Prune profile info to only keep hot functions.

collects/typed-racket/optimizer/tool/profiling.rkt

@@ -6,6 +6,7 @@
 
 (provide generate-profile
          node-source node-line node-col node-pos node-span
+         prune-profile
          (all-from-out profile/analyzer))
 
 (define ((mk accessor) node)
@@ -41,3 +42,27 @@
     (equal? (and src (srcloc-source src)) res-mpi))
   (define orig-profile (analyze-samples snapshots))
   (filter right-file? (profile-nodes orig-profile)))
+
+
+;; In some cases, we only want to consider "hot" functions for further
+;; analysis. `prune-profile' prunes non-hot functions from the profile.
+;; To determine what is hot, we pick, in order, the hottest functions
+;; (by self time. total time could be used, but may not work as well)
+;; until our picks cover `total-relative-time-cutoff' (e.g. half) of
+;; the total running time.
+(define total-relative-time-cutoff .95) ; picked arbitrarily, subject to tweaking
+(define (prune-profile profile)
+  (define total-time   (profile-total-time profile))
+  (define target-time  (* total-time total-relative-time-cutoff))
+  (define sorted-nodes (sort (profile-nodes profile) > #:key node-self))
+  (define top-nodes
+    (let loop ([nodes sorted-nodes] [res '()] [sum 0])
+      ;; The last function we pick can go beyond the target.
+      ;; O/w, if we had a single function, taking up 100% time, it would
+      ;; be discarded.
+      (cond [(or (null? nodes) (> sum target-time))
+             res]
+            [else
+             (define h (car nodes))
+             (loop (cdr nodes) (cons h res) (+ sum (node-self h)))])))
+  top-nodes)