[LLVMdev] [BUG] Support unqualified btr, bts

Joerg Sonnenberger joerg at britannica.bec.de
Wed Jul 10 12:25:32 PDT 2013

On Wed, Jul 10, 2013 at 11:30:03AM -0700, Eli Friedman wrote:
> On Wed, Jul 10, 2013 at 11:12 AM, Ramkumar Ramachandra
> <artagnon at gmail.com> wrote:
> > Hi,
> >
> > I happened to notice that linux.git uses plenty of btr and bts
> > instructions (not btrl, btrw, btsl, btsw).  For examples, see
> > arch/x86/include/asm/bitops.h.  LLVM barfs on these due to ambiguity,
> > while GNU as is fine with them.  Surely, there must be architectures
> > where the w/l variant is unavailable?
> Both variants have existed since the Intel 386.
> That said, we should probably handle this like GNU as because the
> variants behave almost identically.  Please file a bug.

I don't consider this a bug. Just like certain FP instructions, they
*are* ambigious and there is no reason to depend on magic assembler


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