DOS ain't dead - GCC's "-fno-strict-aliasing"?

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

posted by marcov, 18.09.2008, 13:20

> > 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?

Probably becuase the loop is hand tuned at a certain setting to perform maximally. Compiler reordering might work against it.

If you really want to know, do what all compiler hacks do. Find a piece of source where it matters, objdump both .o and diff.

(probably needs a small script to filter out changing assembler label numbers)

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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