, uint64_t x) {
+  assert(
+      N > 0 &&
+      "isShiftedUIntN(0, S, x) doesn't make sense (refers to a 0-bit number)");
+  assert(N + S <= 64 && "isShiftedUInt(N, S, x) with N + S > 64 is too wide.");
+  return isUIntN(N + S, x) && (x % (UINT64_C(1) << S) == 0);
+}
+
 /// Return true if the argument is a non-empty sequence of ones starting at the
 /// least significant bit with the remainder zero (32 bit version).
 /// Ex. isMask_32(0x0000FFFFU) == true.
Index: llvm/unittests/Support/MathExtrasTest.cpp
===================================================================
--- llvm/unittests/Support/MathExtrasTest.cpp
+++ llvm/unittests/Support/MathExtrasTest.cpp
@@ -493,6 +493,22 @@
   EXPECT_FALSE((isShiftedUInt<10, 5>(uint64_t(0x201) << 6)));
 }
 
+TEST(MathExtras, IsShiftedUIntN) {
+  EXPECT_TRUE((isShiftedUIntN(1, 0, 0)));
+  EXPECT_TRUE((isShiftedUIntN(1, 0, 1)));
+  EXPECT_FALSE((isShiftedUIntN(1, 0, 2)));
+  EXPECT_FALSE((isShiftedUIntN(1, 0, 3)));
+  EXPECT_FALSE((isShiftedUIntN(1, 0, 0x8000000000000000)));
+  EXPECT_TRUE((isShiftedUIntN(1, 63, 0x8000000000000000)));
+  EXPECT_TRUE((isShiftedUIntN(2, 62, 0xC000000000000000)));
+  EXPECT_FALSE((isShiftedUIntN(2, 62, 0xE000000000000000)));
+
+  // 0x201 is ten bits long and has a 1 in the MSB and LSB.
+  EXPECT_TRUE((isShiftedUIntN(10, 5, (uint64_t(0x201) << 5))));
+  EXPECT_FALSE((isShiftedUIntN(10, 5, (uint64_t(0x201) << 4))));
+  EXPECT_FALSE((isShiftedUIntN(10, 5, (uint64_t(0x201) << 6))));
+}
+
 TEST(MathExtras, IsShiftedInt) {
   EXPECT_TRUE((isShiftedInt<1, 0>(0)));
   EXPECT_TRUE((isShiftedInt<1, 0>(-1)));