[flang][openacc] Allow scalar in acc cache directive (#70713)

Author: clementval

flang/docs/OpenACC.md

@@ -24,3 +24,4 @@ local:
 * The `if` clause accepts scalar integer expression in addition to scalar
   logical expression.
 * `!$acc routine` directive can be placed at the top level. 
+* `!$acc cache` directive accepts scalar variable.

flang/lib/Semantics/resolve-directives.cpp

@@ -1052,7 +1052,10 @@ static bool IsLastNameArray(const parser::Designator &designator) {
   const evaluate::DataRef dataRef{*(name.symbol)};
   return common::visit(
       common::visitors{
-          [](const evaluate::SymbolRef &ref) { return ref->Rank() > 0; },
+          [](const evaluate::SymbolRef &ref) {
+            return ref->Rank() > 0 ||
+                ref->GetType()->category() == DeclTypeSpec::Numeric;
+          },
           [](const evaluate::ArrayRef &aref) {
             return aref.base().IsSymbol() ||
                 aref.base().GetComponent().base().Rank() == 0;

flang/test/Semantics/OpenACC/acc-cache-validity.f90

@@ -29,15 +29,11 @@ program openacc_cache_validity
   !$acc cache(t%arr)
   !$acc cache(ta(1:2)%arr)
   !$acc cache(ta(1:2)%arr(1:4))
-
-  !ERROR: Only array element or subarray are allowed in CACHE directive
-  !$acc cache(ta(1:2)%s)
-
-  !ERROR: Only array element or subarray are allowed in CACHE directive
   !$acc cache(i)
+  !$acc cache(t%s)
 
   !ERROR: Only array element or subarray are allowed in CACHE directive
-  !$acc cache(t%s)
+  !$acc cache(t)
 
   !ERROR: Only array element or subarray are allowed in CACHE directive
   !$acc cache(/i/)