Recommit "[GlobalOpt] Pass DTU to removeUnreachableBlocks instead of recomputing."

The cause for the revert should be fixed by r373513 /
a80b6c15425f82521c624ff24c5c0a34cd534d54

This reverts commit 47dbcbd8ec6bf6c0b9cbe5811e81a37cc55e73ef.

llvm-svn: 373522

1 files changed, 3 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 9c7fd5e1a81..feac1b60884 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2285,14 +2285,10 @@ OptimizeFunctions(Module &M,
     // So, remove unreachable blocks from the function, because a) there's
     // no point in analyzing them and b) GlobalOpt should otherwise grow
     // some more complicated logic to break these cycles.
-    // Removing unreachable blocks might invalidate the dominator so we
-    // recalculate it.
     if (!F->isDeclaration()) {
-      if (removeUnreachableBlocks(*F)) {
-        auto &DT = LookupDomTree(*F);
-        DT.recalculate(*F);
-        Changed = true;
-      }
+      auto &DT = LookupDomTree(*F);
+      DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+      Changed |= removeUnreachableBlocks(*F, &DTU);
     }
 
     Changed |= processGlobal(*F, GetTLI, LookupDomTree);