Re: [PATCH, i386] RTM support

[Uros Bizjak <ubizjak at gmail dot com>]

On Mon, Feb 20, 2012 at 7:57 PM, Richard Henderson <rth@redhat.com> wrote:

>>>> tempRIP = RIP + SignExtend (IMM),
>>>>
>>>> where RIP is instruction following XBEGIN instruction.
>>>
>>> So? ?.+N is generic assembler syntax, not specifying IMM=6.
>>> With "xbegin .+6" the assembler will of course encode IMM=0,
>>> because it knows that the xbegin insn is 6 bytes.
>>
>> Is the "fallback code" the insn just after the xbegin insn?
>
> Yes.
>
> If you write everything in pure assembly (or if the compiler gets
> really smart) then you can use the branch-like semantics and
> arrange for the fallback code to be completely out of line.
>
> Otherwise we ignore the branch-like feature and rely entirely on
> the data characteristics of the insn, in that %rax is modified.
> Thus the initial set of -1 and subsequent compare vs the same.

I see the logic now, somehow I have assumed the "really smart" way ;)

Other than that, testing of new headers should be added to
gcc.target/i386/sse-[12,13,14].c and g++.dg/other/i386-[2,3].c.

Thanks,
Uros.