[cfe-dev] -Wunreachable-code and templates

Ted Kremenek kremenek at apple.com
Tue Jan 10 10:07:19 PST 2012

On Jan 10, 2012, at 8:46 AM, David Blaikie wrote:

> I haven't done any perf analysis yet - I was asking if there was any
> recommended approach I should be using to make such measurements.
> I'll take this answer as implying that there probably isn't much &
> I'll have a first blush at making my own ad-hoc measurements. I'll
> repost here once I have any numbers I think might be useful.

That's not quite the message I was trying to convey.  :)

As a first pass, I was wondering if you had observed anything noticeable before digging deeper.

I'd approach this as follows:

(1) Try running turning the warning on by default and run it through all of our benchmark tests, e.g. the GCC testsuite, clang tests, etc.  See if there is a performance regression there.  We regularly do this when measuring compile time regressions.

(2) Try building a few real world C++ codebases that are known to use templates (or otherwise make heavy use of C++) with this warning, e.g. Clang, Boost, Blender, Qt and see if there is a noticeable compile-time regression.

(3) While doing (2), see if the results of the warning (if any) are acceptable.

This is a fair amount of work, but it's the kind of thing we need to do to make this warning production quality.

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