[llvm] [llvm][NFC] Assert VAArg type (PR #67148)

[Nathan Sidwell via llvm-commits]

https://github.com/urnathan created https://github.com/llvm/llvm-project/pull/67148

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 :)


>From f28424e11c58b564acebadb694d8a804435be437 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan at acm.org>
Date: Fri, 22 Sep 2023 10:22:57 -0400
Subject: [PATCH] [llvm][NFC] Assert VAArg type

Assert that VAArg is not given a structure or array type, for those
absolutely won't work (as documented in LangRef.rst).
---
 llvm/include/llvm/IR/Instructions.h | 4 ++++
 1 file changed, 4 insertions(+)

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);
   }