[SYCL] Fix bug with constexpr recursion (#4257)

Commit 9a9a018 introduced a regression in following case - 

E.g.

```
  struct ObjInit {
    int a;
  } objbar = {constexpr_recurse(1)};
```

The assert was hit when DeclStmt contains both TypeDecl and VarDecl i.e. a CXXRecordDecl which is not constexpr and a VarDecl which is. This PR removes code added in call graph creation. This code is not technically not required since the AST visitor in SemaSYCL, will handle non-traversal of nodes representing constexpr variables.

Closes: #4048

Signed-off-by: Elizabeth Andrews <elizabeth.andrews@intel.com>

Author: elizabethandrews

clang/lib/Analysis/CallGraph.cpp

@@ -150,24 +150,6 @@ class CGBuilder : public StmtVisitor<CGBuilder> {
     StmtVisitor::VisitIfStmt(If);
   }
 
-  void VisitDeclStmt(DeclStmt *DS) {
-    if (G->shouldSkipConstantExpressions()) {
-      auto IsConstexprVarDecl = [](Decl *D) {
-        if (const auto *VD = dyn_cast<VarDecl>(D))
-          return VD->isConstexpr();
-        return false;
-      };
-      if (llvm::any_of(DS->decls(), IsConstexprVarDecl)) {
-        assert(llvm::all_of(DS->decls(), IsConstexprVarDecl) &&
-               "Situation where a decl-group would be a mix of decl types, or "
-               "constexpr and not?");
-        return;
-      }
-    }
-
-    StmtVisitor::VisitDeclStmt(DS);
-  }
-
   void VisitChildren(Stmt *S) {
     for (Stmt *SubStmt : S->children())
       if (SubStmt)

clang/test/SemaSYCL/allow-constexpr-recursion.cpp

@@ -8,7 +8,7 @@ sycl::queue q;
 
 constexpr int constexpr_recurse1(int n);
 
-// expected-note@+1 5{{function implemented using recursion declared here}}
+// expected-note@+1 6{{function implemented using recursion declared here}}
 constexpr int constexpr_recurse(int n) {
   if (n)
     return constexpr_recurse1(n - 1);
@@ -87,6 +87,10 @@ void constexpr_recurse_test() {
     k = constexpr_recurse(1);
   else
     constexpr int l = test_constexpr_context(constexpr_recurse(1));
+
+  static constexpr struct ConstExprObjInit {
+    int a;
+  } objfoo = {constexpr_recurse(1)};
 }
 
 void constexpr_recurse_test_err() {
@@ -114,6 +118,11 @@ void constexpr_recurse_test_err() {
     j = constexpr_recurse(5);
     break;
   }
+
+  // expected-error@+3{{SYCL kernel cannot call a recursive function}}
+  struct ObjInit {
+    int a;
+  } objbar = {constexpr_recurse(1)};
 }
 
 int main() {