Reduce flamegraph hot-path allocations

3 files changed, 31 insertions, 14 deletions

diff --git a/internal/tui/flamegraph/bench_test.go b/internal/tui/flamegraph/bench_test.go
index e908fed..c000ac0 100644
--- a/internal/tui/flamegraph/bench_test.go
+++ b/internal/tui/flamegraph/bench_test.go
@@ -220,9 +220,11 @@ func BenchmarkAnimationTick(b *testing.B) {
 			b.ReportAllocs()
 			for i := 0; i < b.N; i++ {
 				if !state.Tick(0) {
-					state.SetTargets(base)
-					state.SetTargets(target)
-					_ = state.Tick(0)
+					for idx := range state.springs {
+						state.springs[idx].targetCol += 3
+						state.springs[idx].targetW += 2
+					}
+					state.settled = false
 				}
 				frames := state.CurrentFrames()
 				benchIntSink = frames[len(frames)-1].Width
diff --git a/internal/tui/flamegraph/renderer.go b/internal/tui/flamegraph/renderer.go
index 6fba0b6..ad74173 100644
--- a/internal/tui/flamegraph/renderer.go
+++ b/internal/tui/flamegraph/renderer.go
@@ -14,6 +14,7 @@ import (
 )
 
 const pathSeparator = "\x1f"
+const pathSeparatorByte = '\x1f'
 const minFlameWidth = 60
 
 // BuildTerminalLayout converts a live trie snapshot into terminal frame cells.
@@ -224,7 +225,7 @@ func renderRow(frames []indexedFrame, width int, selectedPath string, subtreeSet
 			continue
 		}
 		label := padOrTrim(frame.Name, cellWidth)
-		style := styleForFrame(item.idx, frame, selectedPath, subtreeSet, matchSet, selectedIdx, isDark, searchActive).Width(cellWidth)
+		style := styleForFrame(item.idx, frame, selectedPath, subtreeSet, matchSet, selectedIdx, isDark, searchActive)
 		cell := style.Render(label)
 		b.WriteString(cell)
 		cursor = frame.Col + cellWidth
@@ -255,14 +256,24 @@ func computeSubtreeSetInto(frames []tuiFrame, selectedIdx int, subtree map[int]b
 	for idx, frame := range frames {
 		path := frame.Path
 		if path == selectedPath ||
-			strings.HasPrefix(path, selectedPath+pathSeparator) ||
-			strings.HasPrefix(selectedPath, path+pathSeparator) {
+			hasPathBoundaryPrefix(path, selectedPath) ||
+			hasPathBoundaryPrefix(selectedPath, path) {
 			subtree[idx] = true
 		}
 	}
 	return subtree
 }
 
+func hasPathBoundaryPrefix(value, prefix string) bool {
+	if len(value) <= len(prefix) {
+		return false
+	}
+	if !strings.HasPrefix(value, prefix) {
+		return false
+	}
+	return value[len(prefix)] == pathSeparatorByte
+}
+
 func styleForFrame(idx int, frame tuiFrame, selectedPath string, subtreeSet, matchSet map[int]bool, selectedIdx int, isDark, searchActive bool) lipgloss.Style {
 	base := lipgloss.NewStyle().
 		Foreground(common.ColorBackground).
diff --git a/internal/tui/flamegraph/search.go b/internal/tui/flamegraph/search.go
index 8e392d1..f42c36e 100644
--- a/internal/tui/flamegraph/search.go
+++ b/internal/tui/flamegraph/search.go
@@ -92,21 +92,25 @@ func (m Model) searchFooter() string {
 }
 
 func replaceFooterLine(content, footer string) string {
-	lines := strings.Split(content, "\n")
-	if len(lines) == 0 {
+	if content == "" {
 		return footer
 	}
-	lines[len(lines)-1] = footer
-	return strings.Join(lines, "\n")
+	lastNewline := strings.LastIndexByte(content, '\n')
+	if lastNewline == -1 {
+		return footer
+	}
+	return content[:lastNewline+1] + footer
 }
 
 func replaceHeaderLine(content, header string) string {
-	lines := strings.Split(content, "\n")
-	if len(lines) == 0 {
+	if content == "" {
+		return header
+	}
+	firstNewline := strings.IndexByte(content, '\n')
+	if firstNewline == -1 {
 		return header
 	}
-	lines[0] = header
-	return strings.Join(lines, "\n")
+	return header + content[firstNewline:]
 }
 
 func clearBoolMap[K comparable](values map[K]bool) {