func (p *Profile) ShowFrom(showFrom *regexp.Regexp) (matched bool) {
	if showFrom == nil {
		return false
	}
	// showFromLocs stores location IDs that matched ShowFrom.
	showFromLocs := make(map[uint64]bool)
	// Apply to locations.
	for _, loc := range p.Location {
		if filterShowFromLocation(loc, showFrom) {
			showFromLocs[loc.ID] = true
			matched = true
		}
	}
	// For all samples, strip locations after the highest matching one.