[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, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 2509b0a058f..a2dd581f45c 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -491,7 +491,7 @@ ReprocessLoop:
 
       // Zap the dead pred's terminator and replace it with unreachable.
       TerminatorInst *TI = P->getTerminator();
-      changeToUnreachable(TI, /*UseLLVMTrap=*/false);
+      changeToUnreachable(TI);
       Changed = true;
     }
   }