[LLVMdev] endian independence

Jay Foad jay.foad at gmail.com
Mon Oct 27 03:14:48 PDT 2008

>> I'm already working on this myself. Would you be interested in having
>> this work contributed back to LLVM?
> If this were to better support target independent languages, it would
> be very useful.  If you're just trying to *reduce* the endianness
> assumptions that leak through, I don't think it's a good approach.
> There is just no way to solve this problem with C.

Yes, I can see that the llvm part of this is more straightforward and
less controversial than the llvm-gcc part. Maybe I should submit the
llvm part (since it applies to all source languages) and keep the
llvm-gcc part as a local hack.

> How do you propose to handle things like:
> struct foo {
> #ifdef __LITTLE_ENDIAN__
>   int x, y;
> #else
>   int y, x;
> #endif
> };

I can't make all C programs work regardless of target endianness. This
one will only work on little-endian:

  int x = 1;
  assert(*(char *)&x == 1);

You've just highlighted another restriction that I'll have to impose:
you shouldn't expect to be able to detect target endianness at compile

All I want is that, if you write your source code so that it doesn't
make assumptions about endianness, then the compiler and its
optimisations won't introduce any new assumptions about endianness.


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