Another TclStringCatObjv optimization to delay/avoid string rep generation.

2 files changed, 57 insertions, 11 deletions

diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index aae52ba..aa99545 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -2916,10 +2916,10 @@ TclStringCatObjv(
 		    last = objc - oc;
 		    if (length == 0) {
 			first = last;
-		    }
-		    if ((length += numBytes) < 0) {
+		    } else if (numBytes > INT_MAX - length) {
 			goto overflow;
 		    }
+		    length += numBytes;
 		}
 	    }
 	} while (--oc);
@@ -2937,14 +2937,16 @@ TclStringCatObjv(
 		    last = objc - oc;
 		    if (length == 0) {
 			first = last;
-		    }
-		    if ((length += numChars) < 0) {
+		    } else if (numChars > INT_MAX - length) {
 			goto overflow;
 		    }
+		    length += numChars;
 		}
 	    }
 	} while (--oc);
     } else {
+	Tcl_Obj *pendingPtr = NULL;
+
 	/* Result will be concat of string reps. Pre-size it. */
 	ov = objv; oc = objc;
 	do {
@@ -2952,15 +2954,29 @@ TclStringCatObjv(
 
 	    objPtr = *ov++;
 
-	    Tcl_GetStringFromObj(objPtr, &numBytes);	/* PANIC? */
-	    if (numBytes) {
+	    if ((length == 0) && (objPtr->bytes == NULL) && !pendingPtr) {
+		/* No string rep; Take the chance we can avoid making it */
+
+		last = objc - oc;
+		first = last;
+		pendingPtr = objPtr;
+	    } else {
+
+		Tcl_GetStringFromObj(objPtr, &numBytes); /* PANIC? */
+		if (numBytes == 0) {
+		    continue;
+		}
 		last = objc - oc;
+		if (pendingPtr) {
+		    Tcl_GetStringFromObj(pendingPtr, &length); /* PANIC? */
+		    pendingPtr = NULL;
+		}
 		if (length == 0) {
 		    first = last;
-		}
-		if ((length += numBytes) < 0) {
+		} else if (numBytes > INT_MAX - length) {
 		    goto overflow;
 		}
+		length += numBytes;
 	    }
 	} while (--oc);
     }
@@ -3073,9 +3089,9 @@ TclStringCatObjv(
 		return TCL_ERROR;
 	    }
 	    dst = Tcl_GetString(objResultPtr) + start;
-	    if (length > start) {
-		TclFreeIntRep(objResultPtr);
-	    }
+
+	    /* assert ( length > start ) */
+	    TclFreeIntRep(objResultPtr);
 	} else {
 	    objResultPtr = Tcl_NewObj();	/* PANIC? */
 	    if (0 == Tcl_AttemptSetObjLength(objResultPtr, length)) {
diff --git a/tests/string.test b/tests/string.test
index fa7f8fb..9c43f29 100644
--- a/tests/string.test
+++ b/tests/string.test
@@ -1994,6 +1994,36 @@ test string-29.4 {string cat, many args} {
     set r2 [string compare $xx [eval "string cat $vvs"]]
     list $r1 $r2
 } {0 0}
+test string-29.5 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list x] [list]]
+} -match glob -result {*no string representation}
+test string-29.6 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list] [list x]]
+} -match glob -result {*no string representation}
+test string-29.7 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list x] [list] [list]]
+} -match glob -result {*no string representation}
+test string-29.8 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list] [list x] [list]]
+} -match glob -result {*no string representation}
+test string-29.9 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list] [list] [list x]]
+} -match glob -result {*no string representation}
+test string-29.10 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat [list x] [list x]]
+} -match glob -result {*, string representation "xx"}
+test string-29.11 {string cat, efficiency} -body {
+    tcl::unsupported::representation \
+	[string cat [list x] [encoding convertto utf-8 {}]]
+} -match glob -result {*no string representation}
+test string-29.12 {string cat, efficiency} -body {
+    tcl::unsupported::representation \
+	[string cat [encoding convertto utf-8 {}] [list x]]
+} -match glob -result {*, string representation "x"}
+test string-29.13 {string cat, efficiency} -body {
+    tcl::unsupported::representation [string cat \
+	[encoding convertto utf-8 {}] [encoding convertto utf-8 {}] [list x]]
+} -match glob -result {*, string representation "x"}