[Dominators] Don't compute DFS InOut numbers eagerly.

Summary:
DFS InOut numbers currently get eagerly computer upon DomTree construction. They are only needed to answer dome dominance queries and they get invalidated by updates and recalculations. Because of that, it is faster in practice to compute them lazily when they are actually needed.

Clang built without this patch takes 6m 45s to boostrap on my machine, and with the patch applied 6m 38s.

Reviewers: sanjoy, dberlin, chandlerc

Reviewed By: dberlin

Subscribers: davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D34296

llvm-svn: 306778

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/unittests/IR/DominatorTreeTest.cpp b/llvm/unittests/IR/DominatorTreeTest.cpp
index 232f0cbd4ed..5d3ef30177a 100644
--- a/llvm/unittests/IR/DominatorTreeTest.cpp
+++ b/llvm/unittests/IR/DominatorTreeTest.cpp
@@ -220,6 +220,7 @@ TEST(DominatorTree, Unreachable) {
         EXPECT_EQ(PostDominatedBBs.size(), 0UL);
 
         // Check DFS Numbers before
+        DT->updateDFSNumbers();
         EXPECT_EQ(DT->getNode(BB0)->getDFSNumIn(), 0UL);
         EXPECT_EQ(DT->getNode(BB0)->getDFSNumOut(), 7UL);
         EXPECT_EQ(DT->getNode(BB1)->getDFSNumIn(), 1UL);
@@ -235,6 +236,7 @@ TEST(DominatorTree, Unreachable) {
         DT->recalculate(F);
 
         // Check DFS Numbers after
+        DT->updateDFSNumbers();
         EXPECT_EQ(DT->getNode(BB0)->getDFSNumIn(), 0UL);
         EXPECT_EQ(DT->getNode(BB0)->getDFSNumOut(), 9UL);
         EXPECT_EQ(DT->getNode(BB1)->getDFSNumIn(), 1UL);