[CallSiteSplitting] Do not perform callsite splitting inside landing pad

Summary:
If the callsite is inside landing pad, do not perform callsite splitting.

Callsite splitting uses utility function llvm::DuplicateInstructionsInSplitBetween, which eventually calls llvm::SplitEdge. llvm::SplitEdge calls llvm::SplitCriticalEdge with an assumption that the function returns nullptr only when the target edge is not a critical edge (and further assumes that if the return value was not nullptr, the predecessor of the original target edge always has a single successor because critical edge splitting was successful). However, this assumtion is not true because SplitCriticalEdge returns nullptr if the destination block is a landing pad. This invalid assumption results assertion failure.

Fundamental solution might be fixing llvm::SplitEdge to not to rely on the invalid assumption. However, it'll involve a lot of work because current API assumes that llvm::SplitEdge never fails. Instead, this patch makes callsite splitting to not to attempt splitting if the callsite is in a landing pad.

Attached test case will crash with assertion failure without the fix.

Reviewers: fhahn, junbuml, dberlin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45130

llvm-svn: 329250

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp b/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
index 796177b5f85..2a29c08a655 100644
--- a/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ b/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -206,6 +206,12 @@ static bool canSplitCallSite(CallSite CS, TargetTransformInfo &TTI) {
       isa<IndirectBrInst>(Preds[1]->getTerminator()))
     return false;
 
+  // Do not split a call-site in an exception handling block. This check
+  // prevents triggering an assertion in SplitEdge used via
+  // DuplicateInstructionsInSplitBetween. 
+  if (CallSiteBB->isEHPad())
+    return false;
+
   return CallSiteBB->canSplitPredecessors();
 }