RE: [PATCH 00/11] pragma once: treewide conversion

[David Laight]

>  (a) the traditional include guard optimization HAS NO HIDDEN SEMANTIC
> MEANING. It's a pure optimization that doesn't actually change
> anything else. If you don't do the optimization, absolutely nothing
> changes.

And if the parser is well written the optimisation is probably
irrelevant compared to the compile time.

OTOH that probably requires using mmap(), memchr('\n') to look
for line starts, a fast search for '[ ]*#' followed by else/endif
and a final horrid backwards check for a continuation line.

That optimisation will generally speed up header file processing.

	David

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