[TailCallElim] Preserve DT and PDT
Summary:
Previously, in the NewPM pipeline, TailCallElim recalculates the DomTree when it modifies any instruction in the Function.
For example,
```
CallInst *CI = dyn_cast<CallInst>(&I);
...
CI->setTailCall();
Modified = true;
...
if (!Modified || ...)
return PreservedAnalyses::all();
```
After applying this patch, the DomTree only recalculates if needed (plus an extra insertEdge() + an extra deleteEdge() call).
When optimizing SQLite with `-passes="default<O3>"` pipeline of the newPM, the number of DomTree recalculation decreases by 6.2%, the number of nodes visited by DFS decreases by 2.9%. The time used by DomTree will decrease approximately 1%~2.5% after applying the patch.
Statistics:
```
Before the patch:
23010 dom-tree-stats - Number of DomTree recalculations
489264 dom-tree-stats - Number of nodes visited by DFS -- DomTree
After the patch:
21581 dom-tree-stats - Number of DomTree recalculations
475088 dom-tree-stats - Number of nodes visited by DFS -- DomTree
```
Reviewers: kuhar, dmgreen, brzycki, grosser, davide
Reviewed By: kuhar, brzycki
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D49982
llvm-svn: 338954
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 7f61477..94f37da 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -646,7 +646,8 @@
}
ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
- BasicBlock *Pred) {
+ BasicBlock *Pred,
+ DomTreeUpdater *DTU) {
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
@@ -680,6 +681,10 @@
// longer branch to them.
BB->removePredecessor(Pred);
UncondBranch->eraseFromParent();
+
+ if (DTU)
+ DTU->deleteEdge(Pred, BB);
+
return cast<ReturnInst>(NewRet);
}