From 8ffb8fa76d0d34283e491044dd28385674ba113e Mon Sep 17 00:00:00 2001
From: Miguel Sofer <miguel.sofer@gmail.com>
Date: Sun, 28 Oct 2007 03:16:58 +0000
Subject: 	* generic/tclUtil.c (Tcl_ConcatObj): optimise for some of the 
 concatenees being empty objs [Bug 1447328]

---
 ChangeLog         |  5 +++++
 generic/tclUtil.c | 51 ++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index ccf0c39..5afd9c1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2007-10-28  Miguel Sofer  <msofer@users.sf.net>
+
+	* generic/tclUtil.c (Tcl_ConcatObj): optimise for some of the
+	concatenees being empty objs [Bug 1447328]
+	
 2007-10-28  Donal K. Fellows  <dkf@users.sf.net>
 
 	* generic/tclEncoding.c (TclInitEncodingSubsystem): Hard code the
diff --git a/generic/tclUtil.c b/generic/tclUtil.c
index 6a25141..54e8a04 100644
--- a/generic/tclUtil.c
+++ b/generic/tclUtil.c
@@ -11,7 +11,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclUtil.c,v 1.83 2007/10/15 21:27:48 dgp Exp $
+ * RCS: @(#) $Id: tclUtil.c,v 1.84 2007/10/28 03:17:00 msofer Exp $
  */
 
 #include "tclInt.h"
@@ -1145,14 +1145,15 @@ Tcl_ConcatObj(
     char *p;
     char *element;
     char *concatStr;
-    Tcl_Obj *objPtr;
+    Tcl_Obj *objPtr, *resPtr;
 
     /*
-     * Check first to see if all the items are of list type. If so, we will
-     * concat them together as lists, and return a list object. This is only
-     * valid when the lists have no current string representation, since we
-     * don't know what the original type was. An original string rep may have
-     * lost some whitespace info when converted which could be important.
+     * Check first to see if all the items are of list type or empty. If so,
+     * we will concat them together as lists, and return a list object. This
+     * is only valid when the lists have no current string representation,
+     * since we don't know what the original type was. An original string rep
+     * may have lost some whitespace info when converted which could be
+     * important. 
      */
 
     for (i = 0;  i < objc;  i++) {
@@ -1160,7 +1161,12 @@ Tcl_ConcatObj(
 
 	objPtr = objv[i];
 	if (objPtr->typePtr != &tclListType) {
-	    break;
+	    Tcl_GetString(objPtr);
+	    if (objPtr->length) {
+		break;
+	    } else {
+		continue;
+	    }
 	}
 	listRepPtr = (List *) objPtr->internalRep.twoPtrValue.ptr1;
 	if (objPtr->bytes != NULL && !listRepPtr->canonicalFlag) {
@@ -1171,19 +1177,38 @@ Tcl_ConcatObj(
 	Tcl_Obj **listv;
 	int listc;
 
-	objPtr = Tcl_NewListObj(0, NULL);
+	resPtr = NULL;
 	for (i = 0;  i < objc;  i++) {
 	    /*
 	     * Tcl_ListObjAppendList could be used here, but this saves us a
 	     * bit of type checking (since we've already done it). Use of
 	     * INT_MAX tells us to always put the new stuff on the end. It
 	     * will be set right in Tcl_ListObjReplace.
+	     * Note that all objs at this point are either lists or have an
+	     * empty string rep.
 	     */
-
-	    Tcl_ListObjGetElements(NULL, objv[i], &listc, &listv);
-	    Tcl_ListObjReplace(NULL, objPtr, INT_MAX, 0, listc, listv);
+	    
+	    objPtr = objv[i];
+	    if (objPtr->bytes && !objPtr->length) {
+		continue;
+	    }
+	    Tcl_ListObjGetElements(NULL, objPtr, &listc, &listv);
+	    if (listc) {
+		if (resPtr) {
+		    Tcl_ListObjReplace(NULL, resPtr, INT_MAX, 0, listc, listv);
+		} else {
+		    if (Tcl_IsShared(objPtr)) {
+			resPtr = TclListObjCopy(NULL, objPtr);
+		    } else {
+			resPtr = objPtr;
+		    }
+		}
+	    }
+	}
+	if (!resPtr) {
+	    resPtr = Tcl_NewObj();
 	}
-	return objPtr;
+	return resPtr;
     }
 
     /*
-- 
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