[mlir][OpenMP] omp.parallel side effects

Add `NoSideEffects` trait to omp.parallel operation.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D130657

mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td

@@ -125,7 +125,7 @@ def ParallelOp : OpenMP_Op<"parallel", [
   }];
 }
 
-def TerminatorOp : OpenMP_Op<"terminator", [Terminator]> {
+def TerminatorOp : OpenMP_Op<"terminator", [Terminator, NoSideEffect]> {
   let summary = "terminator for OpenMP regions";
   let description = [{
     A terminator operation for regions that appear in the body of OpenMP

mlir/test/Dialect/OpenMP/canonicalize.mlir

@@ -72,3 +72,57 @@ func.func @update_unnecessary_computations(%x: memref<i32>) {
 // CHECK-LABEL: func.func @update_unnecessary_computations
 // CHECK-NOT: omp.atomic.update
 // CHECK: omp.atomic.write
+
+// -----
+
+// CHECK-LABEL: func.func @parallel_empty
+func.func @parallel_empty() {
+  omp.parallel {}
+  return
+}
+
+// CHECK-NOT: omp.parallel
+
+// -----
+
+// CHECK-LABEL: func.func @parallel_only_terminator
+func.func @parallel_only_terminator() {
+  omp.parallel {
+    omp.terminator
+  }
+  return
+}
+
+// CHECK-NOT: omp.parallel
+// CHECK-NOT: omp.terminator
+
+// -----
+
+// CHECK-LABEL: func.func @parallel_no_side_effects
+func.func @parallel_no_side_effects(%a: i32, %b: i32) {
+  omp.parallel {
+    %x = arith.addi %a, %b : i32
+    omp.terminator
+  }
+  return
+}
+
+// CHECK-NOT: omp.parallel
+// CHECK-NOT: omp.terminator
+
+// -----
+
+// CHECK-LABEL: func.func @parallel_maybe_side_effects
+func.func @parallel_maybe_side_effects(%a: i32, %b: i32) {
+  omp.parallel {
+    func.call @foo() : () -> ()
+    omp.terminator
+  }
+  return
+}
+
+func.func private @foo() -> () 
+
+// CHECK: omp.parallel
+// CHECK: func.call @foo() : () -> ()
+// CHECK: omp.terminator