[OpenMP][Clang] Enable inscan modifier for generic datatypes (#82220)

This patch fixes the #67002 ([OpenMP][Clang] Scan Directive not
supported for Generic types). It disables the Sema checks/analysis that
are run on the helper arrays which go into the implementation of the
`omp scan` directive until the template instantiation happens.
Grateful to @alexey-bataev for suggesting these changes.

clang/lib/Sema/SemaOpenMP.cpp

@@ -4962,7 +4962,8 @@ StmtResult Sema::ActOnOpenMPRegionEnd(StmtResult S,
           if (RC->getModifier() != OMPC_REDUCTION_inscan)
             continue;
           for (Expr *E : RC->copy_array_temps())
-            MarkDeclarationsReferencedInExpr(E);
+            if (E)
+              MarkDeclarationsReferencedInExpr(E);
         }
         if (auto *AC = dyn_cast<OMPAlignedClause>(C)) {
           for (Expr *E : AC->varlists())

clang/test/OpenMP/scan_ast_print.cpp

@@ -17,6 +17,10 @@ T tmain(T argc) {
   static T a;
 #pragma omp for reduction(inscan, +: a)
   for (int i = 0; i < 10; ++i) {
+#pragma omp scan inclusive(a)
+  }
+#pragma omp parallel for reduction(inscan, +:a)
+  for (int i = 0; i < 10; ++i) {
 #pragma omp scan inclusive(a)
   }
   return a + argc;
@@ -25,15 +29,29 @@ T tmain(T argc) {
 // CHECK-NEXT: #pragma omp for reduction(inscan, +: a)
 // CHECK-NEXT: for (int i = 0; i < 10; ++i) {
 // CHECK-NEXT: #pragma omp scan inclusive(a){{$}}
+
+// CHECK: #pragma omp parallel for reduction(inscan, +: a)
+// CHECK-NEXT: for (int i = 0; i < 10; ++i) {
+// CHECK-NEXT: #pragma omp scan inclusive(a){{$}}
+
 // CHECK:      static int a;
 // CHECK-NEXT: #pragma omp for reduction(inscan, +: a)
 // CHECK-NEXT: for (int i = 0; i < 10; ++i) {
 // CHECK-NEXT: #pragma omp scan inclusive(a)
+
+// CHECK: #pragma omp parallel for reduction(inscan, +: a)
+// CHECK-NEXT: for (int i = 0; i < 10; ++i) {
+// CHECK-NEXT: #pragma omp scan inclusive(a)
+
 // CHECK:      static char a;
 // CHECK-NEXT: #pragma omp for reduction(inscan, +: a)
 // CHECK-NEXT: for (int i = 0; i < 10; ++i) {
 // CHECK-NEXT: #pragma omp scan inclusive(a)
 
+// CHECK: #pragma omp parallel for reduction(inscan, +: a)
+// CHECK-NEXT: for (int i = 0; i < 10; ++i) {
+// CHECK-NEXT: #pragma omp scan inclusive(a)
+
 int main(int argc, char **argv) {
   static int a;
 // CHECK: static int a;