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String & strlen optimization, force_inline in defs.h [message #34620]

Fri, 02 December 2011 09:53

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

When strlen is intrinsic and applied to string literal, both compilers are able to replace it with constant.

That has a huge impact when we do things like

String s = "Hello ";
s << "world!";

because it is possible that we completely avoid scanning literal for its length (second command is then equivalent to Cat("world!", 6)).

Now this always worked (without me actually knowing Wink

quite well in GCC, except some String methods that did have strlen hidden in .cpp file.

Not so easy with MSC, which stubbornly refuses to inline some things and needs strlen to be activated as intrinsics.

Anyway, by combination of techniques, both compiler should be now able to optimize out strlen in most common cases.

In the process, I have added "force_inline" macro (thanks for hinting that out, Novo) to hide differences between MSC (__force_inline) and GCC (declspace(always_inline) inline).

Mirek

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Re: String & strlen optimization, force_inline in defs.h [message #34638 is a reply to message #34620]

Fri, 02 December 2011 19:57

Novo
Messages: 1358
Registered: December 2006

Ultimate Contributor

Another trick:

template <int N> 
int strlen__(const char (&s)[N]) { return N; }

Cout() << strlen__("asdf") << EOL;

Regards,
Novo

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