[builtins] Migrate Math.log to TurboFan.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 07817fe8c0899444decbddebeb73acd90d6a5e6c..80fca71b2d7c884ed3b3672a369bca692ae174dc 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -2464,6 +2464,18 @@ BUILTIN(MathImul) {
   return *isolate->factory()->NewNumberFromInt(product);
 }
 
+// ES6 section 20.2.2.20 Math.log ( x )
+void Builtins::Generate_MathLog(CodeStubAssembler* assembler) {
+  using compiler::Node;
+
+  Node* x = assembler->Parameter(1);
+  Node* context = assembler->Parameter(4);
+  Node* x_value = assembler->TruncateTaggedToFloat64(context, x);
+  Node* value = assembler->Float64Log(x_value);
+  Node* result = assembler->ChangeFloat64ToTagged(value);
+  assembler->Return(result);
+}
+
 // ES6 section 20.2.2.28 Math.round ( x )
 void Builtins::Generate_MathRound(CodeStubAssembler* assembler) {
   Generate_MathRoundingOperation(assembler, &CodeStubAssembler::Float64Round);