Add append optimisation for string '+', and don't append to flat/native/etc strings (fix #1746)

Author: gfwilliams

ChangeLog

@@ -74,6 +74,7 @@
             Bangle.js: Remove deprecated Bangle.menu
             Ensure it's possible to get a solid background when using 4x6 font
             Bangle.js: Add Bangle.showLauncher
+            Add append optimisation for string '+', and don't append to flat/native/etc strings (fix #1746)
 
      2v04 : Allow \1..\9 escape codes in RegExp
             ESP8266: reading storage is not working for boot from user2 (fix #1507)

src/jsparse.c

@@ -1998,7 +1998,7 @@ NO_INLINE JsVar *__jspeAssignmentExpression(JsVar *lhs) {
         else if (op==LEX_RSHIFTUNSIGNEDEQUAL) op=LEX_RSHIFTUNSIGNED;
         if (op=='+' && jsvIsName(lhs)) {
           JsVar *currentValue = jsvSkipName(lhs);
-          if (jsvIsString(currentValue) && !jsvIsFlatString(currentValue) && jsvGetRefs(currentValue)==1 && rhs!=currentValue) {
+          if (jsvIsBasicString(currentValue) && jsvGetRefs(currentValue)==1 && rhs!=currentValue) {
             /* A special case for string += where this is the only use of the string
              * and we're not appending to ourselves. In this case we can do a
              * simple append (rather than clone + append)*/

src/jsvar.c

@@ -71,7 +71,7 @@ bool jsvIsInt(const JsVar *v) { return v && ((v->flags&JSV_VARTYPEMASK)==JSV_INT
 bool jsvIsFloat(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)==JSV_FLOAT; }
 bool jsvIsBoolean(const JsVar *v) { return v && ((v->flags&JSV_VARTYPEMASK)==JSV_BOOLEAN || (v->flags&JSV_VARTYPEMASK)==JSV_NAME_INT_BOOL); }
 bool jsvIsString(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)>=_JSV_STRING_START && (v->flags&JSV_VARTYPEMASK)<=_JSV_STRING_END; } ///< String, or a NAME too
-bool jsvIsBasicString(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)>=JSV_STRING_0 && (v->flags&JSV_VARTYPEMASK)<=JSV_STRING_MAX; } ///< Just a string (NOT a name)
+bool jsvIsBasicString(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)>=JSV_STRING_0 && (v->flags&JSV_VARTYPEMASK)<=JSV_STRING_MAX; } ///< Just a string (NOT a name/flatstr/nativestr or flashstr)
 bool jsvIsStringExt(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)>=JSV_STRING_EXT_0 && (v->flags&JSV_VARTYPEMASK)<=JSV_STRING_EXT_MAX; } ///< The extra bits dumped onto the end of a string to store more data
 bool jsvIsFlatString(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)==JSV_FLAT_STRING; }
 bool jsvIsNativeString(const JsVar *v) { return v && (v->flags&JSV_VARTYPEMASK)==JSV_NATIVE_STRING; }
@@ -3485,8 +3485,12 @@ JsVar *jsvMathsOp(JsVar *a, JsVar *b, int op) {
       return 0;
     }
     if (op=='+') {
-      JsVar *v = jsvCopy(da, false);
-      // TODO: can we be fancy and not copy da if we know it isn't reffed? what about locks?
+      JsVar *v;
+      // Don't copy 'da' if it's not used elsewhere (eg we made it in 'jsvAsString' above)
+      if (jsvIsBasicString(da) && jsvGetLocks(da)==1 && jsvGetRefs(da)==0)
+        v = jsvLockAgain(da);
+      else
+        v = jsvCopy(da, false);
       if (v) // could be out of memory
         jsvAppendStringVarComplete(v, db);
       jsvUnLock2(da, db);