func filterShowFromLocation(loc *Location, showFrom *regexp.Regexp) bool {
	if m := loc.Mapping; m != nil && showFrom.MatchString(m.File) {
		return true
	}
	if i := loc.lastMatchedLineIndex(showFrom); i >= 0 {
		loc.Line = loc.Line[:i+1]
		return true
	}
	return false
}
filterShowFromLocation tests a showFrom regex against a location, removes
lines after the last match and returns whether a match was found. If the
mapping is matched, then all lines are kept.
package profile
import "regexp"
func (p *Profile) FilterSamplesByName(focus, ignore, hide, show *regexp.Regexp) (fm, im, hm, hnm bool) {
	focusOrIgnore := make(map[uint64]bool)
	hidden := make(map[uint64]bool)
	for _, l := range p.Location {
		if ignore != nil && l.matchesName(ignore) {
			im = true
			focusOrIgnore[l.ID] = false
		} else if focus == nil || l.matchesName(focus) {
			fm = true
			focusOrIgnore[l.ID] = true
		}
		if hide != nil && l.matchesName(hide) {
			hm = true
			l.Line = l.unmatchedLines(hide)
			if len(l.Line) == 0 {
				hidden[l.ID] = true
			}
		}
		if show != nil {
			l.Line = l.matchedLines(show)
			if len(l.Line) == 0 {
				hidden[l.ID] = true
			} else {
				hnm = true
			}
		}
	}
	s := make([]*Sample, 0, len(p.Sample))
	for _, sample := range p.Sample {
		if focusedAndNotIgnored(sample.Location, focusOrIgnore) {
			if len(hidden) > 0 {
				var locs []*Location
				for _, loc := range sample.Location {
					if !hidden[loc.ID] {
						locs = append(locs, loc)
					}
				}
				if len(locs) == 0 {
					continue
				}
				sample.Location = locs
			}
			s = append(s, sample)
		}
	}
	p.Sample = s
	return
}
func (p *Profile) ShowFrom(showFrom *regexp.Regexp) (matched bool) {
	if showFrom == nil {
		return false
	}
	showFromLocs := make(map[uint64]bool)
	for _, loc := range p.Location {
		if filterShowFromLocation(loc, showFrom) {
			showFromLocs[loc.ID] = true
			matched = true
		}
	}
	s := make([]*Sample, 0, len(p.Sample))
	for _, sample := range p.Sample {
		for i := len(sample.Location) - 1; i >= 0; i-- {
			if showFromLocs[sample.Location[i].ID] {
				sample.Location = sample.Location[:i+1]
				s = append(s, sample)
				break
			}
		}
	}
	p.Sample = s
	return matched
}