Index: llvm/include/llvm/ADT/APInt.h
===================================================================
--- llvm/include/llvm/ADT/APInt.h
+++ llvm/include/llvm/ADT/APInt.h
@@ -595,8 +595,8 @@
   /// Constructs an APInt value that has a contiguous range of bits set. The
   /// bits from loBit (inclusive) to hiBit (exclusive) will be set. All other
   /// bits will be zero. For example, with parameters(32, 0, 16) you would get
-  /// 0x0000FFFF. If hiBit is less than loBit then the set bits "wrap". For
-  /// example, with parameters (32, 28, 4), you would get 0xF000000F.
+  /// 0x0000FFFF. Please call getBitsSetWithWrap if \p loBit may be greater than
+  /// \p hiBit.
   ///
   /// \param numBits the intended bit width of the result
   /// \param loBit the index of the lowest bit set.
@@ -604,11 +604,23 @@
   ///
   /// \returns An APInt value with the requested bits set.
   static APInt getBitsSet(unsigned numBits, unsigned loBit, unsigned hiBit) {
+    assert(loBit <= hiBit && "loBit greater than hiBit");
     APInt Res(numBits, 0);
     Res.setBits(loBit, hiBit);
     return Res;
   }
 
+  /// Wrap version of getBitsSet.
+  /// If \p hiBit is no less than \p loBit, this is same with getBitsSet.
+  /// If \p hiBit is less than \p loBit, the set bits "wrap". For example, with
+  /// parameters (32, 28, 4), you would get 0xF000000F.
+  static APInt getBitsSetWithWrap(unsigned numBits, unsigned loBit,
+                                  unsigned hiBit) {
+    APInt Res(numBits, 0);
+    Res.setBitsWithWrap(loBit, hiBit);
+    return Res;
+  }
+
   /// Get a value with upper bits starting at loBit set.
   ///
   /// Constructs an APInt value that has a contiguous range of bits set. The
@@ -1431,6 +1443,21 @@
   }
 
   /// Set the bits from loBit (inclusive) to hiBit (exclusive) to 1.
+  /// This function handles "wrap" case when \p loBit > \p hiBit, and calls
+  /// setBits when \p loBit <= \p hiBit.
+  void setBitsWithWrap(unsigned loBit, unsigned hiBit) {
+    assert(hiBit <= BitWidth && "hiBit out of range");
+    assert(loBit <= BitWidth && "loBit out of range");
+    if (loBit <= hiBit) {
+      setBits(loBit, hiBit);
+      return;
+    }
+    setLowBits(hiBit);
+    setHighBits(BitWidth - loBit);
+  }
+
+  /// Set the bits from loBit (inclusive) to hiBit (exclusive) to 1.
+  /// This function handles case when \p loBit <= \p hiBit.
   void setBits(unsigned loBit, unsigned hiBit) {
     assert(hiBit <= BitWidth && "hiBit out of range");
     assert(loBit <= BitWidth && "loBit out of range");
Index: llvm/unittests/ADT/APIntTest.cpp
===================================================================
--- llvm/unittests/ADT/APIntTest.cpp
+++ llvm/unittests/ADT/APIntTest.cpp
@@ -2046,6 +2046,40 @@
   EXPECT_EQ(125u, i127hi1lo1.countPopulation());
 }
 
+TEST(APIntTest, getBitsSetWithWrap) {
+  APInt i64hi1lo1 = APInt::getBitsSetWithWrap(64, 1, 63);
+  EXPECT_EQ(0u, i64hi1lo1.countLeadingOnes());
+  EXPECT_EQ(1u, i64hi1lo1.countLeadingZeros());
+  EXPECT_EQ(63u, i64hi1lo1.getActiveBits());
+  EXPECT_EQ(1u, i64hi1lo1.countTrailingZeros());
+  EXPECT_EQ(0u, i64hi1lo1.countTrailingOnes());
+  EXPECT_EQ(62u, i64hi1lo1.countPopulation());
+
+  APInt i127hi1lo1 = APInt::getBitsSetWithWrap(127, 1, 126);
+  EXPECT_EQ(0u, i127hi1lo1.countLeadingOnes());
+  EXPECT_EQ(1u, i127hi1lo1.countLeadingZeros());
+  EXPECT_EQ(126u, i127hi1lo1.getActiveBits());
+  EXPECT_EQ(1u, i127hi1lo1.countTrailingZeros());
+  EXPECT_EQ(0u, i127hi1lo1.countTrailingOnes());
+  EXPECT_EQ(125u, i127hi1lo1.countPopulation());
+
+  APInt i64hi1lo1wrap = APInt::getBitsSetWithWrap(64, 63, 1);
+  EXPECT_EQ(1u, i64hi1lo1wrap.countLeadingOnes());
+  EXPECT_EQ(0u, i64hi1lo1wrap.countLeadingZeros());
+  EXPECT_EQ(64u, i64hi1lo1wrap.getActiveBits());
+  EXPECT_EQ(0u, i64hi1lo1wrap.countTrailingZeros());
+  EXPECT_EQ(1u, i64hi1lo1wrap.countTrailingOnes());
+  EXPECT_EQ(2u, i64hi1lo1wrap.countPopulation());
+
+  APInt i127hi1lo1wrap = APInt::getBitsSetWithWrap(127, 126, 1);
+  EXPECT_EQ(1u, i127hi1lo1wrap.countLeadingOnes());
+  EXPECT_EQ(0u, i127hi1lo1wrap.countLeadingZeros());
+  EXPECT_EQ(127u, i127hi1lo1wrap.getActiveBits());
+  EXPECT_EQ(0u, i127hi1lo1wrap.countTrailingZeros());
+  EXPECT_EQ(1u, i127hi1lo1wrap.countTrailingOnes());
+  EXPECT_EQ(2u, i127hi1lo1wrap.countPopulation());
+}
+
 TEST(APIntTest, getHighBitsSet) {
   APInt i64hi32 = APInt::getHighBitsSet(64, 32);
   EXPECT_EQ(32u, i64hi32.countLeadingOnes());