Add tagshow/taghide commands to select a subset of tags

internal/driver/commands.go

 	"tagignore": &variable{stringKind, "", "", helpText(
 		"Discard samples with tags in range or matched by regexp",
 		"Discard samples that do include a node with a tag matching this regexp.")},
-
+	"tagshow": &variable{stringKind, "", "", helpText(
+		"Only consider tags matching this regexp",
+		"Discard tags that do not match this regexp")},
+	"taghide": &variable{stringKind, "", "", helpText(
+		"Skip tags matching this regexp",
+		"Discard tags that match this regexp")},
 	// Heap profile options
 	"divide_by": &variable{floatKind, "1", "", helpText(
 		"Ratio to divide all samples before visualization",

internal/driver/driver_focus.go

 	warnNoMatches(tagfocus == nil || tfm, "TagFocus", ui)
 	warnNoMatches(tagignore == nil || tim, "TagIgnore", ui)
 
+	tagshow, err := compileRegexOption("tagshow", v["tagshow"].value, err)
+	taghide, err := compileRegexOption("taghide", v["taghide"].value, err)
+	tns, tnh := prof.FilterTagsByName(tagshow, taghide)
+	warnNoMatches(tagshow == nil || tns, "TagShow", ui)
+	warnNoMatches(tagignore == nil || tnh, "TagHide", ui)
+
 	if prunefrom != nil {
 		prof.PruneFrom(prunefrom)
 	}

profile/filter.go

 	return
 }
 
+// FilterTagsByName filters the tags in a profile and only keeps
+// tags that match show and not hide.
+func (p *Profile) FilterTagsByName(show, hide *regexp.Regexp) (sm, hm bool) {
+	matchShow := func(name string) bool {
+		matchShow := show == nil || show.MatchString(name)
+		matchHide := hide != nil && hide.MatchString(name)
+
+		if matchShow {
+			sm = true
+		}
+		if matchHide {
+			hm = true
+		}
+		return matchShow && !matchHide
+	}
+	for _, s := range p.Sample {
+		for lab := range s.Label {
+			if !matchShow(lab) {
+				delete(s.Label, lab)
+			}
+		}
+		for lab := range s.NumLabel {
+			if !matchShow(lab) {
+				delete(s.NumLabel, lab)
+			}
+		}
+	}
+	return
+}
+
 // matchesName returns whether the location matches the regular
 // expression. It checks any available function names, file names, and
 // mapping object filename.