[Flang][OpenMP] Add Lowering support for Collapse with Taskloop (llvm#166791)

Support for lowering collapse already exists within
`genLoopNestClauses`, which is called when lowering taskloop. However,
the TODO message still included the Collapse clause, so it was not
activated. By removing this, it enables lowering of the Collapse clause
in taskloop.

Author: Stylie777

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -1781,8 +1781,6 @@ static void genTaskloopClauses(
   cp.processPriority(stmtCtx, clauseOps);
   cp.processReduction(loc, clauseOps, reductionSyms);
   cp.processUntied(clauseOps);
-
-  cp.processTODO<clause::Collapse>(loc, llvm::omp::Directive::OMPD_taskloop);
 }
 
 static void genTaskwaitClauses(lower::AbstractConverter &converter,

flang/test/Lower/OpenMP/Todo/taskloop-collapse.f90

@@ -0,0 +1,34 @@
+! Test the collapse clause when being used with the taskloop construct
+! RUN: bbc -emit-hlfir -fopenmp -fopenmp-version=45 %s -o - 2>&1 | FileCheck %s
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -fopenmp-version=45 %s -o - 2>&1 | FileCheck %s
+
+! CHECK-LABEL: omp.private
+! CHECK-SAME: {type = private} @[[J_PRIVATE:.*]] : i32
+! CHECK-LABEL: omp.private
+! CHECK-SAME: {type = private} @[[I_PRIVATE:.*]] : i32
+! CHECK-LABEL: omp.private
+! CHECK-SAME: {type = firstprivate} @[[SUM_FIRSTPRIVATE:.*]] : i32 copy
+
+! CHECK-LABEL: func.func @_QPtest()
+! CHECK: %[[ALLOCA_I:.*]] = fir.alloca i32 {bindc_name = "i", uniq_name = "_QFtestEi"}
+! CHECK: %[[DECLARE_I:.*]]:2 = hlfir.declare %1 {uniq_name = "_QFtestEi"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK: %[[ALLOCA_J:.*]] = fir.alloca i32 {bindc_name = "j", uniq_name = "_QFtestEj"}
+! CHECK: %[[DECLARE_J:.*]]:2 = hlfir.declare %3 {uniq_name = "_QFtestEj"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK: %[[ALLOCA_SUM:.*]] = fir.alloca i32 {bindc_name = "sum", uniq_name = "_QFtestEsum"}
+! CHECK: %[[DECLARE_SUM:.*]]:2 = hlfir.declare %5 {uniq_name = "_QFtestEsum"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+
+subroutine test()
+    integer :: i, j, sum
+
+    !$omp taskloop collapse(2)
+    ! CHECK-LABEL: omp.taskloop
+    ! CHECK-SAME: private(@_QFtestEsum_firstprivate_i32 %[[DECLARE_SUM]]#0 -> %arg0, @_QFtestEi_private_i32 %[[DECLARE_I]]#0 -> %arg1, @_QFtestEj_private_i32 %[[DECLARE_J]]#0 -> %arg2 : !fir.ref<i32>, !fir.ref<i32>, !fir.ref<i32>)
+    ! CHECK-LABEL: omp.loop_nest
+    ! CHECK-SAME: (%arg3, %arg4) : i32 = (%c1_i32, %c1_i32_1) to (%c10_i32, %c5_i32) inclusive step (%c1_i32_0, %c1_i32_2) collapse(2)
+    do i = 1, 10
+        do j = 1, 5
+            sum = sum + i + j
+        end do
+    end do
+    !$omp end taskloop
+end subroutine

flang/test/Lower/OpenMP/taskloop-collapse.f90

@@ -0,0 +1,15 @@
+! When lowering Taskloop, it is possible for the TileSizes clause to be lowered, but this is not a supported clause.
+! We should make sure that any use of Tilesizes with Taskloop is correctly rejected by the Semantics.
+! RUN: %python %S/../test_errors.py %s %flang -fopenmp
+
+subroutine test
+    integer :: i, sum
+
+    !ERROR: TILE cannot follow TASKLOOP
+    !ERROR: SIZES clause is not allowed on the TASKLOOP directive
+    !$omp taskloop tile sizes(2)
+    do i=1,10
+        sum = sum + i
+    end do
+    !$omp end taskloop
+end subroutine