rsmith added inline comments.
================
Comment at: lib/CodeGen/CGDebugInfo.cpp:2812-2814
+ // Implicitly by reference is everything clearly looks like a non-pod type:
+ // - Types that define a destructor, a copy constructor, and a copy
+ // assignment operator.
----------------
I do not believe this is sufficient. Consider:
```
struct A {
A(const A&) = default;
A(A&);
};
struct B : A {};
```
Now, `A` is passed indirectly, because it has a non-trivial copy constructor
(`A::A(A&)`). But `B` is passed directly, because it only has a trivial copy
constructor, despite having an `A` subobject.
I would not expect debuggers to get intricacies like this right. (In general,
determining how to pass a class like `B` can require performing template
instantiation, which it's clearly not reasonable to expect a debugger to do.)
If you want to give the debugger a hint for any type that's non-POD (as the
comment says), then use `CXXRecordDecl::isPOD` to determine that. I think it is
reasonable to believe that a debugger will figure out that objects of POD types
are passed direct.
================
Comment at: lib/CodeGen/CGDebugInfo.cpp:2817
+ if (auto CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
+ if (CXXRD->isTriviallyCopyable()) {
+ if (CXXRD->hasUserDeclaredDestructor() ||
----------------
"isTriviallyCopyable()" is the wrong thing to check here. The best you can do
to get a per-type "calling convention" value is to call
`CGCXXABI::getRecordArgABI`.
However, that does not tell the full story: in particular, in the MS ABI,
member functions always return objects of class type indirectly, regardless of
whether they could otherwise be returned in registers. If DWARF 5 allows you to
override the calling convention on a particular usage of a type, you can check
whether a function's return type should be indirect by calling
`CGCXXABI::classifyReturnType`.
================
Comment at: lib/CodeGen/CGDebugInfo.cpp:2821-2822
+ CXXRD->hasUserDeclaredMoveConstructor() ||
+ CXXRD->hasUserDeclaredCopyAssignment() ||
+ CXXRD->hasUserDeclaredMoveAssignment())
+ Flags |= llvm::DINode::FlagTypePassByValue;
----------------
The assignment operators are irrelevant here. Does any debugger really base its
calling convention decision on their existence?
================
Comment at: lib/CodeGen/CGDebugInfo.cpp:2825-2827
+ if (!CXXRD->hasUserDeclaredDestructor() &&
+ !CXXRD->hasUserDeclaredCopyConstructor() &&
+ !CXXRD->hasUserDeclaredCopyAssignment())
----------------
Why are you not checking for move operations on this side?
Repository:
rL LLVM
https://reviews.llvm.org/D41743
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