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

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