tree fee564f75e001520c59366ced0c966952756a920
parent 9c6fe66c587f0d880ed39852aef04fd2fa5e0f8c
author Fangrui Song <maskray@google.com> 1550637582 +0000
committer Fangrui Song <maskray@google.com> 1550637582 +0000

[Dominators] Simplify and optimize path compression used in link-eval forest.

Summary:
* NodeToInfo[*] have been allocated so the addresses are stable. We can store them instead of NodePtr to save NumToNode lookups.
* Nodes are traversed twice. Using `Visited` to check the traversal number is expensive and obscure. Just split the two traversals into two loops explicitly.
* The check `VInInfo.DFSNum < LastLinked` is redundant as it is implied by `VInInfo->Parent < LastLinked`
* VLabelInfo PLabelInfo are used to save a NodeToInfo lookup in the second traversal.

Also add some comments explaining eval().

This shows a ~4.5% improvement (9.8444s -> 9.3996s) on

    perf stat -r 10 taskset -c 0 opt -passes=$(printf '%.0srequire<domtree>,invalidate<domtree>,' {1..1000})'require<domtree>' -disable-output sqlite-autoconf-3270100/sqlite3.bc

Reviewers: kuhar, sanjoy, asbirlea

Reviewed By: kuhar

Subscribers: brzycki, NutshellySima, kristina, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58327

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354433 91177308-0d34-0410-b5e6-96231b3b80d8