ConstantFolding: Guard use of getFunction

[dstuttard]

Summary

Add additional guards for a use of getFunction on an Instruction
In some cases constanfFoldCanonicalize can be called with a cloned instruction
that doesn't have a parent (or associated function), causing a seg fault.

[dstuttard]

Managed to get arc diff to work!

[arsenm]

Seems a bit broken that this is reachable. Unit test would be nice

[arsenm]

Actually, this shows there's a bug here. getFunction shouldn't be relevant The call below should be looking at the parent function

[arsenm]

getFunction is not getCalledFunction

llvm/lib/Analysis/ConstantFolding.cpp

static Constant *constantFoldCanonicalize(const Type *Ty, const CallBase *CI,
 
   // Zero is always canonical and the sign must be preserved.
   //
   // Denorms and nans may have special encodings, but it should be OK to fold a
   // totally average number.
   if (Src.isNormal() || Src.isInfinity())
     return ConstantFP::get(CI->getContext(), Src);
 
-  if (Src.isDenormal()) {
+  if (Src.isDenormal() && CI->getParent() && CI->getFunction()) {
     DenormalMode DenormMode =
         CI->getFunction()->getDenormalMode(Src.getSemantics());
     if (DenormMode == DenormalMode::getIEEE())
       return nullptr;
 
     bool IsPositive = !Src.isNegative() ||
                       DenormMode.Input == DenormalMode::PositiveZero ||
                       DenormMode.Output == DenormalMode::PositiveZero;