Fix edge case for vector section mapping

loki/transformations/single_column/tests/test_scc_vector.py

@@ -8,7 +8,7 @@
 import pytest
 
 from loki import Subroutine, Sourcefile, Dimension, fgen
-from loki.frontend import available_frontends
+from loki.frontend import available_frontends, OMNI
 from loki.ir import (
     nodes as ir, FindNodes, pragmas_attached, is_loki_pragma
 )
@@ -562,3 +562,52 @@ def test_scc_vector_section_trim_complex(
     else:
         assert assign in loop.body
         assert(len(FindNodes(ir.Assignment).visit(loop.body)) == 4)
+
+@pytest.mark.parametrize('frontend', available_frontends(
+    skip={OMNI: 'OMNI automatically expands ELSEIF into a nested ELSE=>IF.'}
+))
+@pytest.mark.parametrize('trim_vector_sections', [False, True])
+def test_scc_devector_section_special_case(frontend, horizontal, vertical, blocking, trim_vector_sections):
+    """
+    Test to highlight the limitations of vector-section trimming.
+    """
+
+    fcode_kernel = """
+    subroutine some_kernel(start, end, nlon, flag0, flag1)
+       implicit none
+
+       integer, intent(in) :: nlon, start, end
+       logical, intent(in) :: flag0, flag1
+       real, dimension(nlon) :: work
+
+       integer :: jl
+
+       if(flag0)then
+         call some_other_kernel()
+       elseif(flag1)then
+         do jl=start,end
+            work(jl) = 1.
+         enddo
+       endif
+
+    end subroutine some_kernel
+    """
+
+    routine = Subroutine.from_source(fcode_kernel, frontend=frontend)
+
+    # check whether pipeline can be applied and works as expected
+    scc_pipeline = SCCVectorPipeline(
+        horizontal=horizontal, vertical=vertical, block_dim=blocking,
+        directive='openacc', trim_vector_sections=trim_vector_sections
+    )
+    scc_pipeline.apply(routine, role='kernel', targets=['some_kernel',])
+
+    with pragmas_attached(routine, node_type=ir.Loop):
+        conditional = FindNodes(ir.Conditional).visit(routine.body)[0]
+        assert isinstance(conditional.body[0], ir.CallStatement)
+        assert len(conditional.body) == 1
+        assert isinstance(conditional.else_body[0], ir.Conditional)
+        assert len(conditional.else_body) == 1
+        assert isinstance(conditional.else_body[0].body[0], ir.Comment)
+        assert isinstance(conditional.else_body[0].body[1], ir.Loop)
+        assert conditional.else_body[0].body[1].pragma[0].content.lower() == 'loop vector'

loki/transformations/single_column/vector.py

@@ -137,7 +137,13 @@ def extract_vector_sections(cls, section, horizontal):
                 subsec_body = cls.extract_vector_sections(separator.body, horizontal)
                 if subsec_body:
                     subsections += subsec_body
-                subsec_else = cls.extract_vector_sections(separator.else_body, horizontal)
+                # we need to prevent that the whole 'else_body' is wrapped in a section,
+                # as 'Conditional's rely on the fact that the first element of the 'else_body'
+                # (if 'has_elseif') is a Conditional itself
+                if separator.has_elseif and separator.else_body:
+                    subsec_else = cls.extract_vector_sections(separator.else_body[0].body, horizontal)
+                else:
+                    subsec_else = cls.extract_vector_sections(separator.else_body, horizontal)
                 if subsec_else:
                     subsections += subsec_else