gotypes,build: pointer dereference (#61)

Provides a method on `gotypes.Component` to allow pointer dereference. This will enable `gotypes` helpers to be used with struct pointer arguments, for example.

Updates #53 
Fixes #54

build/global.go

@@ -112,6 +112,9 @@ func Load(src gotypes.Component, dst reg.Register) reg.Register { return ctx.Loa
 // attempt to select the right MOV instruction based on the types involved.
 func Store(src reg.Register, dst gotypes.Component) { ctx.Store(src, dst) }
 
+// Dereference loads a pointer and returns its element type.
+func Dereference(ptr gotypes.Component) gotypes.Component { return ctx.Dereference(ptr) }
+
 // Doc sets documentation comment lines for the currently active function.
 func Doc(lines ...string) { ctx.Doc(lines...) }
 

build/pseudo.go

@@ -54,6 +54,13 @@ func (c *Context) Store(src reg.Register, dst gotypes.Component) {
 	c.mov(src, b.Addr, int(src.Bytes()), int(gotypes.Sizes.Sizeof(b.Type)), b.Type)
 }
 
+// Dereference loads a pointer and returns its element type.
+func (c *Context) Dereference(ptr gotypes.Component) gotypes.Component {
+	r := c.GP64()
+	c.Load(ptr, r)
+	return ptr.Dereference(r)
+}
+
 // ConstData builds a static data section containing just the given constant.
 func (c *Context) ConstData(name string, v operand.Constant) operand.Mem {
 	g := c.StaticGlobal(name)

examples/args/args.s

@@ -109,3 +109,10 @@ TEXT ·FieldComplex128Real(SB), NOSPLIT, $0-184
 	MOVSD s_Complex128_real+160(FP), X0
 	MOVSD X0, ret+176(FP)
 	RET
+
+// func DereferenceFloat32(s *Struct) float32
+TEXT ·DereferenceFloat32(SB), NOSPLIT, $0-12
+	MOVQ  s+0(FP), AX
+	MOVSS 16(AX), X0
+	MOVSS X0, ret+8(FP)
+	RET

examples/args/args_test.go

@@ -1,6 +1,7 @@
 package args
 
 import (
+	"math"
 	"testing"
 	"testing/quick"
 )
@@ -36,3 +37,12 @@ func TestFunctionsEqual(t *testing.T) {
 		}
 	}
 }
+
+func TestDereferenceFloat32(t *testing.T) {
+	expect := float32(math.Pi)
+	s := Struct{Float32: expect}
+	got := DereferenceFloat32(&s)
+	if got != expect {
+		t.Errorf("DereferenceFloat32(%v) = %v; expect %v", s, got, expect)
+	}
+}

examples/args/asm.go

@@ -99,5 +99,11 @@ func main() {
 	Store(c128r, ReturnIndex(0))
 	RET()
 
+	TEXT("DereferenceFloat32", NOSPLIT, "func(s *Struct) float32")
+	s := Dereference(Param("s"))
+	f := Load(s.Field("Float32"), XMM())
+	Store(f, ReturnIndex(0))
+
+	RET()
 	Generate()
 }

examples/args/stub.go

@@ -37,3 +37,5 @@ func FieldArrayOneC(s Struct) uint16
 func FieldComplex64Imag(s Struct) float32
 
 func FieldComplex128Real(s Struct) float64
+
+func DereferenceFloat32(s *Struct) float32

gotypes/components.go

@@ -7,6 +7,8 @@ import (
 	"go/types"
 	"strconv"
 
+	"github.com/mmcloughlin/avo/reg"
+
 	"github.com/mmcloughlin/avo/operand"
 )
 
@@ -27,6 +29,7 @@ type Component interface {
 	// resolution time.
 	Resolve() (*Basic, error)
 
+	Dereference(r reg.Register) Component // dereference a pointer
 	Base() Component                      // base pointer of a string or slice
 	Len() Component                       // length of a string or slice
 	Cap() Component                       // capacity of a slice
@@ -47,6 +50,7 @@ func errorf(format string, args ...interface{}) Component {
 
 func (c componenterr) Error() string                        { return string(c) }
 func (c componenterr) Resolve() (*Basic, error)             { return nil, c }
+func (c componenterr) Dereference(r reg.Register) Component { return c }
 func (c componenterr) Base() Component                      { return c }
 func (c componenterr) Len() Component                       { return c }
 func (c componenterr) Cap() Component                       { return c }
@@ -56,17 +60,15 @@ func (c componenterr) Index(int) Component      { return c }
 func (c componenterr) Field(string) Component               { return c }
 
 type component struct {
-	name   string
 	typ  types.Type
-	offset int
+	addr operand.Mem
 }
 
