C++: Fix global flow without an SSA definition

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternals.qll

@@ -155,11 +155,13 @@ private newtype TDefOrUseImpl =
   TGlobalUse(GlobalLikeVariable v, IRFunction f, int indirectionIndex) {
     // Represents a final "use" of a global variable to ensure that
     // the assignment to a global variable isn't ruled out as dead.
-    exists(VariableAddressInstruction vai, int defIndex |
+    exists(VariableAddressInstruction vai, int i |
       vai.getEnclosingIRFunction() = f and
       vai.getAstVariable() = v and
-      isDef(_, _, _, vai, _, defIndex) and
-      indirectionIndex = [0 .. defIndex] + 1
+      indirectionIndex = [0 .. i] + 1
+    |
+      isDef(_, _, _, vai, indirectionIndex, i) or
+      isUse(_, _, vai, indirectionIndex, i)
     )
   } or
   TGlobalDefImpl(GlobalLikeVariable v, IRFunction f, int indirectionIndex) {

cpp/ql/test/library-tests/dataflow/dataflow-tests/dataflow-consistency.expected

@@ -44,6 +44,7 @@ postWithInFlow
 | example.c:28:23:28:25 | pos [inner post update] | PostUpdateNode should not be the target of local flow. |
 | globals.cpp:13:5:13:19 | flowTestGlobal1 [post update] | PostUpdateNode should not be the target of local flow. |
 | globals.cpp:23:5:23:19 | flowTestGlobal2 [post update] | PostUpdateNode should not be the target of local flow. |
+| globals.cpp:34:18:34:18 | x [post update] | PostUpdateNode should not be the target of local flow. |
 | lambdas.cpp:23:3:23:14 | v [post update] | PostUpdateNode should not be the target of local flow. |
 | lambdas.cpp:43:3:43:3 | c [post update] | PostUpdateNode should not be the target of local flow. |
 | ref.cpp:11:5:11:7 | lhs [post update] | PostUpdateNode should not be the target of local flow. |

cpp/ql/test/library-tests/dataflow/dataflow-tests/globals.cpp

@@ -22,3 +22,20 @@ void readGlobal2() {
 void writeGlobal2() {
     flowTestGlobal2 = source();
 }
+
+namespace MyNamespace {
+    struct A {
+        int x;
+    };
+
+    A global_a;
+
+    void set_without_ssa_def() {
+        global_a.x = source();
+    }
+
+    void call_set_without_ssa_def() {
+        set_without_ssa_def();
+        sink(global_a.x); // $ ir MISSING: ast
+    }
+}