[builtins] Introduce proper Float64Exp operator.

src/crankshaft/mips/lithium-codegen-mips.cc

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index d351db1c56017c73afe427cc9b99c5fa1122cd1d..3cee6db394002f1c89328a1a9ca48037fc2b4dec 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -3492,16 +3492,10 @@ void LCodeGen::DoPower(LPower* instr) {
 
 
 void LCodeGen::DoMathExp(LMathExp* instr) {
-  DoubleRegister input = ToDoubleRegister(instr->value());
-  DoubleRegister result = ToDoubleRegister(instr->result());
-  DoubleRegister double_scratch1 = ToDoubleRegister(instr->double_temp());
-  DoubleRegister double_scratch2 = double_scratch0();
-  Register temp1 = ToRegister(instr->temp1());
-  Register temp2 = ToRegister(instr->temp2());
-
-  MathExpGenerator::EmitMathExp(
-      masm(), input, result, double_scratch1, double_scratch2,
-      temp1, temp2, scratch0());
+  __ PrepareCallCFunction(0, 1, scratch0());
+  __ MovToFloatParameter(ToDoubleRegister(instr->value()));
+  __ CallCFunction(ExternalReference::ieee754_exp_function(isolate()), 0, 1);
+  __ MovFromFloatResult(ToDoubleRegister(instr->result()));
 }