[llvm] ed9de61 - [SimplifyCFGPass] mergeEmptyReturnBlocks(): switch to non-permissive DomTree updates

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2021-01-05T01:26:36+03:00
New Revision: ed9de61cc3e280f84e3f0f98a49af21c7e59c4c9

URL: https://github.com/llvm/llvm-project/commit/ed9de61cc3e280f84e3f0f98a49af21c7e59c4c9
DIFF: https://github.com/llvm/llvm-project/commit/ed9de61cc3e280f84e3f0f98a49af21c7e59c4c9.diff

LOG: [SimplifyCFGPass] mergeEmptyReturnBlocks(): switch to non-permissive DomTree updates

... which requires not inserting an edge that already exists.

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 2c3454c46b30..c0edde8648f5 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -77,7 +77,6 @@ STATISTIC(NumSimpl, "Number of blocks simplified");
 
 /// If we have more than one empty (other than phi node) return blocks,
 /// merge them together to promote recursive block merging.
-// FIXME: switch to non-permissive DomTreeUpdater::applyUpdates().
 static bool mergeEmptyReturnBlocks(Function &F, DomTreeUpdater *DTU) {
   bool Changed = false;
 
@@ -143,7 +142,10 @@ static bool mergeEmptyReturnBlocks(Function &F, DomTreeUpdater *DTU) {
       if (DTU) {
         for (auto *Predecessor : predecessors(&BB)) {
           Updates.push_back({DominatorTree::Delete, Predecessor, &BB});
-          Updates.push_back({DominatorTree::Insert, Predecessor, RetBlock});
+          // But, iff Predecessor already branches to RetBlock,
+          // don't (re-)add DomTree edge, because it already exists.
+          if (!is_contained(successors(Predecessor), RetBlock))
+            Updates.push_back({DominatorTree::Insert, Predecessor, RetBlock});
         }
       }
       BB.replaceAllUsesWith(RetBlock);
@@ -176,7 +178,7 @@ static bool mergeEmptyReturnBlocks(Function &F, DomTreeUpdater *DTU) {
   }
 
   if (DTU) {
-    DTU->applyUpdatesPermissive(Updates);
+    DTU->applyUpdates(Updates);
     for (auto *BB : DeadBlocks)
       DTU->deleteBB(BB);
   } else {