Avoid generating string representation for comparisons against empty string.

3 files changed, 108 insertions, 5 deletions

diff --git a/generic/tclExecute.c b/generic/tclExecute.c
index ac4076c..67c58fc 100644
--- a/generic/tclExecute.c
+++ b/generic/tclExecute.c
@@ -5443,22 +5443,57 @@ TEBCresume(
 		}
 	    } else {
 		/*
-		 * strcmp can't do a simple memcmp in order to handle the
-		 * special Tcl \xC0\x80 null encoding for utf-8.
+		 * In order to handle the special Tcl \xC0\x80 null encoding
+		 * for utf-8, strcmp can't do a simple memcmp.
 		 */
 
-		s1 = TclGetStringFromObj(valuePtr, &s1len);
-		s2 = TclGetStringFromObj(value2Ptr, &s2len);
+		if (TclIsEmpty(valuePtr) > 0) {
+		    s1 = "";
+		    s1len = 0;
+		    switch (TclIsEmpty(value2Ptr)) {
+			case -1:
+			    s2 = TclGetStringFromObj(value2Ptr, &s2len);
+			case 0:
+			    /* Synthesize a value for comparison */
+			    s2 = "1";
+			    s2len = 1;
+			    break;
+			case 1:
+			    s2 = "";
+			    s2len = 0;
+		    }
+		} else if (TclIsEmpty(value2Ptr) > 0) {
+		    s2 = "";
+		    s2len = 0;
+		    switch (TclIsEmpty(valuePtr)) {
+			case -1:
+			    s1 = TclGetStringFromObj(valuePtr, &s1len);
+			    break;
+			case 0:
+			    /* Synthesize a value for comparison */
+			    s1 = "1";
+			    s1len = 1;
+			    break;
+			case 1:
+			    s1 = "";
+			    s1len = 0;
+		    }
+		} else {
+		    s1 = TclGetStringFromObj(valuePtr, &s1len);
+		    s2 = TclGetStringFromObj(value2Ptr, &s2len);
+		}
+
 		if (checkEq) {
 		    memCmpFn = memcmp;
 		} else {
 		    memCmpFn = (memCmpFn_t) TclpUtfNcmp2;
 		}
+
 	    }
 
 	    if (checkEq && (s1len != s2len)) {
 		match = 1;
-	    } else {
+	    }  else {
 		/*
 		 * The comparison function should compare up to the minimum
 		 * byte length only.
@@ -6169,6 +6204,20 @@ TEBCresume(
 	value2Ptr = OBJ_AT_TOS;
 	valuePtr = OBJ_UNDER_TOS;
 
+	/*
+	    Try to determine, without triggering generation of a string
+	    representation, whether one value is not a number.
+	*/
+#       define TclIsNotNumber(objPtr) ( \
+           ( TclIsEmpty((objPtr)) > 0 \
+           || ( (objPtr)->bytes != NULL && \
+           TclParseNumber( \
+               interp, (objPtr), "number", NULL, -1, NULL, 0) != TCL_OK)) \
+        )
+	if (TclIsNotNumber(valuePtr) || TclIsNotNumber(value2Ptr)) {
+	    goto stringCompare;
+	}
+
 	if (GetNumberFromObj(NULL, valuePtr, &ptr1, &type1) != TCL_OK) {
 	    /*
 	     * At least one non-numeric argument - compare as strings.
diff --git a/generic/tclInt.h b/generic/tclInt.h
index c01b0c1..817f17d 100644
--- a/generic/tclInt.h
+++ b/generic/tclInt.h
@@ -4411,6 +4411,12 @@ MODULE_SCOPE void	TclDbInitNewObj(Tcl_Obj *objPtr, const char *file,
 #define TclIsPureByteArray(objPtr) \
 	(((objPtr)->typePtr==&tclByteArrayType) && ((objPtr)->bytes==NULL))
 
+#define TclIsPureDict(objPtr) \
+	(((objPtr)->typePtr==&tclDictType) && ((objPtr)->bytes==NULL))
+
+#define TclIsPureList(objPtr) \
+	(((objPtr)->typePtr==&tclListType) && ((objPtr)->bytes==NULL))
+
 /*
  *----------------------------------------------------------------
  * Macro used by the Tcl core to compare Unicode strings. On big-endian
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index e3cede6..de3a82e 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -421,6 +421,7 @@ Tcl_GetCharLength(
 	return length;
     }
 
+
     /*
      * OK, need to work with the object as a string.
      */
@@ -439,6 +440,53 @@ Tcl_GetCharLength(
     }
     return numChars;
 }
+
+
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TclIsEmpty --
+ *
+ *	Determine whether the string value of an object is or would be the
+ *	empty string, without generating a string representation.
+ *
+ * Results:
+ *	Returns 1 if empty, 0 if not, and -1 if unknown.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+int
+TclIsEmpty (
+    Tcl_Obj *objPtr
+) {
+    int length = -1;
+
+    if (objPtr->bytes == tclEmptyStringRep) {
+	return 1;
+    }
+
+    if (TclIsPureList(objPtr)) {
+	Tcl_ListObjLength(NULL, objPtr, &length);
+	return length == 0;
+    }
+
+    if (TclIsPureDict(objPtr)) {
+	Tcl_DictObjSize(NULL, objPtr, &length);
+	return length == 0;
+    }
+
+    if (objPtr->bytes == NULL) {
+	return -1;
+    }
+    if (objPtr->bytes[0] == '\0') {
+	return 1;
+    }
+    return 0;
+}
 
 /*
  *----------------------------------------------------------------------