[llvm][NFC] Assert VAArg type

[urnathan]

Due to the way we have a backend arranged, we fell over a varadic struct bug, and noticed the generic machinery presumes all by-val structs are by hidden pointer. The documentation even warns:

'Note that the code generator does not yet fully support va_arg on many targets. Also, it does not currently support va_arg with aggregate types on any target.'

While this assert would not have triggered in our case, it was surprising to not see a check. So here's one. Of course it doesn't trigger :)

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Changes

Due to the way we have a backend arranged, we fell over a varadic struct bug, and noticed the generic machinery presumes all by-val structs are by hidden pointer. The documentation even warns:

'Note that the code generator does not yet fully support va_arg on many targets. Also, it does not currently support va_arg with aggregate types on any target.'

While this assert would not have triggered in our case, it was surprising to not see a check. So here's one. Of course it doesn't trigger :)

---

Full diff: https://github.com/llvm/llvm-project/pull/67148.diff

1 Files Affected:

• (modified) llvm/include/llvm/IR/Instructions.h (+4)

diff --git a/llvm/include/llvm/IR/Instructions.h b/llvm/include/llvm/IR/Instructions.h
index a0c8406fe4ec1e5..cfe90ecdef3fd5a 100644
--- a/llvm/include/llvm/IR/Instructions.h
+++ b/llvm/include/llvm/IR/Instructions.h
@@ -1796,12 +1796,16 @@ class VAArgInst : public UnaryInstruction {
   VAArgInst(Value *List, Type *Ty, const Twine &NameStr = "",
              Instruction *InsertBefore = nullptr)
     : UnaryInstruction(Ty, VAArg, List, InsertBefore) {
+    assert(!Ty->isStructTy() && !Ty->isArrayTy() &&
+           "by-val structures and arrays unsupported");
     setName(NameStr);
   }
 
   VAArgInst(Value *List, Type *Ty, const Twine &NameStr,
             BasicBlock *InsertAtEnd)
     : UnaryInstruction(Ty, VAArg, List, InsertAtEnd) {
+    assert(!Ty->isStructTy() && !Ty->isArrayTy() &&
+           "by-val structures and arrays unsupported");
     setName(NameStr);
   }