[flang][OpenMP] Implement loop nest parser (#168884)

Previously, loop constructs were parsed in a piece-wise manner: the
begin directive, the body, and the end directive were parsed separately.
Later on in canonicalization they were all coalesced into a loop
construct. To facilitate that end-loop directives were given a special
treatment, namely they were parsed as OpenMP constructs. As a result
syntax errors caused by misplaced end-loop directives were handled
differently from those cause by misplaced non-loop end directives.

The new loop nest parser constructs the complete loop construct,
removing the need for the canonicalization step. Additionally, it is the
basis for parsing loop-sequence-associated constructs in the future.

It also removes the need for the special treatment of end-loop
directives. While this patch temporarily degrades the error messaging
for misplaced end-loop directives, it enables uniform handling of any
misplaced end-directives in the future.

1 files changed, 15 insertions, 21 deletions

diff --git a/flang/test/Semantics/OpenMP/loop-association.f90 b/flang/test/Semantics/OpenMP/loop-association.f90
index 9fac508e6128..b2898d3967a2 100644
--- a/flang/test/Semantics/OpenMP/loop-association.f90
+++ b/flang/test/Semantics/OpenMP/loop-association.f90
@@ -17,11 +17,13 @@
   !$omp end parallel
 
   !$omp parallel do
+  !ERROR: DO CONCURRENT loops cannot form part of a loop nest.
   DO CONCURRENT (i = 1:N)
      a = 3.14
   END DO
 
   !$omp parallel do simd
+  !ERROR: The associated loop of a loop-associated directive cannot be a DO WHILE.
   outer: DO WHILE (c > 1)
      inner: do while (b > 100)
         a = 3.14
@@ -31,7 +33,10 @@
   END DO outer
 
   ! Accept directives between parallel do and actual loop.
+  !ERROR: A DO loop must follow the PARALLEL DO directive
   !$OMP PARALLEL DO
+  !WARNING: Unrecognized compiler directive was ignored [-Wignored-directive]
+  !ERROR: Compiler directives are not allowed inside OpenMP loop constructs
   !DIR$ VECTOR ALIGNED
   DO 20 i=1,N
      a = a + 0.5
@@ -39,11 +44,14 @@
   !$OMP END PARALLEL DO
 
   c = 16
-  !ERROR: DO loop after the PARALLEL DO directive must have loop control
   !$omp parallel do
+  !ERROR: Loop control is not present in the DO LOOP
+  !ERROR: The associated loop of a loop-associated directive cannot be a DO without control.
   do
      a = 3.14
      c = c - 1
+     !ERROR: EXIT to construct outside of PARALLEL DO construct is not allowed
+     !ERROR: EXIT statement terminates associated loop of an OpenMP DO construct
      if (c < 1) exit
   enddo
 
@@ -57,9 +65,9 @@
      do 100 j=1, N
         a = 3.14
 100     continue
-    !ERROR: The ENDDO directive must follow the DO loop associated with the loop construct
     !$omp enddo
 
+  !ERROR: Non-THREADPRIVATE object 'a' in COPYIN clause
   !$omp parallel do copyin(a)
   do i = 1, N
      !$omp parallel do
@@ -74,8 +82,6 @@
   do i = 1, N
   enddo
   !$omp end parallel do
-  !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do
 
   !$omp parallel
   a = 3.0
@@ -84,27 +90,22 @@
   enddo
   !$omp end do simd
 
+  !ERROR: Non-THREADPRIVATE object 'a' in COPYIN clause
   !$omp parallel do copyin(a)
   do i = 1, N
   enddo
   !$omp end parallel
 
   a = 0.0
-  !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do
   !$omp parallel do private(c)
   do i = 1, N
      do j = 1, N
-        !ERROR: A DO loop must follow the PARALLEL DO directive
+        !ERROR: OpenMP loop construct should contain a DO-loop or a loop-nest-generating OpenMP construct
         !$omp parallel do shared(b)
         a = 3.14
      enddo
-     !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-     !$omp end parallel do
   enddo
   a = 1.414
-  !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do
 
   do i = 1, N
      !$omp parallel do
@@ -112,29 +113,22 @@
         a = 3.14
      enddo
   enddo
-  !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do
 
-  !ERROR: A DO loop must follow the PARALLEL DO directive
+  !ERROR: OpenMP loop construct should contain a DO-loop or a loop-nest-generating OpenMP construct
   !$omp parallel do private(c)
 5 FORMAT (1PE12.4, I10)
   do i=1, N
      a = 3.14
   enddo
-  !ERROR: The END PARALLEL DO directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do
 
   !$omp parallel do simd
   do i = 1, N
      a = 3.14
   enddo
   !$omp end parallel do simd
-  !ERROR: The END PARALLEL DO SIMD directive must follow the DO loop associated with the loop construct
-  !$omp end parallel do simd
 
-  !ERROR: A DO loop must follow the SIMD directive
+  !ERROR: OpenMP loop construct should contain a DO-loop or a loop-nest-generating OpenMP construct
   !$omp simd
-    a = i + 1
-  !ERROR: The END SIMD directive must follow the DO loop associated with the loop construct
   !$omp end simd
+   a = i + 1
 end