TargetExtType: guard against the case that there is no layout type

[nhaehnle]

Summary

This is hit by the verifier when looking at call arguments / return
type. There is a test in a subsequent commit.

[nikic]

Hm, is this supposed to be allowed? I thought we'd always have a layout type -- an unsized one if nothing else?

[nhaehnle]

There's nothing right now that would prevent this. Though we could default the layout type to something other than nullptr, if that is preferred. Maybe void?

[nikic]

In D150368#4346325, @nhaehnle wrote:

There's nothing right now that would prevent this. Though we could default the layout type to something other than nullptr, if that is preferred. Maybe void?

Isn't this already the default? https://github.com/llvm/llvm-project/blob/788e6ff4e5e6414c6707e91e95829f1d7c76b1aa/llvm/lib/IR/Type.cpp#L876

[nhaehnle]

Ah, my bad. I was working with local changes for so long that I hadn't noticed this got lost somehow. Sorry about that. I will follow-up with an adjustment to my later typeinfo diff.

llvm/lib/IR/Type.cpp

 
 bool Type::isSizedDerivedType(SmallPtrSetImpl<Type*> *Visited) const {
   if (auto *ATy = dyn_cast<ArrayType>(this))
     return ATy->getElementType()->isSized(Visited);
 
   if (auto *VTy = dyn_cast<VectorType>(this))
     return VTy->getElementType()->isSized(Visited);
 
-  if (auto *TTy = dyn_cast<TargetExtType>(this))
-    return TTy->getLayoutType()->isSized(Visited);
+  if (auto *TTy = dyn_cast<TargetExtType>(this)) {
+    if (Type *LTy = TTy->getLayoutType())
+      return LTy->isSized(Visited);
+    return false;
+  }
 
   return cast<StructType>(this)->isSized(Visited);
 }
 
 //===----------------------------------------------------------------------===//
 //                          Primitive 'Type' data
 //===----------------------------------------------------------------------===//