build: mov deduction for booleans (#341)

Updates #336

tests/fixedbugs/issue336/asm.go

@@ -0,0 +1,38 @@
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	"fmt"
+
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+	. "github.com/mmcloughlin/avo/reg"
+)
+
+func main() {
+	variants := []struct {
+		Size     int
+		Register func() GPVirtual
+		XOR      func(Op, Op)
+	}{
+		{8, GP8L, XORB},
+		{16, GP16, XORW},
+		{32, GP32, XORL},
+		{64, GP64, XORQ},
+	}
+
+	for _, v := range variants {
+		name := fmt.Sprintf("Not%d", v.Size)
+		TEXT(name, NOSPLIT, "func(x bool) bool")
+		Doc(fmt.Sprintf("%s returns the boolean negation of x using a %d-bit intermediate.", name, v.Size))
+		x := v.Register()
+		Load(Param("x"), x)
+		v.XOR(U8(1), x)
+		Store(x.As8L(), ReturnIndex(0))
+		RET()
+	}
+
+	Generate()
+}