[flang] Fold IS_CONTIGUOUS of component refs with non-contiguous base (#69327)

Author: jeanPerier

flang/lib/Evaluate/check-expression.cpp

@@ -821,8 +821,13 @@ class IsContiguousHelper
     if (x.base().Rank() == 0) {
       return (*this)(x.GetLastSymbol());
     } else {
-      // TODO could be true if base contiguous and this is only component, or
-      // if base has only one element?
+      if (Result baseIsContiguous{(*this)(x.base())}) {
+        if (!*baseIsContiguous) {
+          return false;
+        }
+        // TODO could be true if base contiguous and this is only component, or
+        // if base has only one element?
+      }
       return std::nullopt;
     }
   }

flang/test/Evaluate/folding09.f90

@@ -56,4 +56,13 @@ subroutine test(arr1, arr2, arr3, mat, alloc)
       end block
     end associate
   end subroutine
+  subroutine test2(x, vec)
+    type t
+      integer :: i
+    end type
+    type(t) :: x(100)
+    integer(8) :: vec(10)
+    integer(kind=merge(1,-1, .not. is_contiguous(x(1:50:2)%i)))    t01
+    integer(kind=merge(1,-1, .not. is_contiguous(x(vec)%i)))       t02
+  end subroutine
 end module