[PATCH] D70030: [MachineBlockPlacement] Update UnscheduledPredecessors when tail duplicate delete a block.

[Huihui Zhang via Phabricator via llvm-commits]

huihuiz updated this revision to Diff 229401.
huihuiz edited the summary of this revision.
huihuiz added a comment.

Addressed reviewer feedback -- add more explanation in comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70030/new/

https://reviews.llvm.org/D70030

Files:
  llvm/lib/CodeGen/MachineBlockPlacement.cpp


Index: llvm/lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -2949,9 +2949,33 @@
 
   SmallVector<MachineBasicBlock *, 8> DuplicatedPreds;
   bool IsSimple = TailDup.isSimpleBB(BB);
+  BlockChain &BBChain = *BlockToChain[BB];
   TailDup.tailDuplicateAndUpdate(IsSimple, BB, LPred,
                                  &DuplicatedPreds, &RemovalCallbackRef);
 
+  // Decrease UnscheduledPredecessors previously set for duplicated BB's
+  // BlockChain. Consider duplicate a BB from a chain(as BBChain in the CFG
+  // below) with multiple BBs, and PredBB is coming from different block
+  // chain(as PredChain). The UnscheduledPredecessors counter for BBChain was
+  // increased while calling fillWorkList for BB. When the duplicated BB becomes
+  // a dead block due to tail-duplication, build PredChain may not release the
+  // UnscheduledPredecessors counter for BBChain, as Succ1(also in BBChain) may
+  // not be in the BlockFilter previously collected for PredChain.
+  //
+  // PredBB [PredChain]        PredBB [PredChain]
+  //     \                             /  \
+  //      BB [BBChain]       =>   Succ0  Succ1 [BBChain]
+  //     /   \
+  //  Succ0 Succ1 [BBChain]
+  if (Removed)
+    for (MachineBasicBlock *Pred : DuplicatedPreds) {
+      if (BlockFilter && !BlockFilter->count(Pred))
+        continue;
+      if (&BBChain != BlockToChain[Pred] &&
+          BBChain.UnscheduledPredecessors != 0)
+        --BBChain.UnscheduledPredecessors;
+    }
+
   // Update UnscheduledPredecessors to reflect tail-duplication.
   DuplicatedToLPred = false;
   for (MachineBasicBlock *Pred : DuplicatedPreds) {


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