[llvm] 13fca9d - [NFCI][SimplifyCFG] mergeEmptyReturnBlocks(): improve Dominator Tree updating

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2021-04-11T23:56:23+03:00
New Revision: 13fca9d8161e3a203dce6d7647763a07d39bed3f

URL: https://github.com/llvm/llvm-project/commit/13fca9d8161e3a203dce6d7647763a07d39bed3f
DIFF: https://github.com/llvm/llvm-project/commit/13fca9d8161e3a203dce6d7647763a07d39bed3f.diff

LOG: [NFCI][SimplifyCFG] mergeEmptyReturnBlocks(): improve Dominator Tree updating

Same as with previous patches.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 38e7109ead57..f0702e00e380 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -142,13 +142,17 @@ static bool mergeEmptyReturnBlocks(Function &F, DomTreeUpdater *DTU) {
           cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0)) {
       // All predecessors of BB should now branch to RetBlock instead.
       if (DTU) {
-        for (auto *Predecessor : predecessors(&BB)) {
+        SmallPtrSet<BasicBlock *, 2> PredsOfBB(pred_begin(&BB), pred_end(&BB));
+        SmallPtrSet<BasicBlock *, 2> PredsOfRetBlock(pred_begin(RetBlock),
+                                                     pred_end(RetBlock));
+        Updates.reserve(Updates.size() + 2 * PredsOfBB.size());
+        for (auto *Predecessor : PredsOfBB)
           // But, iff Predecessor already branches to RetBlock,
           // don't (re-)add DomTree edge, because it already exists.
-          if (!is_contained(successors(Predecessor), RetBlock))
+          if (!PredsOfRetBlock.contains(Predecessor))
             Updates.push_back({DominatorTree::Insert, Predecessor, RetBlock});
+        for (auto *Predecessor : PredsOfBB)
           Updates.push_back({DominatorTree::Delete, Predecessor, &BB});
-        }
       }
       BB.replaceAllUsesWith(RetBlock);
       DeadBlocks.emplace_back(&BB);