Revert "[SimplifyCFG] Check if the return instruction causes undefined behavior"

Breaks bots
https://lab.llvm.org/buildbot/#/builders/236/builds/2349
https://lab.llvm.org/buildbot/#/builders/74/builds/17361
https://lab.llvm.org/buildbot/#/builders/168/builds/11972

This reverts commit 7be55b007698f6b6398cbbea69c327b5a971938a.

1 files changed, 0 insertions, 14 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index f6d3022..372a669 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7126,20 +7126,6 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
         return passingValueIsAlwaysUndefined(V, GEP, PtrValueMayBeModified);
       }
 
-    // Look through return.
-    if (ReturnInst *Ret = dyn_cast<ReturnInst>(Use)) {
-      bool HasNoUndefAttr =
-          Ret->getFunction()->hasRetAttribute(Attribute::NoUndef);
-      // Return undefined to a noundef return value is undefined.
-      if (isa<UndefValue>(C) && HasNoUndefAttr)
-        return true;
-      // Return null to a nonnull+noundef return value is undefined.
-      if (C->isNullValue() && HasNoUndefAttr &&
-          Ret->getFunction()->hasRetAttribute(Attribute::NonNull)) {
-        return true;
-      }
-    }
-
     // Look through bitcasts.
     if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
       return passingValueIsAlwaysUndefined(V, BC, PtrValueMayBeModified);