On Fri, 2024-04-19 at 14:38 -0400, Dmitry Goncharov wrote: > On Fri, Apr 19, 2024 at 1:42 PM Paul Smith <psm...@gnu.org> wrote: > > The main advantages to alloca are twofold: > > > > 1) efficiency for small local buffers, which GNU Make uses a lot. > > > > 2) simplification of the code because you don't have to track this > > memory and ensure it's freed regardless of how the function > > returns. > > Dennis, do you see an alternative that is at least equally efficient, > simple and portable? One alternative that is equally efficient and > simple is variable length arrays. However, there is a question about > portability of vla vs alloca.
VLAs are strictly less powerful than alloca because alloca() is scoped to the function, while VLAs are scoped to the enclosing block. That is a serious flaw in VLAs and means that it is impossible for them to replace alloca() in many simple, obvious situations. In addition, while alloca() is best implemented by the compiler it IS possible to provide a standards-conforming implementation of them (which is less performant than a compiler-provided alloca(), but which works) which means that alloca() is more portable than VLAs, which will cause compiler errors in any compiler that doesn't support them. So, I have zero interest in VLAs. In my opinion they were a mistake from the first and should never have been implemented or standardized. I did share this opinion and provided examples of how limiting and limited they were back when they were being considered for standardization but, well, it didn't matter.
