C++: restrict global variable IR generation

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/IRConstruction.qll

@@ -37,7 +37,14 @@ module Raw {
   predicate functionHasIR(Function func) { exists(getTranslatedFunction(func)) }
 
   cached
-  predicate varHasIRFunc(GlobalOrNamespaceVariable var) { any() } // TODO: restrict?
+  predicate varHasIRFunc(GlobalOrNamespaceVariable var) {
+    var.hasInitializer() and
+    (
+      not var.getType().isDeeplyConst()
+      or
+      var.getInitializer().getExpr() instanceof StringLiteral
+    )
+  }
 
   cached
   predicate hasInstruction(TranslatedElement element, InstructionTag tag) {

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -119,7 +119,7 @@ private predicate ignoreExprOnly(Expr expr) {
   exists(NewOrNewArrayExpr new | expr = new.getAllocatorCall().getArgument(0))
   or
   not translateFunction(expr.getEnclosingFunction()) and
-  not expr.getEnclosingVariable() instanceof GlobalOrNamespaceVariable
+  not Raw::varHasIRFunc(expr.getEnclosingVariable())
   or
   // We do not yet translate destructors properly, so for now we ignore the
   // destructor call. We do, however, translate the expression being
@@ -665,7 +665,7 @@ newtype TTranslatedElement =
   } or
   // The side effect that initializes newly-allocated memory.
   TTranslatedAllocationSideEffect(AllocationExpr expr) { not ignoreSideEffects(expr) } or
-  TTranslatedGlobalOrNamespaceVarInit(GlobalOrNamespaceVariable var) { var.hasInitializer() }
+  TTranslatedGlobalOrNamespaceVarInit(GlobalOrNamespaceVariable var) { Raw::varHasIRFunc(var) }
 
 /**
  * Gets the index of the first explicitly initialized element in `initList`