Re: [eigen] Proposal to remove aligned alloc paths

Overriding Malloc on Mac OS X systems is an especially bad idea. Apple has spent a lot of engineering time and effort working with internal teams to integrate the Malloc implementation deeply into the many various frameworks, and then building performance tools that rely on features of the system Malloc.

I acknowledge that Eigen is not just a typical code library, and on some platforms the libc Malloc might not accommodate vector alignment requirements. But Mac OS X is not one of those platforms, and thus a library that blindly overrides Malloc is causing wholly unnecessary breakage of numerous system features.

I have admittedly not reviewed either Eigen's existing code paths or the proposed changes, but I wanted to offer a different perspective on the trade-offs inherent in substituting Malloc implementations on different platforms.

Sent from my iPad

On Dec 13, 2014, at 4:25 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:

Motivation for these changes, aside from removing code:

The "malloc is already aligned" path relies on the assumption that malloc's nonstandard properties are only a function of the platform, which we tried to detect using preprocessor tokens. But malloc is not a system feature, it's a C library feature and many applications override it. Thus, we can't know if malloc is already aligned based on platform checks.