Merge pull request #626 from nspcc-dev/feature/switch

compiler: implement switch statement support

Implements 1 & 2 from #628.

pkg/compiler/codegen.go

@@ -114,8 +114,7 @@ func (c *codegen) emitStoreLocal(pos int) {
 	}
 
 	emitInt(c.prog.BinWriter, int64(pos))
-	emitInt(c.prog.BinWriter, 2)
-	emitOpcode(c.prog.BinWriter, opcode.ROLL)
+	emitOpcode(c.prog.BinWriter, opcode.ROT)
 	emitOpcode(c.prog.BinWriter, opcode.SETITEM)
 }
 
@@ -337,6 +336,44 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		c.setLabel(lElseEnd)
 		return nil
 
+	case *ast.SwitchStmt:
+		// fallthrough is not supported
+		ast.Walk(c, n.Tag)
+
+		eqOpcode := c.getEqualityOpcode(n.Tag)
+		switchEnd := c.newLabel()
+
+		for i := range n.Body.List {
+			lEnd := c.newLabel()
+			lStart := c.newLabel()
+			cc := n.Body.List[i].(*ast.CaseClause)
+
+			if l := len(cc.List); l != 0 { // if not `default`
+				for j := range cc.List {
+					emitOpcode(c.prog.BinWriter, opcode.DUP)
+					ast.Walk(c, cc.List[j])
+					emitOpcode(c.prog.BinWriter, eqOpcode)
+					if j == l-1 {
+						emitJmp(c.prog.BinWriter, opcode.JMPIFNOT, int16(lEnd))
+					} else {
+						emitJmp(c.prog.BinWriter, opcode.JMPIF, int16(lStart))
+					}
+				}
+			}
+
+			c.setLabel(lStart)
+			for _, stmt := range cc.Body {
+				ast.Walk(c, stmt)
+			}
+			emitJmp(c.prog.BinWriter, opcode.JMP, int16(switchEnd))
+			c.setLabel(lEnd)
+		}
+
+		c.setLabel(switchEnd)
+		emitOpcode(c.prog.BinWriter, opcode.DROP)
+
+		return nil
+
 	case *ast.BasicLit:
 		c.emitLoadConst(c.typeInfo.Types[n])
 		return nil
@@ -431,11 +468,8 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 				}
 			case n.Op == token.EQL:
 				// VM has separate opcodes for number and string equality
-				if isStringType(c.typeInfo.Types[n.X].Type) {
-					emitOpcode(c.prog.BinWriter, opcode.EQUAL)
-				} else {
-					emitOpcode(c.prog.BinWriter, opcode.NUMEQUAL)
-				}
+				op := c.getEqualityOpcode(n.X)
+				emitOpcode(c.prog.BinWriter, op)
 			case n.Op == token.NEQ:
 				// VM has separate opcodes for number and string equality
 				if isStringType(c.typeInfo.Types[n.X].Type) {
@@ -657,6 +691,15 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 	return c
 }
 
+func (c *codegen) getEqualityOpcode(expr ast.Expr) opcode.Opcode {
+	t, ok := c.typeInfo.Types[expr].Type.Underlying().(*types.Basic)
+	if ok && t.Info()&types.IsNumeric != 0 {
+		return opcode.NUMEQUAL
+	}
+
+	return opcode.EQUAL
+}
+
 // getByteArray returns byte array value from constant expr.
 // Only literals are supported.
 func (c *codegen) getByteArray(expr ast.Expr) []byte {

pkg/compiler/switch_test.go

@@ -0,0 +1,138 @@
+package compiler_test
+
+import (
+	"math/big"
+	"testing"
+)
+
+var switchTestCases = []testCase{
+	{
+		"simple switch success",
+		`package main
+		func Main() int {
+			a := 5
+			switch a {
+			case 5: return 2
+			}
+			return 1
+		}`,
+		big.NewInt(2),
+	},
+	{
+		"simple switch fail",
+		`package main
+		func Main() int {
+			a := 6
+			switch a {
+			case 5:
+				return 2
+			}
+			return 1
+		}`,
+		big.NewInt(1),
+	},
+	{
+		"multiple cases success",
+		`package main
+		func Main() int {
+			a := 6
+			switch a {
+			case 5: return 2
+			case 6: return 3
+			}
+			return 1
+		}`,
+		big.NewInt(3),
+	},
+	{
+		"multiple cases fail",
+		`package main
+		func Main() int {
+			a := 7
+			switch a {
+			case 5: return 2
+			case 6: return 3
+			}
+			return 1
+		}`,
+		big.NewInt(1),
+	},
+	{
+		"default case",
+		`package main
+		func Main() int {
+			a := 7
+			switch a {
+			case 5: return 2
+			case 6: return 3
+			default: return 4
+			}
+			return 1
+		}`,
+		big.NewInt(4),
+	},
+	{
+		"empty case before default",
+		`package main
+		func Main() int {
+			a := 6
+			switch a {
+			case 5: return 2
+			case 6:
+			default: return 4
+			}
+			return 1
+		}`,
+		big.NewInt(1),
+	},
+	{
+		"expression in case clause",
+		`package main
+		func Main() int {
+			a := 6
+			b := 3
+			switch a {
+			case 5: return 2
+			case b*3-3: return 3
+			}
+			return 1
+		}`,
+		big.NewInt(3),
+	},
+	{
+		"multiple expressions in case",
+		`package main
+		func Main() int {
+			a := 8
+			b := 3
+			switch a {
+			case 5: return 2
+			case b*3-3, 7, 8: return 3
+			}
+			return 1
+		}`,
+		big.NewInt(3),
+	},
+	{
+		"string switch",
+		`package main
+		func Main() int {
+			name := "Valera"
+			switch name {
+			case "Misha": return 2
+			case "Katya", "Dima": return 3
+			case "Lera", "Valer" + "a": return 4
+			}
+			return 1
+		}`,
+		big.NewInt(4),
+	},
+}
+
+func TestSwitch(t *testing.T) {
+	for _, tc := range switchTestCases {
+		t.Run(tc.name, func(t *testing.T) {
+			eval(t, tc.src, tc.result)
+		})
+	}
+}