[LLVMdev] Stange behavior in fp arithmetics on x86 (bug possibly)

[Craig Topper]

r198756 seems to be related too. That would explain why the difference
appears in 3.5 relative to 3.4.

On Thu, Oct 9, 2014 at 11:48 PM, Stephen Checkoway <s at pahtak.org> wrote:

>
> On Oct 7, 2014, at 2:26 PM, Tim Northover <t.p.northover at gmail.com> wrote:
>
> > Hi Dmitry,
> >
> > On 7 October 2014 10:50, Dmitry Borisenkov <d.borisenkov at samsung.com>
> wrote:
> >> fpfail.s:26: Error: invalid instruction suffix for `ret'
> >>
> >> I downloaded Intel manual and haven’t found any mention of retl
> instruction,
> >
> > "retl" is the AT&T syntax for the normal "ret" instruction in the
> > Intel manual, which makes it mostly undocumented.
>
> Are you sure about that? I don't recall ever seeing retl before. A while
> back a reference for AT&T was mentioned and, as I recall, this was the best
> anyone had <http://docs.oracle.com/cd/E19253-01/817-5477/817-5477.pdf>.
> It contains no mention of retl.
>
> This seems to be the commit that added support for it <
> http://lists.cs.uiuc.edu/pipermail/llvm-branch-commits/2010-May/003229.html
> >.
>
> I'm not sure I understand the distinction between retl/retq. x86 has 4
> return instruction (cribbing from the Intel manual):
>
> C3      RET             Near return
> CB      RET             Far return
> C2 iw   RET imm16       Near return + pop imm16 bytes
> CA iw   RET imm16       Far return + pop imm16 bytes
>
> (And I think that's been true since the 8086.)
>
> Distinguishing between near and far (e.g., ret vs. lret in AT&T or retn
> vs. retf with some other assemblers) makes sense, but what would a l or q
> suffix denote?
>
> But more to the point, even if there's a good reason to accept retl/retq
> as input, is there any reason to emit it ever?
>
> --
> Stephen Checkoway
>
>
>
>
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>



-- 
~Craig
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