[JumpThreading] PR36133 enable/disable DominatorTree for LVI analysis

Summary:
The LazyValueInfo pass caches a copy of the DominatorTree when available.
Whenever there are pending DominatorTree updates within JumpThreading's
DeferredDominance object we cannot use the cached DT for LVI analysis.
This commit adds the new methods enableDT() and disableDT() to LVI.
JumpThreading also sets the appropriate usage model before calling LVI
analysis methods.

Fixes https://bugs.llvm.org/show_bug.cgi?id=36133

Reviewers: sebpop, dberlin, kuhar

Reviewed by: sebpop, kuhar

Subscribers: uabelho, llvm-commits, aprantl, hiraditya, a.elovikov

Differential Revision: https://reviews.llvm.org/D42717

llvm-svn: 325356

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/IR/Dominators.cpp b/llvm/lib/IR/Dominators.cpp
index 25e4ce4e4ef..1429e1b9060 100644
--- a/llvm/lib/IR/Dominators.cpp
+++ b/llvm/lib/IR/Dominators.cpp
@@ -448,6 +448,9 @@ bool DeferredDominance::pendingDeletedBB(BasicBlock *DelBB) {
   return DeletedBBs.count(DelBB) != 0;
 }
 
+/// \brief Returns true if pending DT updates are queued for a flush() event.
+bool DeferredDominance::pending() { return !PendUpdates.empty(); }
+
 /// \brief Flushes all pending updates and block deletions. Returns a
 /// correct DominatorTree reference to be used by the caller for analysis.
 DominatorTree &DeferredDominance::flush() {