[builtins] Introduce proper Float64Log1p operator.

test/cctest/compiler/test-run-machops.cc

Index: test/cctest/compiler/test-run-machops.cc
diff --git a/test/cctest/compiler/test-run-machops.cc b/test/cctest/compiler/test-run-machops.cc
index 8f3efb5777ed6a6683abd6155a37baf0689692bd..b1b01a48f82e7e0ca7f418fc007e0f0d150662ba 100644
--- a/test/cctest/compiler/test-run-machops.cc
+++ b/test/cctest/compiler/test-run-machops.cc
@@ -5511,6 +5511,20 @@ TEST(RunFloat64Log) {
   FOR_FLOAT64_INPUTS(i) { CHECK_DOUBLE_EQ(ieee754::log(*i), m.Call(*i)); }
 }
 
+TEST(RunFloat64Log1p) {
+  BufferedRawMachineAssemblerTester<double> m(MachineType::Float64());
+  m.Return(m.Float64Log1p(m.Parameter(0)));
+  CHECK(std::isnan(m.Call(std::numeric_limits<double>::quiet_NaN())));
+  CHECK(std::isnan(m.Call(std::numeric_limits<double>::signaling_NaN())));
+  CHECK(std::isnan(m.Call(-std::numeric_limits<double>::infinity())));
+  CHECK_DOUBLE_EQ(-std::numeric_limits<double>::infinity(), m.Call(-1.0));
+  CHECK_DOUBLE_EQ(0.0, m.Call(0.0));
+  CHECK_DOUBLE_EQ(-0.0, m.Call(-0.0));
+  CHECK_DOUBLE_EQ(std::numeric_limits<double>::infinity(),
+                  m.Call(std::numeric_limits<double>::infinity()));
+  FOR_FLOAT64_INPUTS(i) { CHECK_DOUBLE_EQ(ieee754::log1p(*i), m.Call(*i)); }
+}
+
 static double two_30 = 1 << 30;             // 2^30 is a smi boundary.
 static double two_52 = two_30 * (1 << 22);  // 2^52 is a precision boundary.
 static double kValues[] = {0.1,