guiand marked an inline comment as done.
guiand added inline comments.
================
Comment at: clang/lib/CodeGen/CGCall.cpp:2082
+ const Type *RetTyPtr = RetTy.getTypePtr();
+ if (!RetTy->isVoidType() && !RetTyPtr->isRecordType() &&
+ RetAI.getKind() != ABIArgInfo::Indirect) {
----------------
rsmith wrote:
> Other types that we should think about from a padding perspective:
>
> * `nullptr_t` (which has the same size and alignment as `void*` but is all
> padding)
> * 80-bit `long double` and `_Complex long double` (I don't know whether we
> guarantee to initialize the 6 padding bytes)
> * member pointers might contain padding under some ABI rules -- under the MS
> ABI, you get a struct containing N pointers followed by M ints, which could
> have 4 bytes of tail padding on 64-bit targets
> * vector types with tail padding (eg, a vector of 3 `char`s is sometimes
> passed as an `i32` with one byte `undef`)
> * matrix types (presumably the same concerns as for vector types apply here)
> * maybe Obj-C object types?
> * `_ExtInt` types (eg, returning an `_ExtInt(65)` initialized to 0 produces
> an `{i64, i64}` containing 7 bytes of `undef`)
>
> It would be safer to list exactly those types for which we know this
> assumption is correct rather than assuming that it's correct by default -- I
> think more than half of the `Type` subclasses for concrete canonical types
> can have undef bits in their IR representation.
This is a good point, and I think there was some nuance that I had previously
included in determining this for records (since removed) that I didn't think to
include in CGCall.cpp.
I think one particular check, `llvm::DataLayout::typeSizeEqualsStoreSize`,
handles a lot of these cases:
- `long double`
- oddly-sized vectors
- `_ExtInt` types
I don't know if the `matrix` type has internal padding (like structs) but if
not it would cover that as well.
I believe that the struct with padding wouldn't be an issue as we're excluding
record types here.
And I'd have to take a closer look at `nullptr_t` to see how it behaves here.
~~~
But if I'd like to build an exhaustive list of types I think will work
correctly with a check like this:
- scalars
- floating point numbers
- pointers
I think I'd need also need an inner `typeSizeEqualsStoreSize` check on the base
type of vectors/complex numbers.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D81678/new/
https://reviews.llvm.org/D81678
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
