[flang] Check ArrayRef base for contiguity in IsSimplyContiguousHelper

[jeanPerier]

Summary

Previous code was returning true for x(:) where x is a pointer without
the contiguous attribute.
In case the array ref is a whole array section, check the base for contiguity
to solve the issue.

flang/lib/Evaluate/check-expression.cpp

Result operator()(const semantics::Symbol &symbol) const {
     }
   }
 
   Result operator()(const ArrayRef &x) const {
     const auto &symbol{x.GetLastSymbol()};
     if (!(*this)(symbol).has_value()) {
       return false;
     } else if (auto rank{CheckSubscripts(x.subscript())}) {
-      // a(:)%b(1,1) is not contiguous; a(1)%b(:,:) is
-      return *rank > 0 || x.Rank() == 0;
+      if (x.Rank() == 0) {
+        return true;
+      } else if (*rank > 0) {
+        // a(1)%b(:,:) is contiguous if an only if a(1)%b is contiguous.
+        return (*this)(x.base());
+      } else {
+        // a(:)%b(1,1) is not contiguous.
+        return false;
+      }
     } else {
       return false;
     }
   }
   Result operator()(const CoarrayRef &x) const {
     return CheckSubscripts(x.subscript()).has_value();
   }
   Result operator()(const Component &x) const {

flang/test/Semantics/assign03.f90

subroutine s12
     logical, parameter :: l1 = is_contiguous(x%a(:,:))
     logical, parameter :: l2 = is_contiguous(y(1,1)%a(1,1))
     !ERROR: Must be a constant value
     logical, parameter :: l3 = is_contiguous(y(:,1)%a(1,1))
     !ERROR: Must be a constant value
     logical, parameter :: l4 = is_contiguous(x%a(:,v))
     !ERROR: Must be a constant value
     logical, parameter :: l5 = is_contiguous(y(v,1)%a(1,1))
+    !ERROR: Must be a constant value
+    logical, parameter :: l6 = is_contiguous(p(:))
   end
   subroutine test3(b)
     integer, intent(inout) :: b(..)
     !ERROR: Must be a constant value
     integer, parameter :: i = rank(b)
   end subroutine
 
 
 end