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

posted by marcov, 18.09.2008, 10:30

> Can anyone explain GCC's -fno-strict-aliasing to me? It's used
> by QEMU. I've read the docs, but still don't have clue, when what it's for
> and it's save to use. Explanations in German preferred.

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)

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.

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

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