[flang][openacc] Fix gang-argument parsing and add validity tests for !$acc loop

[clementval]

Summary

This patch fix the prasing for the gang-arg values for the gang clause. It also adds
some clause validity tests for the loop construct.

[klausler]

flang/lib/Parser/openacc-parsers.cpp

150

","_tok / "STATIC:"_tok >> can be written better as just ", STATIC" >>.

The production does not match the comment.

[clementval]

Rebase + address minor comments

flang/lib/Parser/openacc-parsers.cpp

 // tile size is one of:
 //   * (represented as an empty std::optional<ScalarIntExpr>)
 //   constant-int-expr
 TYPE_PARSER(construct<AccTileExpr>(scalarIntConstantExpr) ||
     construct<AccTileExpr>(
         "*" >> construct<std::optional<ScalarIntConstantExpr>>()))
 TYPE_PARSER(construct<AccTileExprList>(nonemptyList(Parser<AccTileExpr>{})))
 
-// 2.9 (1607) gang-arg is one of:
-//   [num:]int-expr
-//   static:size-expr
-TYPE_PARSER(construct<AccGangArgument>(maybe(scalarIntExpr),
-                maybe(","_tok / "STATIC:" >> Parser<AccSizeExpr>{})) ||
-    construct<AccGangArgument>(maybe("NUM:" >> scalarIntExpr),
-        maybe(","_tok / "STATIC:" >> Parser<AccSizeExpr>{})))
+// 2.9 (1607) gang-arg is:
+//   [[num:]int-expr][[,]static:size-expr]
+TYPE_PARSER(construct<AccGangArgument>(
+    maybe(("NUM:"_tok >> scalarIntExpr || scalarIntExpr)),
+    maybe(", STATIC:" >> Parser<AccSizeExpr>{})))
 
 // 2.5.13 Reduction
 // Operator for reduction
 TYPE_PARSER(sourced(construct<AccReductionOperator>(
     first("+" >> pure(AccReductionOperator::Operator::Plus),
         "*" >> pure(AccReductionOperator::Operator::Multiply),
         "MAX" >> pure(AccReductionOperator::Operator::Max),
         "MIN" >> pure(AccReductionOperator::Operator::Min),

flang/test/Semantics/acc-clause-validity.f90

 !   2.11 Parallel Loop
 !   2.11 Kernels Loop
 !   2.11 Serial Loop
 
 program openacc_clause_validity
 
   implicit none
 
-  integer :: i, j, b
+  integer :: i, j, b, gang_size, vector_size, worker_size
   integer, parameter :: N = 256
   integer, dimension(N) :: c
   logical, dimension(N) :: d, e
   real :: reduction_r
   logical :: reduction_l
   real(8), dimension(N, N) :: aa
 
   !ERROR: At least one clause is required on the DECLARE directive
   !$acc declare
-  real(8) :: a(256)
+  real(8), dimension(N) :: a
 
   !ERROR: At least one of ATTACH, COPYIN, CREATE clause must appear on the ENTER DATA directive
   !$acc enter data
 
   !ERROR: Only the READONLY modifier is allowed for the COPYIN clause on the ENTER DATA directive
   !$acc enter data copyin(zero: i)
 
   !ERROR: Only the ZERO modifier is allowed for the CREATE clause on the ENTER DATA directive
program openacc_clause_validity
   !$acc parallel device_type(*) num_gangs(2)
   !$acc loop
   do i = 1, N
     a(i) = 3.14
   end do
   !$acc end parallel
 
   !$acc parallel
+  !$acc loop seq
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop independent
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop auto
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop vector
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop vector(10)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop vector(vector_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop vector(length: vector_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop worker
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop worker(10)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop worker(worker_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop worker(num: worker_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop gang(gang_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop gang(num: gang_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop gang(gang_size, static:*)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop gang(num: gang_size, static:*)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop gang(num: gang_size, static: gang_size)
+  do i = 1, N
+    a(i) = 3.14
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop private(b, a(:))
+  do i = 1, N
+    a(i) = b
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop tile(*)
+  do i = 1, N
+    a(i) = b
+  end do
+  !$acc end parallel
+
+  !$acc parallel
+  !$acc loop tile(2, 2)
+  do i = 1, N
+    do j = 1, N
+      a(i) = b
+    end do
+  end do
+  !$acc end parallel
+
+  !$acc parallel
   !ERROR: The parameter of the COLLAPSE clause must be a constant positive integer expression
   !$acc loop collapse(-1)
   do i = 1, N
     do j = 1, N
       a(i) = 3.14 + j
     end do
   end do
   !$acc end parallel