Index: llvm/include/llvm/ADT/APInt.h
===================================================================
--- llvm/include/llvm/ADT/APInt.h
+++ llvm/include/llvm/ADT/APInt.h
@@ -1417,9 +1417,13 @@
   void setBits(unsigned loBit, unsigned hiBit) {
     assert(hiBit <= BitWidth && "hiBit out of range");
     assert(loBit <= BitWidth && "loBit out of range");
-    assert(loBit <= hiBit && "loBit greater than hiBit");
     if (loBit == hiBit)
       return;
+    if (loBit > hiBit) {
+      setLowBits(hiBit);
+      setHighBits(BitWidth - loBit);
+      return;
+    }
     if (loBit < APINT_BITS_PER_WORD && hiBit <= APINT_BITS_PER_WORD) {
       uint64_t mask = WORDTYPE_MAX >> (APINT_BITS_PER_WORD - (hiBit - loBit));
       mask <<= loBit;
Index: llvm/unittests/ADT/APIntTest.cpp
===================================================================
--- llvm/unittests/ADT/APIntTest.cpp
+++ llvm/unittests/ADT/APIntTest.cpp
@@ -1907,6 +1907,22 @@
   EXPECT_EQ(1u, i127hi1lo1.countTrailingZeros());
   EXPECT_EQ(0u, i127hi1lo1.countTrailingOnes());
   EXPECT_EQ(125u, i127hi1lo1.countPopulation());
+
+  APInt i64hi1lo1wrap = APInt::getBitsSet(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::getBitsSet(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) {