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GCC's "-fno-strict-aliasing"? (Developers)

posted by rr  , Berlin, Germany, 18.09.2008, 11:37

> As far as I know does the C standard has a few rules about aliassing. An
> alias is e.g. if you have two pointers of different types, then C assumes
> that they can't point to the same memory. (IOW one can't be an alias of
> the other)

That's also in the docs.

> A compiler can use that to optimize and reorder statements and
> assignments.
> -fno-strict-aliasing turns of that optimization, IOW their code is dirty
> and not ANSI C compatible.

But why is, e.g., Zlib faster then, if -fno-strict-aliasing turns off that optimization?

> So it turns off a valid optimization. It is afaik a typical optimization
> that is turned globally off if "strange" things happen.

I see.

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Complete thread:

• GCC's "-fno-strict-aliasing"? - rr, 17.09.2008, 18:01 (Developers)
  • GCC's "-fno-strict-aliasing"? - marcov, 18.09.2008, 10:30
    • GCC's "-fno-strict-aliasing"? - rr, 18.09.2008, 11:37
      • GCC's "-fno-strict-aliasing"? - marcov, 18.09.2008, 13:20
    • GCC's "-fno-strict-aliasing"? - RayeR, 18.09.2008, 14:10
  • GCC's "-fno-strict-aliasing"? - rr, 25.09.2008, 16:38
    • GCC's "-fno-strict-aliasing"? - RayeR, 29.09.2008, 17:09