[SimpleLoopUnswitch] After unswitch delete dead blocks in parent loops

Summary:
Assert from PR38737 happens on the dead block inside the parent loop
after unswitching nontrivial switch in the inner loop.

deleteDeadBlocksFromLoop now takes extra care to detect/remove dead
blocks in all the parent loops in addition to the blocks from original
loop being unswitched.

Reviewers: asbirlea, chandlerc

Reviewed By: asbirlea

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D51415

llvm-svn: 340955

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 8b67c470a35..3cc2c651f6c 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -1380,13 +1380,21 @@ deleteDeadBlocksFromLoop(Loop &L,
                          DominatorTree &DT, LoopInfo &LI) {
   // Find all the dead blocks, and remove them from their successors.
   SmallVector<BasicBlock *, 16> DeadBlocks;
-  for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks))
+  for (BasicBlock *BB : ExitBlocks)
     if (!DT.isReachableFromEntry(BB)) {
       for (BasicBlock *SuccBB : successors(BB))
         SuccBB->removePredecessor(BB);
       DeadBlocks.push_back(BB);
     }
 
+  for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop())
+    for (BasicBlock *BB : ParentL->blocks())
+      if (!DT.isReachableFromEntry(BB)) {
+        for (BasicBlock *SuccBB : successors(BB))
+          SuccBB->removePredecessor(BB);
+        DeadBlocks.push_back(BB);
+      }
+
   SmallPtrSet<BasicBlock *, 16> DeadBlockSet(DeadBlocks.begin(),
                                              DeadBlocks.end());
 
@@ -1431,7 +1439,7 @@ deleteDeadBlocksFromLoop(Loop &L,
 
   // Actually delete the blocks now that they've been fully unhooked from the
   // IR.
-  for (auto *BB : DeadBlocks)
+  for (auto *BB : DeadBlockSet)
     BB->eraseFromParent();
 }