C++: Add more CWE-119 testcases with compound assignments instead of increments.

cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/OverflowBuffer.expected

@@ -47,6 +47,9 @@
 | tests.cpp:546:6:546:10 | call to fread | This 'fread' operation may access 400 bytes but the $@ is only 100 bytes. | tests.cpp:532:7:532:16 | charBuffer | destination buffer |
 | tests.cpp:569:6:569:15 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:565:7:565:12 | buffer | array |
 | tests.cpp:577:7:577:13 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:565:7:565:12 | buffer | array |
+| tests.cpp:637:6:637:15 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:633:7:633:12 | buffer | array |
+| tests.cpp:645:7:645:13 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:633:7:633:12 | buffer | array |
+| tests.cpp:654:6:654:12 | access to array | This array indexing operation accesses a negative index -1 on the $@. | tests.cpp:633:7:633:12 | buffer | array |
 | tests_restrict.c:12:2:12:7 | call to memcpy | This 'memcpy' operation accesses 2 bytes but the $@ is only 1 byte. | tests_restrict.c:7:6:7:13 | smallbuf | source buffer |
 | unions.cpp:26:2:26:7 | call to memset | This 'memset' operation accesses 200 bytes but the $@ is only 100 bytes. | unions.cpp:21:10:21:11 | mu | destination buffer |
 | unions.cpp:30:2:30:7 | call to memset | This 'memset' operation accesses 200 bytes but the $@ is only 100 bytes. | unions.cpp:15:7:15:11 | small | destination buffer |

cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/UnboundedWrite.expected

@@ -1,6 +1,6 @@
 edges
 | main.cpp:6:27:6:30 | argv indirection | main.cpp:10:20:10:23 | argv indirection |
-| main.cpp:10:20:10:23 | argv indirection | tests.cpp:631:32:631:35 | argv indirection |
+| main.cpp:10:20:10:23 | argv indirection | tests.cpp:657:32:657:35 | argv indirection |
 | tests.cpp:613:19:613:24 | source indirection | tests.cpp:615:17:615:22 | source indirection |
 | tests.cpp:622:19:622:24 | source indirection | tests.cpp:625:2:625:16 | ... = ... indirection |
 | tests.cpp:625:2:625:16 | ... = ... indirection | tests.cpp:625:4:625:7 | s indirection [post update] [home indirection] |
@@ -8,10 +8,10 @@ edges
 | tests.cpp:628:14:628:14 | s indirection [home indirection] | tests.cpp:628:14:628:19 | home indirection |
 | tests.cpp:628:14:628:14 | s indirection [home indirection] | tests.cpp:628:16:628:19 | home indirection |
 | tests.cpp:628:16:628:19 | home indirection | tests.cpp:628:14:628:19 | home indirection |
-| tests.cpp:631:32:631:35 | argv indirection | tests.cpp:656:9:656:15 | access to array indirection |
-| tests.cpp:631:32:631:35 | argv indirection | tests.cpp:657:9:657:15 | access to array indirection |
-| tests.cpp:656:9:656:15 | access to array indirection | tests.cpp:613:19:613:24 | source indirection |
-| tests.cpp:657:9:657:15 | access to array indirection | tests.cpp:622:19:622:24 | source indirection |
+| tests.cpp:657:32:657:35 | argv indirection | tests.cpp:682:9:682:15 | access to array indirection |
+| tests.cpp:657:32:657:35 | argv indirection | tests.cpp:683:9:683:15 | access to array indirection |
+| tests.cpp:682:9:682:15 | access to array indirection | tests.cpp:613:19:613:24 | source indirection |
+| tests.cpp:683:9:683:15 | access to array indirection | tests.cpp:622:19:622:24 | source indirection |
 nodes
 | main.cpp:6:27:6:30 | argv indirection | semmle.label | argv indirection |
 | main.cpp:10:20:10:23 | argv indirection | semmle.label | argv indirection |
@@ -23,9 +23,9 @@ nodes
 | tests.cpp:628:14:628:14 | s indirection [home indirection] | semmle.label | s indirection [home indirection] |
 | tests.cpp:628:14:628:19 | home indirection | semmle.label | home indirection |
 | tests.cpp:628:16:628:19 | home indirection | semmle.label | home indirection |
-| tests.cpp:631:32:631:35 | argv indirection | semmle.label | argv indirection |
-| tests.cpp:656:9:656:15 | access to array indirection | semmle.label | access to array indirection |
-| tests.cpp:657:9:657:15 | access to array indirection | semmle.label | access to array indirection |
+| tests.cpp:657:32:657:35 | argv indirection | semmle.label | argv indirection |
+| tests.cpp:682:9:682:15 | access to array indirection | semmle.label | access to array indirection |
+| tests.cpp:683:9:683:15 | access to array indirection | semmle.label | access to array indirection |
 subpaths
 #select
 | tests.cpp:615:2:615:7 | call to strcpy | main.cpp:6:27:6:30 | argv indirection | tests.cpp:615:17:615:22 | source indirection | This 'call to strcpy' with input from $@ may overflow the destination. | main.cpp:6:27:6:30 | argv indirection | a command-line argument |

cpp/ql/test/query-tests/Security/CWE/CWE-119/semmle/tests/tests.cpp

@@ -628,6 +628,32 @@ void test25(char* source) {
 	strcpy(buf, s.home); // BAD
 }
 
+void test26(bool cond)
+{
+	char buffer[100];
+	char *ptr;
+	int i;
+
+	if (buffer[-1] == 0) { return; } // BAD: accesses buffer[-1]
+
+	ptr = buffer;
+	if (cond)
+	{
+		ptr += 1;
+		if (ptr[-1] == 0) { return; } // GOOD: accesses buffer[0]
+	} else {
+		if (ptr[-1] == 0) { return; } // BAD: accesses buffer[-1]
+	}
+	if (ptr[-1] == 0) { return; } // BAD: accesses buffer[-1] or buffer[0] [NOT DETECTED]
+
+	ptr = buffer;
+	for (i = 0; i < 2; i++)
+	{
+		ptr += 1;
+	}
+	if (ptr[-1] == 0) { return; } // GOOD: accesses buffer[1] [FALSE POSITIVE]
+}
+
 int tests_main(int argc, char *argv[])
 {
 	long long arr17[19];