[SimplifyCFG] Stop inserting calls to llvm.trap for UB

SimplifyCFG had logic to insert calls to llvm.trap for two very
particular IR patterns: stores and invokes of undef/null.

While InstCombine canonicalizes certain undefined behavior IR patterns
to stores of undef, phase ordering means that this cannot be relied upon
in general.

There are much better tools than llvm.trap: UBSan and ASan.

N.B. I could be argued into reverting this change if a clear argument as
to why it is important that we synthesize llvm.trap for stores, I'd be
hard pressed to see why it'd be useful for invokes...

llvm-svn: 273778

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 91e625b7aac..264bdb6f353 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -1802,8 +1802,7 @@ static bool runIPSCCP(Module &M, const DataLayout &DL,
         DEBUG(dbgs() << "  BasicBlock Dead:" << *BB);
 
         ++NumDeadBlocks;
-        NumInstRemoved +=
-            changeToUnreachable(BB->getFirstNonPHI(), /*UseLLVMTrap=*/false);
+        NumInstRemoved += changeToUnreachable(BB->getFirstNonPHI());
 
         MadeChanges = true;