[clang] [lldb] [clang][lldb] Don't assert structure layout correctness for layouts provided by LLDB (PR #93809)

[David Blaikie via cfe-commits]

dwblaikie wrote:

Here's the smallest patch that would put explicit alignment on any packed structure:
```
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index a072475ba770..bbb13ddd593b 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -64,7 +64,7 @@ static uint32_t getTypeAlignIfRequired(const Type *Ty, const ASTContext &Ctx) {
   // MaxFieldAlignmentAttr is the attribute added to types
   // declared after #pragma pack(n).
   if (auto *Decl = Ty->getAsRecordDecl())
-    if (Decl->hasAttr<MaxFieldAlignmentAttr>())
+    if (Decl->hasAttr<MaxFieldAlignmentAttr>() || Decl->hasAttr<PackedAttr>())
       return TI.Align;
 
   return 0;
```

But I don't think that's the right approach - I think what we should do is compute the natural alignment of the structure, then compare that to the actual alignment - and if they differ, we should put an explicit alignment on the structure. This avoids the risk that other alignment-influencing effects might be missed (and avoids the case of putting alignment on a structure that, when packed, just has the same alignment anyway - which is a minor issue, but nice to get right (eg: packed struct of a single char probably shouldn't have an explicit alignment - since it's the same as the implicit alignment anyway))



https://github.com/llvm/llvm-project/pull/93809