[llvm] r195632 - X86: enable AVX2 under Haswell native compilation

PaX Team pageexec at freemail.hu
Mon Nov 25 06:50:48 PST 2013

On 25 Nov 2013 at 13:39, Tim Northover wrote:

> > one question about this code (and the i386 counterpart): why can't you just
> > specify rbx/ebx as an output register? this is how linux has always done it
> > and it works fine with gcc.
> After doing some archaeology, it seems that %ebx needs to contain the
> address of the GOT in 32-bit x86 PIC mode, which probably explains why
> there's never any question of a problem on Linux.

yes, -fpic would reserve ebx but
 - the compiler can save/restore it itself (that gcc doesn't do it is a
   deficiency in there, llvm could/should do better than that i think),
 - amd64 doesn't reserve rbx as you said.

that said, don't lose much sleep over it ;).

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