1 files changed, 65 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index e435537c3a7..ce550dc7fd1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2905,26 +2905,80 @@ bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
   // exception then zap the landing pad, turning its invokes into calls.
   BasicBlock *BB = RI->getParent();
   LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
-  if (RI->getValue() != LPInst)
-    // Not a landing pad, or the resume is not unwinding the exception that
-    // caused control to branch here.
+
+  // If RI->getValue() is a landing pad, check if the first instruction is
+  // the same landing pad that caused control to branch here. If RI->getValue
+  // is a phi of landing pad, check its predecessor blocks to see if any of
+  // them contains a trivial landing pad.
+  if (RI->getValue() != LPInst && !isa<PHINode>(RI->getValue()))
     return false;
 
-  // Check that there are no other instructions except for debug intrinsics.
-  BasicBlock::iterator I = LPInst->getIterator(), E = RI->getIterator();
+  // Check that there are no other instructions except for debug intrinsics
+  // between the landing pad (or phi of landing pad) and resume instruction.
+  BasicBlock::iterator I = cast<Instruction>(RI->getValue()), E = RI;
   while (++I != E)
     if (!isa<DbgInfoIntrinsic>(I))
       return false;
 
+  SmallVector<BasicBlock *, 4> TrivialUnwindBlocks;
+  if (RI->getValue() == LPInst) {
+    // Landing pad is in current block, which has already been checked.
+    TrivialUnwindBlocks.push_back(BB);
+  } else {
+    // Check incoming blocks to see if any of them are trivial.
+    auto *PhiLPInst = cast<PHINode>(RI->getValue());
+    for (unsigned i = 0; i < PhiLPInst->getNumIncomingValues(); i++) {
+      auto *IncomingBB = PhiLPInst->getIncomingBlock(i);
+      auto *IncomingValue = PhiLPInst->getIncomingValue(i);
+
+      auto *LandingPad =
+          dyn_cast<LandingPadInst>(IncomingBB->getFirstNonPHI());
+      // Not the landing pad that caused the control to branch here.
+      if (IncomingValue != LandingPad)
+        continue;
+
+      bool isTrivial = true;
+
+      I = IncomingBB->getFirstNonPHI();
+      E = IncomingBB->getTerminator();
+      while (++I != E)
+        if (!isa<DbgInfoIntrinsic>(I)) {
+          isTrivial = false;
+          break;
+        }
+
+      if (isTrivial)
+        TrivialUnwindBlocks.push_back(IncomingBB);
+    }
+  }
+
   // Turn all invokes that unwind here into calls and delete the basic block.
-  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
-    BasicBlock *Pred = *PI++;
-    removeUnwindEdge(Pred);
+  for (auto *TrivialBB : TrivialUnwindBlocks) {
+    if (isa<PHINode>(RI->getValue())) {
+      // Blocks that will be deleted should also be removed
+      // from the phi node.
+      BB->removePredecessor(TrivialBB, true);
+    }
+
+    for (pred_iterator PI = pred_begin(TrivialBB), PE = pred_end(TrivialBB);
+         PI != PE;) {
+      BasicBlock *Pred = *PI++;
+      removeUnwindEdge(Pred);
+    }
+
+    // The landingpad is now unreachable.  Zap it.
+    if (TrivialBB == BB)
+      BB = nullptr;
+    TrivialBB->eraseFromParent();
   }
 
-  // The landingpad is now unreachable.  Zap it.
-  BB->eraseFromParent();
-  return true;
+  // Delete the resume block if all its predecessors have been deleted, and we
+  // haven't already deleted it above when deleting the landing pad blocks.
+  if (BB && pred_begin(BB) == pred_end(BB)) {
+    BB->eraseFromParent();
+  }
+
+  return TrivialUnwindBlocks.size() != 0;
 }
 
 bool SimplifyCFGOpt::SimplifyCleanupReturn(CleanupReturnInst *RI) {