From f8b8c92b407d5ebeee4d6b015f93b547abf25527 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Mon, 3 Jun 2024 11:46:19 -0700
Subject: [PATCH] ILP firstGeq WIP

---
 VersionedMap.cpp | 130 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 92 insertions(+), 38 deletions(-)

diff --git a/VersionedMap.cpp b/VersionedMap.cpp
index bc5657e..dffa09c 100644
--- a/VersionedMap.cpp
+++ b/VersionedMap.cpp
@@ -1229,53 +1229,107 @@ bool geq(const VersionedMap::Iterator::VersionedMutation &m,
 void VersionedMap::Impl::firstGeq(const weaselab::VersionedMap::Key *key,
                                   const int64_t *version, Iterator *iterator,
                                   int count) const {
-  // TODO ILP!
-  auto handle = roots.getThreadSafeHandle();
-  for (int i = 0; i < count; ++i) {
 
-    uint32_t root;
-    if (iterator[i].impl != nullptr) {
-      root = iterator[i].impl->version == version[i]
-                 ? iterator[i].impl->finger.root()
-                 : handle.rootForVersion(version[i]);
-      iterator[i].impl->~Impl();
-      new (iterator[i].impl) Iterator::Impl();
-    } else {
-      root = handle.rootForVersion(version[i]);
-      iterator[i].impl =
-          new (safe_malloc(sizeof(Iterator::Impl))) Iterator::Impl();
-    }
-    Finger &finger = iterator[i].impl->finger;
-    search<std::memory_order_acquire>(key[i], root, version[i], finger);
+  struct StepwiseFirstGeq {
 
-    if (finger.searchPathSize() > 0 && finger.backNode() == 0) {
-      move<std::memory_order_acquire, true>(finger, version[i]);
-      if (finger.searchPathSize() > 0) {
-        assert(finger.backNode() != 0);
+    const VersionedMap::Impl *map;
+    const weaselab::VersionedMap::Key *key;
+    const int64_t *version;
+    weaselab::VersionedMap::Iterator *iterator;
+    uint32_t node;
+
+    void begin(RootSet::ThreadSafeHandle handle) {
+      if (iterator->impl != nullptr) {
+        node = iterator->impl->version == *version
+                   ? iterator->impl->finger.root()
+                   : handle.rootForVersion(*version);
+        iterator->impl->~Impl();
+        new (iterator->impl) Iterator::Impl();
+      } else {
+        node = handle.rootForVersion(*version);
+        iterator->impl =
+            new (safe_malloc(sizeof(Iterator::Impl))) Iterator::Impl();
       }
     }
 
-    iterator[i].impl->version = version[i];
-    iterator[i].impl->map = this;
+    bool step() {
+      Finger &finger = iterator->impl->finger;
+      map->search<std::memory_order_acquire>(*key, node, *version, finger);
+      return true;
+    }
 
-    const Entry *prev = nullptr;
-    for (;;) {
-      if (finger.searchPathSize() == 0) {
-        break;
-      } else {
-        materializeMutations(iterator[i].impl, prev, nullptr);
-        for (int j = 0; j < iterator[i].impl->mutationCount; ++j) {
-          if (geq(iterator[i].impl->mutations[j], key[i])) {
-            iterator[i].impl->mutationIndex = j;
-            goto loopEnd;
-          }
+    void end() {
+      Finger &finger = iterator->impl->finger;
+      if (finger.searchPathSize() > 0 && finger.backNode() == 0) {
+        map->move<std::memory_order_acquire, true>(finger, *version);
+        if (finger.searchPathSize() > 0) {
+          assert(finger.backNode() != 0);
         }
       }
-      prev = iterator[i].impl->map->mm.base[finger.backNode()].entry;
-      iterator[i].impl->map->move<std::memory_order_acquire, true>(
-          finger, iterator[i].impl->version);
+
+      iterator->impl->version = *version;
+      iterator->impl->map = map;
+
+      const Entry *prev = nullptr;
+      for (;;) {
+        if (finger.searchPathSize() == 0) {
+          break;
+        } else {
+          materializeMutations(iterator->impl, prev, nullptr);
+          for (int j = 0; j < iterator->impl->mutationCount; ++j) {
+            if (geq(iterator->impl->mutations[j], *key)) {
+              iterator->impl->mutationIndex = j;
+              goto loopEnd;
+            }
+          }
+        }
+        prev = iterator->impl->map->mm.base[finger.backNode()].entry;
+        iterator->impl->map->move<std::memory_order_acquire, true>(
+            finger, iterator->impl->version);
+      }
+    loopEnd:;
     }
-  loopEnd:;
+  };
+
+  // Use stack allocation for small count
+  Arena arena;
+  constexpr int kStackAllocThreshold = 2;
+  StepwiseFirstGeq stepwiseStackAlloc[kStackAllocThreshold];
+  int nextJobStackAllocation[kStackAllocThreshold];
+  StepwiseFirstGeq *stepwise;
+  int *nextJob;
+  if (count <= kStackAllocThreshold) {
+    stepwise = stepwiseStackAlloc;
+    nextJob = nextJobStackAllocation;
+  } else {
+    stepwise = new (arena) StepwiseFirstGeq[count];
+    nextJob = new (arena) int[count];
+  }
+
+  auto handle = roots.getThreadSafeHandle();
+  for (int i = 0; i < count; ++i) {
+    stepwise[i].map = this;
+    stepwise[i].key = &key[i];
+    stepwise[i].version = &version[i];
+    stepwise[i].iterator = &iterator[i];
+    stepwise[i].begin(handle);
+    nextJob[i] = i + 1;
+  }
+  nextJob[count - 1] = 0;
+  int prevJob = count - 1;
+  int job = 0;
+
+  for (;;) {
+    if (stepwise[job].step()) {
+      stepwise[job].end();
+      if (job == prevJob) {
+        break;
+      }
+      nextJob[prevJob] = nextJob[job];
+      job = prevJob;
+    }
+    prevJob = job;
+    job = nextJob[job];
   }
 }