From 61df5f46580699c45d9263e3e98a0cf3f2006672 Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Thu, 13 Oct 2016 15:37:45 +0000
Subject: Streamline the substring copying case of [string replace] bytecode
 execution.

---
 generic/tclExecute.c | 66 ++++++++++++++++++----------------------------------
 1 file changed, 23 insertions(+), 43 deletions(-)

diff --git a/generic/tclExecute.c b/generic/tclExecute.c
index 34d92d3..cd27f6b 100644
--- a/generic/tclExecute.c
+++ b/generic/tclExecute.c
@@ -5804,57 +5804,37 @@ TEBCresume(
 	 * Remove substring using copying.
 	 */
 
-	if (length3 == 0) {
-	    if (fromIdx > 0) {
-		objResultPtr = Tcl_NewUnicodeObj(ustring1, fromIdx);
-		if (toIdx < length) {
-		    Tcl_AppendUnicodeToObj(objResultPtr, ustring1 + toIdx + 1,
-			    length - toIdx);
-		}
-	    } else {
-		objResultPtr = Tcl_NewUnicodeObj(ustring1 + toIdx + 1,
-			length - toIdx);
-	    }
-	    TclDecrRefCount(value3Ptr);
-	    TRACE_APPEND(("\"%.30s\"\n", O2S(objResultPtr)));
-	    NEXT_INST_F(1, 1, 1);
-	}
-
-	/*
-	 * Splice string pieces by full copying.
-	 */
-
+	objResultPtr = NULL;
 	if (fromIdx > 0) {
 	    objResultPtr = Tcl_NewUnicodeObj(ustring1, fromIdx);
-	    Tcl_AppendObjToObj(objResultPtr, value3Ptr);
-	    if (toIdx < length) {
-		Tcl_AppendUnicodeToObj(objResultPtr, ustring1 + toIdx + 1,
-			length - toIdx);
+	}
+	if (length3 > 0) {
+	    if (objResultPtr) {
+		Tcl_AppendObjToObj(objResultPtr, value3Ptr);
+	    } else if (Tcl_IsShared(value3Ptr)) {
+		objResultPtr = Tcl_DuplicateObj(value3Ptr);
+	    } else {
+		objResultPtr = value3Ptr;
 	    }
-	} else if (Tcl_IsShared(value3Ptr)) {
-	    objResultPtr = Tcl_DuplicateObj(value3Ptr);
-	    if (toIdx < length) {
+	}
+	if (toIdx < length) {
+	    if (objResultPtr) {
 		Tcl_AppendUnicodeToObj(objResultPtr, ustring1 + toIdx + 1,
 			length - toIdx);
-	    }
-	} else {
-	    /*
-	     * Be careful with splicing the stack in this case; we have a
-	     * refCount:1 object in value3Ptr and we want to append to it and
-	     * make it be the refCount:1 object at the top of the stack
-	     * afterwards. [Bug 82e7f67325]
-	     */
-
-	    if (toIdx < length) {
-		Tcl_AppendUnicodeToObj(value3Ptr, ustring1 + toIdx + 1,
+	    } else {
+		objResultPtr = Tcl_NewUnicodeObj(ustring1 + toIdx + 1,
 			length - toIdx);
 	    }
-	    TRACE_APPEND(("\"%.30s\"\n", O2S(value3Ptr)));
-	    TclDecrRefCount(valuePtr);
-	    OBJ_AT_TOS = value3Ptr;	/* Tricky! */
-	    NEXT_INST_F(1, 0, 0);
 	}
-	TclDecrRefCount(value3Ptr);
+	if (objResultPtr == NULL) {
+	    /* This has to be the case [string replace $s 0 end {}] */
+	    /* which has result {} which is same as value3Ptr. */
+	    objResultPtr = value3Ptr;
+	}
+	if (objResultPtr != value3Ptr) {
+	    /* See [Bug 82e7f67325] */
+	    TclDecrRefCount(value3Ptr);
+	}
 	TRACE_APPEND(("\"%.30s\"\n", O2S(objResultPtr)));
 	NEXT_INST_F(1, 1, 1);
 
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