Avoid generating string representation when comparing the empty string.

3 files changed, 106 insertions, 5 deletions

diff --git a/generic/tclExecute.c b/generic/tclExecute.c
index af44323..728a847 100644
--- a/generic/tclExecute.c
+++ b/generic/tclExecute.c
@@ -5440,22 +5440,58 @@ 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);
+		{
+		    int empty;
+		    if ((empty = TclCheckEmptyString(valuePtr)) > 0) {
+			switch (TclCheckEmptyString(value2Ptr)) {
+			    case -1:
+				s1 = "";
+				s1len = 0;
+				s2 = TclGetStringFromObj(value2Ptr, &s2len);
+				break;
+			    case 0:
+				match = -1;
+				goto matchdone;
+			    case 1:
+				match = 0;
+				goto matchdone;
+			}
+		    } else if (TclCheckEmptyString(value2Ptr) > 0) {
+			switch (empty) {
+			    case -1:
+				s2 = "";
+				s2len = 0;
+				s1 = TclGetStringFromObj(valuePtr, &s1len);
+				break;
+			    case 0:
+				match = 1;
+				goto matchdone;
+			    case 1:
+				match = 0;
+				goto matchdone;
+			}
+		    } 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.
@@ -5468,6 +5504,8 @@ TEBCresume(
 	    }
 	}
 
+	matchdone:
+
 	/*
 	 * Make sure only -1,0,1 is returned
 	 * TODO: consider peephole opt.
@@ -6142,6 +6180,14 @@ 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.
+	*/
+	if (TclCheckEmptyString(valuePtr) > 0 || TclCheckEmptyString(value2Ptr) > 0) {
+	    goto stringCompare;
+	}
+
 	if (GetNumberFromObj(NULL, valuePtr, &ptr1, &type1) != TCL_OK
 		|| GetNumberFromObj(NULL, value2Ptr, &ptr2, &type2) != TCL_OK) {
 	    /*
diff --git a/generic/tclInt.h b/generic/tclInt.h
index 4db4576..4bdaf58 100644
--- a/generic/tclInt.h
+++ b/generic/tclInt.h
@@ -2735,6 +2735,10 @@ MODULE_SCOPE long	tclObjsShared[TCL_MAX_SHARED_OBJ_STATS];
 MODULE_SCOPE char *	tclEmptyStringRep;
 MODULE_SCOPE char	tclEmptyString;
 
+enum CheckEmptyStringResult {
+	TCL_EMPTYSTRING_UNKNOWN = -1, TCL_EMPTYSTRING_NO, TCL_EMPTYSTRING_YES
+};
+
 /*
  *----------------------------------------------------------------
  * Procedures shared among Tcl modules but not used by the outside world,
@@ -2875,6 +2879,7 @@ MODULE_SCOPE int	TclCheckArrayTraces(Tcl_Interp *interp, Var *varPtr,
 			    Var *arrayPtr, Tcl_Obj *name, int index);
 MODULE_SCOPE int	TclCheckBadOctal(Tcl_Interp *interp,
 			    const char *value);
+MODULE_SCOPE int	TclCheckEmptyString(Tcl_Obj *objPtr);
 MODULE_SCOPE int	TclChanCaughtErrorBypass(Tcl_Interp *interp,
 			    Tcl_Channel chan);
 MODULE_SCOPE Tcl_ObjCmdProc TclChannelNamesCmd;
@@ -4455,6 +4460,11 @@ MODULE_SCOPE void	TclDbInitNewObj(Tcl_Obj *objPtr, const char *file,
 
 #define TclIsPureByteArray(objPtr) \
 	(((objPtr)->typePtr==&tclByteArrayType) && ((objPtr)->bytes==NULL))
+#define TclIsPureDict(objPtr) \
+	(((objPtr)->bytes==NULL) && ((objPtr)->typePtr==&tclDictType))
+
+#define TclIsPureList(objPtr) \
+	(((objPtr)->bytes==NULL) && ((objPtr)->typePtr==&tclListType))
 
 /*
  *----------------------------------------------------------------
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index 1b35c56..a503392 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -434,6 +434,7 @@ Tcl_GetCharLength(
 	return length;
     }
 
+
     /*
      * OK, need to work with the object as a string.
      */
@@ -464,6 +465,50 @@ Tcl_GetCharLength(
     }
     return numChars;
 }
+
+
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TclCheckEmptyString --
+ *
+ *	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
+TclCheckEmptyString (
+    Tcl_Obj *objPtr
+) {
+    int length = -1;
+
+    if (objPtr->bytes == tclEmptyStringRep) {
+	return TCL_EMPTYSTRING_YES;
+    }
+
+    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 TCL_EMPTYSTRING_UNKNOWN;
+    }
+    return objPtr->length == 0;
+}
 
 /*
  *----------------------------------------------------------------------