C++: Handle constant variable accesses in SimpleRangeAnalysis.qll

cpp/ql/src/semmle/code/cpp/rangeanalysis/SimpleRangeAnalysis.qll

@@ -91,13 +91,30 @@ private float wideningUpperBounds(ArithmeticType t) {
   result = 1.0 / 0.0 // +Inf
 }
 
+/**
+ * Gets the value of the expression `e`, if it is a constant.
+ * This predicate also handles the case of constant variables initialized in compilation units,
+ * which doesn't necessarily have a getValue() result from the extractor.
+ */
+private string getValue(Expr e) {
+  if exists(e.getValue())
+  then result = e.getValue()
+  else
+    exists(VariableAccess access, Variable v |
+      e = access and
+      v = access.getTarget() and
+      v.getType().isConst() and
+      result = getValue(v.getAnAssignedValue())
+    )
+}
+
 /** Set of expressions which we know how to analyze. */
 private predicate analyzableExpr(Expr e) {
   // The type of the expression must be arithmetic. We reuse the logic in
   // `exprMinVal` to check this.
   exists(exprMinVal(e)) and
   (
-    exists(e.getValue().toFloat()) or
+    exists(getValue(e).toFloat()) or
     e instanceof UnaryPlusExpr or
     e instanceof UnaryMinusExpr or
     e instanceof MinExpr or