Index: include/llvm/ADT/APInt.h
===================================================================
--- include/llvm/ADT/APInt.h
+++ include/llvm/ADT/APInt.h
@@ -510,6 +510,23 @@
     return Res;
   }
 
+  /// \brief Get a value with upper bits starting at loBit set.
+  ///
+  /// Constructs an APInt value that has a contiguous range of bits set. The
+  /// bits from loBit (inclusive) to numBits (exclusive) will be set. All other
+  /// bits will be zero. For example, with parameters(32, 12) you would get
+  /// 0xFFFFF000.
+  ///
+  /// \param numBits the intended bit width of the result
+  /// \param loBit the index of the lowest bit to set.
+  ///
+  /// \returns An APInt value with the requested bits set.
+  static APInt getBitsSetFrom(unsigned numBits, unsigned loBit) {
+    APInt Res(numBits, 0);
+    Res.setBitsFrom(loBit);
+    return Res;
+  }
+
   /// \brief Get a value with high bits set
   ///
   /// Constructs an APInt value that has the top hiBitsSet bits set.
@@ -1250,6 +1267,11 @@
     }
   }
 
+  /// Set the top bits starting from loBit.
+  void setBitsFrom(unsigned loBit) {
+    return setBits(loBit, BitWidth);
+  }
+
   /// Set the bottom loBits bits.
   void setLowBits(unsigned loBits) {
     return setBits(0, loBits);
Index: unittests/ADT/APIntTest.cpp
===================================================================
--- unittests/ADT/APIntTest.cpp
+++ unittests/ADT/APIntTest.cpp
@@ -1681,3 +1681,14 @@
   EXPECT_EQ(16u, i32hi16.countPopulation());
 
 }
+
+TEST(APIntTest, setBitsFrom) {
+  APInt i64from63(64, 0);
+  i64from63.setBitsFrom(63);
+  EXPECT_EQ(1u, i64from63.countLeadingOnes());
+  EXPECT_EQ(0u, i64from63.countLeadingZeros());
+  EXPECT_EQ(64u, i64from63.getActiveBits());
+  EXPECT_EQ(63u, i64from63.countTrailingZeros());
+  EXPECT_EQ(0u, i64from63.countTrailingOnes());
+  EXPECT_EQ(1u, i64from63.countPopulation());
+}