[SplitLandingPadPredecessors] Create a PHINode for the original landingpad only if it has some uses

Summary: This patch adds a check in SplitLandingPadPredecessors to see if the original landingpad instruction has any uses. If not, we don't need to create a PHINode for it in the joint block since it's gonna be a dead code anyway. The motivation for this patch is that we found a bug that SplitLandingPadPredecessors created a PHINode of token type landingpad, which failed the verifier since PHINode can not be token type. However, the created PHINode will never be used in our code pattern. This patch will workaround this bug, and we might add supports in SplitLandingPadPredecessors to handle token type landingpad with uses in the future.

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15835

llvm-svn: 256972

1 files changed, 11 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index a5137e933e8..72db980cf57 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -626,11 +626,17 @@ void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
     Clone2->setName(Twine("lpad") + Suffix2);
     NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
 
-    // Create a PHI node for the two cloned landingpad instructions.
-    PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
-    PN->addIncoming(Clone1, NewBB1);
-    PN->addIncoming(Clone2, NewBB2);
-    LPad->replaceAllUsesWith(PN);
+    // Create a PHI node for the two cloned landingpad instructions only
+    // if the original landingpad instruction has some uses.
+    if (!LPad->use_empty()) {
+      assert(!LPad->getType()->isTokenTy() &&
+             "Split cannot be applied if LPad is token type. Otherwise an "
+             "invalid PHINode of token type would be created.");
+      PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
+      PN->addIncoming(Clone1, NewBB1);
+      PN->addIncoming(Clone2, NewBB2);
+      LPad->replaceAllUsesWith(PN);
+    }
     LPad->eraseFromParent();
   } else {
     // There is no second clone. Just replace the landing pad with the first