tests: test functions with random signatures (#216)

Adds a test for function signature memory layout by generating functions with
random signatures. This confirms that the size and offsets computed by
`gotypes` agree with `asmdecl`.

Updates #191 #195

tests/signature/asm.go

@@ -0,0 +1,78 @@
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"go/token"
+	"go/types"
+	"math/rand"
+
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/gotypes"
+	. "github.com/mmcloughlin/avo/reg"
+)
+
+var (
+	seed = flag.Int64("seed", 0, "random seed")
+	num  = flag.Int("num", 32, "number of test functions to generate")
+)
+
+func main() {
+	flag.Parse()
+
+	rand.Seed(*seed)
+
+	for i := 0; i < *num; i++ {
+		name := fmt.Sprintf("Signature%d", i)
+		sig := RandomSignature()
+		SignatureFunction(name, sig)
+	}
+
+	Generate()
+}
+
+func SignatureFunction(name string, sig *types.Signature) {
+	// Declare the function.
+	TEXT(name, 0, sig.String())
+
+	// Write to the results. Otherwise, asmdecl would warn us.
+	regsize := map[int64]Virtual{1: GP8(), 2: GP16(), 4: GP32(), 8: GP64()}
+	rs := sig.Results()
+	for i := 0; i < rs.Len(); i++ {
+		r := rs.At(i)
+		size := Sizes.Sizeof(r.Type())
+		Store(regsize[size], ReturnIndex(i))
+	}
+
+	RET()
+}
+
+func RandomSignature() *types.Signature {
+	p := RandomTuple()
+	r := RandomTuple()
+	return types.NewSignature(nil, p, r, false)
+}
+
+func RandomTuple() *types.Tuple {
+	n := rand.Intn(5)
+	vs := make([]*types.Var, n)
+	for i := 0; i < n; i++ {
+		t := RandomType()
+		vs[i] = types.NewVar(token.NoPos, nil, "", t)
+	}
+	return types.NewTuple(vs...)
+}
+
+func RandomType() types.Type {
+	accept := types.IsInteger | types.IsUnsigned
+	for {
+		t := types.Typ[rand.Intn(len(types.Typ))]
+		info := t.Info()
+		if info != 0 && (info&^accept) == 0 {
+			return t
+		}
+	}
+}