6. Align directive

Go asm supports the PCALIGN directive, which indicates that the next instruction should be aligned
to a specified boundary by padding with NOOP instruction. The alignment value supported on arm64
must be a power of 2 and in the range of [8, 2048].

Examples:

	PCALIGN $16
	MOVD $2, R0          // This instruction is aligned with 16 bytes.
	PCALIGN $1024
	MOVD $3, R1          // This instruction is aligned with 1024 bytes.

	f := stdSizes.Sizeof
	if conf.Sizes != nil {
		f = conf.Sizes.Sizeof
	}
	return f(T)
}

// align returns the smallest y >= x such that y % a == 0.
// a must be within 1 and 8 and it must be a power of 2.
// The result may be negative due to overflow.
func align(x, a int64) int64 {
	assert(x >= 0 && 1 <= a && a <= 8 && a&(a-1) == 0)
	return (x + a - 1) &^ (a - 1)

	// computed with:
	//
	// 	Algorithm 2: Algorithm to select the number of fractional bits
	// 	and the scaled approximate reciprocal in the case of unsigned
	// 	integers.
	//
	// 	if d is a power of two then
	// 		Let F ← log₂(d) and c = 1.
	// 	else
	// 		Let F ← N + L where L is the smallest integer
	// 		such that d ≤ (2^(N+L) mod d) + 2^L.
	// 	end if
	//

// this feature, we should consider/propose a better way to accomplish it.
func AdjustStartingHeap(requestedHeapGoal uint64) {
	logHeapTweaks := Debug.GCAdjust == 1
	mp := runtime.GOMAXPROCS(0)
	gcConcurrency := Flag.LowerC

	const (
		goal   = "/gc/heap/goal:bytes"
		count  = "/gc/cycles/total:gc-cycles"
		allocs = "/gc/heap/allocs:bytes"
		frees  = "/gc/heap/frees:bytes"
	)