[PATCH] D106645: [clangd] Tweak constructor of dex AndIterator for performance.

[Sam McCall via Phabricator via cfe-commits]

sammccall created this revision.
sammccall added a reviewer: kbobyrev.
Herald added subscribers: usaxena95, kadircet, arphaman.
sammccall requested review of this revision.
Herald added subscribers: cfe-commits, MaskRay, ilya-biryukov.
Herald added a project: clang-tools-extra.

Calling sync() *after* we sort the children is faster.
Also bail out early if some child is already at end.

This seems safe and should improve perf though only slightly


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106645

Files:
  clang-tools-extra/clangd/index/dex/Iterator.cpp


Index: clang-tools-extra/clangd/index/dex/Iterator.cpp
===================================================================
--- clang-tools-extra/clangd/index/dex/Iterator.cpp
+++ clang-tools-extra/clangd/index/dex/Iterator.cpp
@@ -27,10 +27,6 @@
   explicit AndIterator(std::vector<std::unique_ptr<Iterator>> AllChildren)
       : Iterator(Kind::And), Children(std::move(AllChildren)) {
     assert(!Children.empty() && "AND iterator should have at least one child.");
-    // Establish invariants.
-    for (const auto &Child : Children)
-      ReachedEnd |= Child->reachedEnd();
-    sync();
     // When children are sorted by the estimateSize(), sync() calls are more
     // effective. Each sync() starts with the first child and makes sure all
     // children point to the same element. If any child is "above" the previous
@@ -42,6 +38,10 @@
                             const std::unique_ptr<Iterator> &RHS) {
       return LHS->estimateSize() < RHS->estimateSize();
     });
+    // Establish invariants.
+    for (const auto &Child : Children)
+      ReachedEnd |= Child->reachedEnd();
+    sync();
   }
 
   bool reachedEnd() const override { return ReachedEnd; }


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