-// NewComponent builds a component for the named type at the given memory offset.
-func NewComponent(name string, t types.Type, offset int) Component {
+// NewComponent builds a component for the named type at the given address.
+func NewComponent(t types.Type, addr operand.Mem) Component {
 	return &component{
-		name:   name,
 		typ:  t,
-		offset: offset,
+		addr: addr,
 	}
 }
 
@@ -76,11 +78,19 @@ func (c *component) Resolve() (*Basic, error) {
 		return nil, errors.New("component is not primitive")
 	}
 	return &Basic{
-		Addr: operand.NewParamAddr(c.name, c.offset),
+		Addr: c.addr,
 		Type: b,
 	}, nil
 }
 
+func (c *component) Dereference(r reg.Register) Component {
+	p, ok := c.typ.Underlying().(*types.Pointer)
+	if !ok {
+		return errorf("not pointer type")
+	}
+	return NewComponent(p.Elem(), operand.Mem{Base: r})
+}
+
 // Reference: https://github.com/golang/go/blob/50bd1c4d4eb4fac8ddeb5f063c099daccfb71b26/src/reflect/value.go#L1800-L1804
 //
 //	type SliceHeader struct {
@@ -194,8 +204,10 @@ func (c *component) Field(n string) Component {
 
 func (c *component) sub(suffix string, offset int, t types.Type) *component {
 	s := *c
-	s.name += suffix
-	s.offset += offset
+	if s.addr.Symbol.Name != "" {
+		s.addr.Symbol.Name += suffix
+	}
+	s.addr = s.addr.Offset(offset)
 	s.typ = t
 	return &s
 }

gotypes/components_test.go

@@ -2,7 +2,12 @@ package gotypes
 
 import (
 	"go/types"
+	"strings"
 	"testing"
+
+	"github.com/mmcloughlin/avo/reg"
+
+	"github.com/mmcloughlin/avo/operand"
 )
 
 func TestBasicKindsArePrimitive(t *testing.T) {
@@ -33,8 +38,61 @@ func TestPointersArePrimitive(t *testing.T) {
 }
 
 func AssertPrimitive(t *testing.T, typ types.Type) {
-	c := NewComponent("primitive", typ, 0)
+	c := NewComponent(typ, operand.NewParamAddr("primitive", 0))
 	if _, err := c.Resolve(); err != nil {
 		t.Errorf("expected type %s to be primitive: got error '%s'", typ, err)
 	}
 }
+
+func TestComponentErrors(t *testing.T) {
+	comp := NewComponent(types.Typ[types.Uint32], operand.Mem{})
+	cases := []struct {
+		Component      Component
+		ErrorSubstring string
+	}{
+		{comp.Base(), "only slices and strings"},
+		{comp.Len(), "only slices and strings"},
+		{comp.Cap(), "only slices have"},
+		{comp.Real(), "only complex"},
+		{comp.Imag(), "only complex"},
+		{comp.Index(42), "not array type"},
+		{comp.Field("a"), "not struct type"},
+		{comp.Dereference(reg.R12), "not pointer type"},
+	}
+	for _, c := range cases {
+		_, err := c.Component.Resolve()
+		if err == nil {
+			t.Fatal("expected error")
+		}
+		if !strings.Contains(err.Error(), c.ErrorSubstring) {
+			t.Fatalf("error message %q; expected substring %q", err.Error(), c.ErrorSubstring)
+		}
+	}
+}
+
+func TestComponentErrorChaining(t *testing.T) {
+	// Build a component with an error.
+	comp := NewComponent(types.Typ[types.Uint32], operand.Mem{}).Index(3)
+	_, expect := comp.Resolve()
+	if expect == nil {
+		t.Fatal("expected error")
+	}
+
+	// Confirm that the error is preserved through chaining operations.
+	cases := []Component{
+		comp.Dereference(reg.R13),
+		comp.Base(),
+		comp.Len(),
+		comp.Cap(),
+		comp.Real(),
+		comp.Imag(),
+		comp.Index(42),
+		comp.Field("field"),
+	}
+	for _, c := range cases {
+		_, err := c.Resolve()
+		if err != expect {
+			t.Fatal("chaining should preserve error")
+		}
+	}
+}

gotypes/signature.go

@@ -7,6 +7,8 @@ import (
 	"go/token"
 	"go/types"
 	"strconv"
+
+	"github.com/mmcloughlin/avo/operand"
 )
 
 // Signature represents a Go function signature.
@@ -136,7 +138,8 @@ func newTuple(t *types.Tuple, offsets []int64, size int64, defaultprefix string)
 				name += strconv.Itoa(i)
 			}
 		}
-		c := NewComponent(name, v.Type(), int(offsets[i]))
+		addr := operand.NewParamAddr(name, int(offsets[i]))
+		c := NewComponent(v.Type(), addr)
 		tuple.components = append(tuple.components, c)
 		if v.Name() != "" {
 			tuple.byname[v.Name()] = c