jrtc27 wrote:
> > > > #112806 should address this without narrowing the field to 32 bits.
> > >
> > >
> > > As does [#111995
> > > (comment)](https://github.com/llvm/llvm-project/pull/111995#discussion_r1805329590),
> > > with less code and more generality
> >
> >
> > I prefer this solution too.
>
> That solution still violates the rules of the C++ object model.
How about:
```diff
diff --git a/clang/include/clang/AST/ExternalASTSource.h
b/clang/include/clang/AST/ExternalASTSource.h
index 385c32edbae0..766ebec2daf0 100644
--- a/clang/include/clang/AST/ExternalASTSource.h
+++ b/clang/include/clang/AST/ExternalASTSource.h
@@ -25,6 +25,7 @@
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
+#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
@@ -326,29 +327,46 @@ struct LazyOffsetPtr {
///
/// If the low bit is clear, a pointer to the AST node. If the low
/// bit is set, the upper 63 bits are the offset.
- mutable uint64_t Ptr = 0;
+ static constexpr size_t DataSize = std::max(sizeof(uint64_t), sizeof(T *));
+ alignas(uint64_t) alignas(T *) mutable unsigned char Data[DataSize] = {};
+
+ template <typename U> U &As(bool New) const {
+ unsigned char *Obj =
+ Data + (llvm::sys::IsBigEndianHost ? DataSize - sizeof(U) : 0);
+ if (New)
+ return *new (Obj) U;
+ return *std::launder(reinterpret_cast<U *>(Obj));
+ }
+
+ unsigned char &GetLSB() const { return As<unsigned char>(false); }
+ T *&GetPtr() const { return As<T *>(false); }
+ uint64_t &GetU64() const { return As<uint64_t>(false); }
+ void SetPtr(T *Ptr) const { As<T *>(true) = Ptr; }
+ void SetU64(uint64_t U64) const { As<uint64_t>(true) = U64; }
public:
LazyOffsetPtr() = default;
- explicit LazyOffsetPtr(T *Ptr) : Ptr(reinterpret_cast<uint64_t>(Ptr)) {}
+ explicit LazyOffsetPtr(T *Ptr) : Data() { SetPtr(Ptr); }
- explicit LazyOffsetPtr(uint64_t Offset) : Ptr((Offset << 1) | 0x01) {
+ explicit LazyOffsetPtr(uint64_t Offset) : Data() {
assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
if (Offset == 0)
- Ptr = 0;
+ SetPtr(NULL);
+ else
+ SetU64((Offset << 1) | 0x01);
}
LazyOffsetPtr &operator=(T *Ptr) {
- this->Ptr = reinterpret_cast<uint64_t>(Ptr);
+ SetPtr(Ptr);
return *this;
}
LazyOffsetPtr &operator=(uint64_t Offset) {
assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
if (Offset == 0)
- Ptr = 0;
+ SetPtr(NULL);
else
- Ptr = (Offset << 1) | 0x01;
+ SetU64((Offset << 1) | 0x01);
return *this;
}
@@ -356,15 +374,15 @@ public:
/// Whether this pointer is non-NULL.
///
/// This operation does not require the AST node to be deserialized.
- explicit operator bool() const { return Ptr != 0; }
+ explicit operator bool() const { return isOffset() || GetPtr() != NULL; }
/// Whether this pointer is non-NULL.
///
/// This operation does not require the AST node to be deserialized.
- bool isValid() const { return Ptr != 0; }
+ bool isValid() const { return isOffset() || GetPtr() != NULL; }
/// Whether this pointer is currently stored as an offset.
- bool isOffset() const { return Ptr & 0x01; }
+ bool isOffset() const { return GetLSB() & 0x01; }
/// Retrieve the pointer to the AST node that this lazy pointer points to.
///
@@ -375,9 +393,9 @@ public:
if (isOffset()) {
assert(Source &&
"Cannot deserialize a lazy pointer without an AST source");
- Ptr = reinterpret_cast<uint64_t>((Source->*Get)(OffsT(Ptr >> 1)));
+ SetPtr((Source->*Get)(OffsT(GetU64() >> 1)));
}
- return reinterpret_cast<T*>(Ptr);
+ return GetPtr();
}
/// Retrieve the address of the AST node pointer. Deserializes the pointee if
@@ -385,7 +403,7 @@ public:
T **getAddressOfPointer(ExternalASTSource *Source) const {
// Ensure the integer is in pointer form.
(void)get(Source);
- return reinterpret_cast<T**>(&Ptr);
+ return &GetPtr();
}
};
```
The std::launder may be unnecessary, I don't understand all the scenarios it's
needed.
https://github.com/llvm/llvm-project/pull/111995
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
