compiler: do not allocate static slot for constants

Their value is known at compile time.

pkg/compiler/analysis.go

@@ -109,8 +109,13 @@ func countGlobals(f ast.Node) (i int) {
 			return false
 		// After skipping all funcDecls we are sure that each value spec
 		// is a global declared variable or constant.
-		case *ast.ValueSpec:
+		case *ast.GenDecl:
-			i += len(n.Names)
+			if n.Tok == token.VAR {
+				for _, s := range n.Specs {
+					i += len(s.(*ast.ValueSpec).Names)
+				}
+			}
+			return false
 		}
 		return true
 	})

pkg/compiler/global_test.go

@@ -1,6 +1,7 @@
 package compiler_test
 
 import (
+	"bytes"
 	"fmt"
 	"math/big"
 	"strings"
@@ -238,3 +239,19 @@ func TestMultipleFuncSameName(t *testing.T) {
 		eval(t, src, big.NewInt(42))
 	})
 }
+
+func TestConstDontUseSlots(t *testing.T) {
+	const count = 256
+	buf := bytes.NewBufferString("package foo\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("const n%d = 1\n", i))
+	}
+	buf.WriteString("func Main() int { sum := 0\n")
+	for i := 0; i < count; i++ {
+		buf.WriteString(fmt.Sprintf("sum += n%d\n", i))
+	}
+	buf.WriteString("return sum }")
+
+	src := buf.String()
+	eval(t, src, big.NewInt(count))
+}