Implements v128.const and adds support for vector value type. (#556)

This commit implements the v128.const, i32x4.add and i64x2.add in
interpreter mode and this adds support for the vector value types in the
locals and globals.

Notably, the vector type values can be passed and returned by exported functions
as well as host functions via two-uint64 encodings as described in #484 (comment).

Note: implementation of these instructions on JIT will be done in subsequent PR.

part of #484

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/wasm/module_test.go

@@ -732,7 +732,7 @@ func TestModule_validateExports(t *testing.T) {
 	}
 }
 
-func TestModule_buildGlobalInstances(t *testing.T) {
+func TestModule_buildGlobals(t *testing.T) {
 	m := Module{GlobalSection: []*Global{
 		{
 			Type: &GlobalType{Mutable: true, ValType: ValueTypeF64},
@@ -744,17 +744,27 @@ func TestModule_buildGlobalInstances(t *testing.T) {
 			Init: &ConstantExpression{Opcode: OpcodeI32Const,
 				Data: leb128.EncodeInt32(math.MaxInt32)},
 		},
+		{
+			Type: &GlobalType{Mutable: false, ValType: ValueTypeV128},
+			Init: &ConstantExpression{Opcode: OpcodeVecV128Const,
+				Data: []byte{
+					1, 0, 0, 0, 0, 0, 0, 0,
+					2, 0, 0, 0, 0, 0, 0, 0,
+				},
+			},
+		},
 	}}
 
 	globals := m.buildGlobals(nil)
 	expectedGlobals := []*GlobalInstance{
 		{Type: &GlobalType{ValType: ValueTypeF64, Mutable: true}, Val: api.EncodeF64(math.MaxFloat64)},
 		{Type: &GlobalType{ValType: ValueTypeI32, Mutable: false}, Val: math.MaxInt32},
+		{Type: &GlobalType{ValType: ValueTypeV128, Mutable: false}, Val: 0x1, ValHi: 0x2},
 	}
 	require.Equal(t, expectedGlobals, globals)
 }
 
-func TestModule_buildFunctionInstances(t *testing.T) {
+func TestModule_buildFunctions(t *testing.T) {
 	nopCode := &Code{nil, []byte{OpcodeEnd}}
 	m := Module{
 		TypeSection:   []*FunctionType{{}},