[PATCH] D118804: Revert "[Clang] Propagate guaranteed alignment for malloc and others"

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D118804#3291060 <https://reviews.llvm.org/D118804#3291060>, @xbolva00 wrote:

> Or can we bailout just for gnu? and preserve this for darwin?

As is, the original patch applies the C++ getNewAlign to C calloc/malloc/strdup/etc. This is outright wrong.

For C++, I confess I have some problems interpreting this sentence:

(https://eel.is/c++draft/cpp.predefined)

> `__STDCPP_­DEFAULT_­NEW_­ALIGNMENT__`:  An integer literal of type std::size_t whose value is the alignment guaranteed by a call to operator new(std::size_t) or operator new[](std::size_t). [ Note: Larger alignments will be passed to operator new(std::size_t, std::align_val_t), etc. (8.3.4). — end note ]

It seems to suggest that a large alignment may be assumed, but practically, I know at least mimalloc uses 8-byte alignment for 64-bit Darwin, not 16-byte alignment.

> Or can we bailout just for gnu? and preserve this for darwin?

If deemed useful, someone may create a subsequent patch applying a fixed/restricted form.
This needs to be very careful since `__STDCPP_­DEFAULT_­NEW_­ALIGNMENT__` doesn't seem to match the practice.


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https://reviews.llvm.org/D118804