Index: llvm/include/llvm/Support/MathExtras.h
===================================================================
--- llvm/include/llvm/Support/MathExtras.h
+++ llvm/include/llvm/Support/MathExtras.h
@@ -39,6 +39,7 @@
 #endif
 
 namespace llvm {
+
 /// The behavior an operation has on an input of 0.
 enum ZeroBehavior {
   /// The returned value is undefined.
@@ -49,6 +50,41 @@
   ZB_Width
 };
 
+/// Mathematical constants.
+namespace numbers {
+/// TODO: Track C++20 std::numbners.
+constexpr double e          = 2.718281828459045, // https://oeis.org/A001113
+                 egamma     = 0.5772156649015329, // https://oeis.org/A001620
+                 ln2        = 0.6931471805599453, // https://oeis.org/A002162
+                 ln10       = 2.302585092994046, // https://oeis.org/A002392
+                 log2e      = 1.442695040888963,
+                 log10e     = 0.4342944819032518,
+                 pi         = 3.141592653589793, // https://oeis.org/A000796
+                 inv_pi     = 0.3183098861837907, // https://oeis.org/A049541
+                 sqrtpi     = 1.772453850905516, // https://oeis.org/A002161
+                 inv_sqrtpi = 0.5641895835477563, // https://oeis.org/A087197
+                 sqrt2      = 1.414213562373095, // https://oeis.org/A002193
+                 inv_sqrt2  = 0.7071067811865475,
+                 sqrt3      = 1.732050807568877, // https://oeis.org/A002194
+                 inv_sqrt3  = 0.5773502691896258,
+                 phi        = 1.618033988749895; // https://oeis.org/A001622
+constexpr float ef          = 2.718282, // https://oeis.org/A001113
+                egammaf     = 0.5772157, // https://oeis.org/A001620
+                ln2f        = 0.6931472, // https://oeis.org/A002162
+                ln10f       = 2.302585, // https://oeis.org/A002392
+                log2ef      = 1.442695,
+                log10ef     = 0.4342945,
+                pif         = 3.141593, // https://oeis.org/A000796
+                inv_pif     = 0.3183099, // https://oeis.org/A049541
+                sqrtpif     = 1.772454, // https://oeis.org/A002161
+                inv_sqrtpif = 0.5641896, // https://oeis.org/A087197
+                sqrt2f      = 1.414214, // https://oeis.org/A002193
+                inv_sqrt2f  = 0.7071068,
+                sqrt3f      = 1.732051, // https://oeis.org/A002194
+                inv_sqrt3f  = 0.5773503,
+                phif        = 1.618034; // https://oeis.org/A001622
+} // namespace numbers
+
 namespace detail {
 template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
   static unsigned count(T Val, ZeroBehavior) {
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4974,12 +4974,11 @@
     // Put the exponent in the right bit position for later addition to the
     // final result:
     //
-    //   #define LOG2OFe 1.4426950f
-    //   t0 = Op * LOG2OFe
+    // t0 = Op * log2(e)
 
     // TODO: What fast-math-flags should be set here?
     SDValue t0 = DAG.getNode(ISD::FMUL, dl, MVT::f32, Op,
-                             getF32Constant(DAG, 0x3fb8aa3b, dl));
+                             DAG.getConstantFP(numbers::log2ef, dl, MVT::f32));
     return getLimitedPrecisionExp2(t0, dl, DAG);
   }
 
@@ -4997,10 +4996,11 @@
       LimitFloatPrecision > 0 && LimitFloatPrecision <= 18) {
     SDValue Op1 = DAG.getNode(ISD::BITCAST, dl, MVT::i32, Op);
 
-    // Scale the exponent by log(2) [0.69314718f].
+    // Scale the exponent by log(2).
     SDValue Exp = GetExponent(DAG, Op1, TLI, dl);
-    SDValue LogOfExponent = DAG.getNode(ISD::FMUL, dl, MVT::f32, Exp,
-                                        getF32Constant(DAG, 0x3f317218, dl));
+    SDValue LogOfExponent =
+        DAG.getNode(ISD::FMUL, dl, MVT::f32, Exp,
+                    DAG.getConstantFP(numbers::ln2f, dl, MVT::f32));
 
     // Get the significand and build it into a floating-point number with
     // exponent of 1.
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -48,7 +48,6 @@
                          cl::desc("Enable unsafe double to float "
                                   "shrinking for math lib calls"));
 
-
 //===----------------------------------------------------------------------===//
 // Helper Functions
 //===----------------------------------------------------------------------===//
@@ -1941,9 +1940,9 @@
            ArgID == Intrinsic::exp || ArgID == Intrinsic::exp2) {
     Constant *Eul;
     if (ArgLb == ExpLb || ArgID == Intrinsic::exp)
-      // FIXME: The Euler number should be M_E, but it's place of definition
-      // is not quite standard.
-      Eul = ConstantFP::get(Log->getType(), 2.7182818284590452354);
+      // FIXME: The `long double` type is not fully supported by the classes
+      // `APFloat` and `Constant`.
+      Eul = ConstantFP::get(Log->getType(), numbers::e);
     else if (ArgLb == Exp2Lb || ArgID == Intrinsic::exp2)
       Eul = ConstantFP::get(Log->getType(), 2.0);
     else