compiler: support nil checks

pkg/compiler/nilcheck_test.go

@@ -0,0 +1,55 @@
+package compiler_test
+
+import (
+	"math/big"
+	"testing"
+)
+
+var nilTestCases = []testCase{
+	{
+		"nil check positive right",
+		`
+		package foo
+		func Main() int {
+			var t interface{}
+			if t == nil {
+				return 1
+			}
+			return 2
+		}
+		`,
+		big.NewInt(1),
+	},
+	{
+		"nil check negative right",
+		`
+		package foo
+		func Main() int {
+			t := []byte{}
+			if t == nil {
+				return 1
+			}
+			return 2
+		}
+		`,
+		big.NewInt(2),
+	},
+	{
+		"nil check positive left",
+		`
+		package foo
+		func Main() int {
+			var t interface{}
+			if nil == t {
+				return 1
+			}
+			return 2
+		}
+		`,
+		big.NewInt(1),
+	},
+}
+
+func TestNil(t *testing.T) {
+	runTestCases(t, nilTestCases)
+}