T-298: perf(quartet_concordance): hoist buffer resize outside split loop

dev/benchmarks/bench_quartet_concordance.R

@@ -0,0 +1,49 @@
+# Benchmark and profile quartet_concordance
+# T-298: Profile flat array vs NumericMatrix, int vs double
+#
+# Usage: Rscript dev/benchmarks/bench_quartet_concordance.R
+# Or interactively for profvis output.
+#
+# Install from source first (tarball build per AGENTS.md).
+
+library(TreeSearch)
+
+set.seed(42)
+
+make_inputs <- function(n_taxa, n_splits, n_chars, n_states = 4) {
+  splits <- matrix(sample(c(TRUE, FALSE), n_taxa * n_splits, replace = TRUE),
+                   nrow = n_taxa, ncol = n_splits)
+  # IntegerMatrix with NAs (~5% missing)
+  chars <- matrix(sample(c(0:(n_states - 1), NA_integer_),
+                         n_taxa * n_chars, replace = TRUE, prob = c(rep(0.95/n_states, n_states), 0.05)),
+                  nrow = n_taxa, ncol = n_chars)
+  list(splits = splits, chars = chars)
+}
+
+sizes <- list(
+  small  = list(n_taxa = 25,  n_splits = 23,  n_chars = 50),
+  medium = list(n_taxa = 100, n_splits = 98,  n_chars = 200),
+  large  = list(n_taxa = 300, n_splits = 298, n_chars = 400)
+)
+
+cat("=== Timing quartet_concordance ===\n")
+for (nm in names(sizes)) {
+  sz <- sizes[[nm]]
+  inp <- make_inputs(sz$n_taxa, sz$n_splits, sz$n_chars)
+  t <- system.time(
+    for (i in seq_len(10)) TreeSearch:::quartet_concordance(inp$splits, inp$chars)
+  )
+  cat(sprintf("%-8s (%3d taxa, %3d splits, %3d chars): %.3fs / call\n",
+              nm, sz$n_taxa, sz$n_splits, sz$n_chars, t[["elapsed"]] / 10))
+}
+
+# --- profvis profile of the medium case ---
+if (requireNamespace("profvis", quietly = TRUE)) {
+  inp <- make_inputs(100, 98, 200)
+  p <- profvis::profvis({
+    for (i in seq_len(50)) TreeSearch:::quartet_concordance(inp$splits, inp$chars)
+  })
+  print(p)
+} else {
+  message("Install profvis for flame graph: install.packages('profvis')")
+}

src/quartet_concordance.cpp

@@ -18,22 +18,28 @@ List quartet_concordance(const LogicalMatrix splits, const IntegerMatrix charact
   active_states.reserve(32);
 
   for (int c = 0; c < n_chars; ++c) {
-    // Cache character column for memory locality
+    // Cache character column and find max state in one pass
     std::vector<int> char_col(n_taxa);
-    for (int t = 0; t < n_taxa; ++t) char_col[t] = characters(t, c);
+    int max_state = 0;
+    for (int t = 0; t < n_taxa; ++t) {
+      int state = characters(t, c);
+      char_col[t] = state;
+      if (!IntegerVector::is_na(state) && state > max_state) max_state = state;
+    }
+    // Hoist resize outside split loop: only reallocate when a new character
+    // has states beyond the current buffer capacity.
+    if (max_state >= (int)n0.size()) {
+      n0.resize(max_state + 1, 0);
+      n1.resize(max_state + 1, 0);
+    }
 
     for (int s = 0; s < n_splits; ++s) {
       active_states.clear();
 
       for (int t = 0; t < n_taxa; ++t) {
         int state = char_col[t];
         if (IntegerVector::is_na(state)) continue;
-
-        if (state >= (int)n0.size()) {
-          n0.resize(state + 1, 0);
-          n1.resize(state + 1, 0);
-        }
-
+
         if (n0[state] == 0 && n1[state] == 0) {
           active_states.push_back(state);
         }