[PATCH] D62981: [DomTreeUpdater] Add all insert before all delete updates to reduce compile time.

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea created this revision.
asbirlea added reviewers: kuhar, NutshellySima, mstorsjo.
Herald added a subscriber: jlebar.
Herald added a project: LLVM.

The cleanup in D62751 <https://reviews.llvm.org/D62751> introduced a compile-time regression due to the way DT updates are performed.
Add all insert edges then all delete edges in DTU to match the previous compile time.
Compile time on the test provided by @mstorsjo before and after this patch on my machine:
113.046s vs 35.649s
Repro: clang -target x86_64-w64-mingw32 -c -O3 glew-preproc.c; on https://martin.st/temp/glew-preproc.c.


Repository:
  rL LLVM

https://reviews.llvm.org/D62981

Files:
  lib/Transforms/Utils/BasicBlockUtils.cpp


Index: lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- lib/Transforms/Utils/BasicBlockUtils.cpp
+++ lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -212,13 +212,14 @@
   std::vector<DominatorTree::UpdateType> Updates;
   if (DTU) {
     Updates.reserve(1 + (2 * succ_size(BB)));
-    Updates.push_back({DominatorTree::Delete, PredBB, BB});
-    for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
-      Updates.push_back({DominatorTree::Delete, BB, *I});
+    // Add insert edges first.
+    for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
       // This successor of BB may already have PredBB as a predecessor.
       if (llvm::find(successors(PredBB), *I) == succ_end(PredBB))
         Updates.push_back({DominatorTree::Insert, PredBB, *I});
-    }
+    for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
+      Updates.push_back({DominatorTree::Delete, BB, *I});
+    Updates.push_back({DominatorTree::Delete, PredBB, BB});
   }
 
   if (MSSAU)


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