[LLVMdev] Proposal: Adding aligned instruction bundle support to MC

[Greg Fitzgerald]

>>> groups of instructions between .bundle_lock and
>>> .bundle_unlock directives cannot cross a bundle boundary
>>
>> Can this be relaxed to:  A data instruction cannot fall on a bundle
>> boundary.  ?
>
> I'm not sure what you mean, can you elaborate?

Nevermind, what I suggested was not strict enough.  I see now that the
purpose of unlock/lock is to prevent particular instructions from landing
on the bundle boundary.  For example, around a 'bic' and an indirect
branch, where the compiler inserted the bic to make the branch safe.

-Greg



On Thu, Dec 6, 2012 at 12:25 PM, Eli Bendersky <eliben at google.com> wrote:

> On Thu, Dec 6, 2012 at 11:59 AM, Greg Fitzgerald <garious at gmail.com>
> wrote:
> > Maybe I'm jumping the gun, but some initial thoughts after browsing the
> MC
> > layer changes:
> >
>
> Greg, it's great to have early comments on this.
>
> > * .bundle_align_start  -> .bundle_align_mode N  ?
> > * .bundle_align_end -> .bundle_align_mode 0  ?
>
> The initial proposal does not cover .bundle_align{start|end} on
> purpose, to keep things simple. We do plan to add them, eventually,
> probably as attributes on .bundle_lock.
>
> > * Add unit test showing .bundle_lock/unlock can be nested.
>
> Yes.
>
> >
> > I like the way you modified the existing ARM tests to show how the
> existing
> > instructions are predicated.
>
> Thanks. When upstreaming, I should remember using the new FileCheck
> feature I recently added (variable references on the same line that
> define them) which should make matching BICs more elegant.
>
> > Overall, I think the concept of Native Client
> > is well-documented and easy to follow.  Has anyone done work to show that
> > assembly in this form can be disassembled to a memory-safe assembly
> language
> > like TAL?
> >
> >
> >> groups of instructions between .bundle_lock and
> >> .bundle_unlock directives cannot cross a bundle boundary
> >
> > Can this be relaxed to:  A data instruction cannot fall on a bundle
> > boundary.  ?
>
> I'm not sure what you mean, can you elaborate?
>
> Eli
>
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