Add more tests for DAG CSE

Author: bowenszhu

test/cse.jl

@@ -18,10 +18,31 @@ end
     @test length(sorted_nodes) == 3
     @test isequal(sorted_nodes[1].rhs, a + b)
     @test isequal(sin(sorted_nodes[1].lhs), sorted_nodes[2].rhs)
+
     expr = (a + b)^(a + b)
     sorted_nodes = topological_sort(expr)
     @test length(sorted_nodes) == 2
     @test isequal(sorted_nodes[1].rhs, a + b)
     ab_node = sorted_nodes[1].lhs
     @test isequal(ab_node^ab_node, sorted_nodes[2].rhs)
+    let_expr = cse(expr)
+    @test length(let_expr.pairs) == 1
+    @test isequal(let_expr.pairs[1].rhs, a + b)
+    corresponding_sym = let_expr.pairs[1].lhs
+    @test isequal(let_expr.body, corresponding_sym^corresponding_sym)
+
+    expr = a + b
+    sorted_nodes = topological_sort(expr)
+    @test length(sorted_nodes) == 1
+    @test isequal(sorted_nodes[1].rhs, a + b)
+    let_expr = cse(expr)
+    @test isempty(let_expr.pairs)
+    @test isequal(let_expr.body, a + b)
+    
+    expr = a
+    sorted_nodes = topological_sort(expr)
+    @test isempty(sorted_nodes)
+    let_expr = cse(expr)
+    @test isempty(let_expr.pairs)
+    @test isequal(let_expr.body, a)
 end