Re: Beginner's Question...

Kurt Svensson wrote:
> Is it still source code reading and parsing the bottleneck or what?


I think that today in C++, the bottleneck is template expansion, at
least on the compiler that I use (MSVC++), because it has the
"inclusion" model of templates. If/when someone implements the
"export" keyword for templates, I think that something other than
templates might emerge as the culprit.


Without templates, it seems that the work of lexing/parsing/analyzing
the zillion lines of header file that are included for each source
file is clearly the big hit. This doesn't break down per-task, but I
separate it out because precompiled headers can mitigate all the tasks
associated with header file processing to some degree.


> Has not the importance of the parser (exclusive lex) speed declined lately?


I think yes, the raw recognition of tokens and syntactic patterns has
beome less important, except where the ratio of non-code-producing
header file inclusion to code-producing source file size is large (as
it often is). In a language like C++, a large amount of time is spent
managing the symbol table and the scope hierarchy, and the synactic
phase gets muddled with the semantic analysis.


The conclusion that raw lexing/syntax is unimportant is supported by
the observation that compiling 100k lines of C is about five times
faster than compiling 100k lines of C++, so the extra time is
certainly not spent on raw lexing and syntactic recognition.


john
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