tests/alloc/gp8: allocator test using all 8-bit registers (#102)

Updates #43

tests/alloc/gp8/asm.go

@@ -0,0 +1,39 @@
+// +build ignore
+
+package main
+
+import (
+	"strconv"
+
+	. "github.com/mmcloughlin/avo/build"
+	. "github.com/mmcloughlin/avo/operand"
+	. "github.com/mmcloughlin/avo/reg"
+)
+
+func main() {
+	// n is the number of 8-bit registers to use.
+	// 15 low-byte registers (excluding SP)
+	// 4 high-byte registers AH,BH,CH,DH
+	const n = 19
+
+	TEXT("GP8", NOSPLIT, "func() uint8")
+	Doc("GP8 returns the sum 1+2+...+" + strconv.Itoa(n) + " using " + strconv.Itoa(n) + " distinct 8-bit registers.")
+
+	// Allocate registers and initialize.
+	x := make([]Register, n)
+	for i := 0; i < n; i++ {
+		x[i] = GP8()
+		MOVB(U8(i+1), x[i])
+	}
+
+	// Sum them up.
+	for i := 1; i < n; i++ {
+		ADDB(x[i], x[0])
+	}
+
+	// Return.
+	Store(x[0], ReturnIndex(0))
+	RET()
+
+	Generate()
+}