Fix clobbered register when setting this_function variable.

src/mips/full-codegen-mips.cc

Index: src/mips/full-codegen-mips.cc
diff --git a/src/mips/full-codegen-mips.cc b/src/mips/full-codegen-mips.cc
index 2440f9838362534dd70a472b133c2670b92824a7..e6fee96d35d066e4aea276aa24f330237a0a87ef 100644
--- a/src/mips/full-codegen-mips.cc
+++ b/src/mips/full-codegen-mips.cc
@@ -252,6 +252,10 @@ void FullCodeGenerator::Generate() {
   Variable* this_function_var = scope()->this_function_var();
   if (this_function_var != nullptr) {
     Comment cmnt(masm_, "[ This function");
+    if (!function_in_register) {
+      __ lw(a1, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
+      function_in_register = true;
+    }
     SetVar(this_function_var, a1, a2, a3);
   }