Fix RegExp.prototype.compile error case

If the RegExp doesn't parse, then ES2015 specifies that
RegExp.prototype.compile does not mutate it. This patch changes
our RegExp implementation to follow that logic.

R=yangguo

Review-Url: https://codereview.chromium.org/1972093003
Cr-Commit-Position: refs/heads/master@{#36268}

src/objects.cc

@@ -15449,6 +15449,9 @@ MaybeHandle<JSRegExp> JSRegExp::Initialize(Handle<JSRegExp> regexp,
   ASSIGN_RETURN_ON_EXCEPTION(isolate, escaped_source,
                              EscapeRegExpSource(isolate, source), JSRegExp);
 
+  RETURN_ON_EXCEPTION(isolate, RegExpImpl::Compile(regexp, source, flags),
+                      JSRegExp);
+
   regexp->set_source(*escaped_source);
   regexp->set_flags(Smi::FromInt(flags));
 
@@ -15469,9 +15472,6 @@ MaybeHandle<JSRegExp> JSRegExp::Initialize(Handle<JSRegExp> regexp,
         .Check();
   }
 
-  RETURN_ON_EXCEPTION(isolate, RegExpImpl::Compile(regexp, source, flags),
-                      JSRegExp);
-
   return regexp;
 }
 

test/mjsunit/regexp-compile.js

@@ -42,3 +42,7 @@ re.compile("(y)");
 assertEquals(["y", "y"], re.exec("axyb"));
 
 assertEquals(2, re.compile.length);
+
+// If RegExp parsing fails, the RegExp is not modified
+var r = /./; try { r.compile('? invalid'); } catch(err){}
+assertEquals("/./", r.toString());