Re: Arm ldaxr / stxr loop question

Kent Dickey <kegs@provalid.com> wrote:

In article <-rKdnTO4LdoWXKj6nZ2dnZfqnPWdnZ2d@supernews.com>,
<aph@littlepinkcloud.invalid> wrote:

Kent Dickey <kegs@provalid.com> wrote:
>

Even better, let's look at the actual words for Pick Basic Dependency:
 
---
Pick Basic Dependency:
       There is a Pick Basic dependency from an effect E1 to an effect
       E2 if one of the following applies:
       1) One of the following applies:
               a) E1 is an Explicit Memory Read effect

You're right, they do seem to have forgotten to define Explicit Memory
Read effect. I'm sure they meant to.

               b) E1 is a Register Read effect
       2) One of the following applies:
               a) There is a Pick dependency through registers and memory
                       from E1 to E2
               b) E1 and E2 are the same effect

>
I don't understand this. However, here are the actual words:
>
Pick Basic dependency
>
   A Pick Basic dependency from a read Register effect or read Memory
   effect R1 to a Register effect or Memory effect E2 exists if one
   of the following applies:
>
     .   There is a Dependency through registers and memory from R1 to E2.
     .   There is an Intrinsic Control dependency from R1 to E2.
     .   There is a Pick Basic dependency from R1 to an Effect E3 and
       there is a Pick Basic dependency from E3 to E2.
>
Seems reasonable enough in context, no? It's either a data dependency,
a control dependency, or any transitive combination of them.

 
Where did you get that from?  I cannot find it in the current Arm document
DDI0487K_a_a-profile-architecture_reference_manual.pdf.  Get it from
https://developer.arm.com/documentation/ddi0487/ka/?lang=en

Err, the previous version of the same document. :-)

My text for Pick Basic dependency is a quote (where I label the lines
1a,1b, etc., where it's just bullets in the Arm document) from page B2-239,
middle of the page.
 
That sort of "summary" was exactly what I was asking for, but I don't see it,
so can you please name the page?

B2-174 in DDI0487J

I'm pretty sure there are confusing typos all through this section
(E2 and E3 getting mixed up, for example), but that Pick Basic Dependency
was a doozy.
 
It's likely the wording was better in an earlier document, I've noticed
this section getting more opaque over time.

So it seems. I think everything in DDI0487J was meant to be there in
DDI0487K, but it looks like it's all been macro-expanded and some
things fell off the page, because reasons. I believe the author of the
earlier, easier-to-read version of the Memory Model left Arm for
another company. If it's any consolation, the version of the MM before
he rewrote it was absolutely incomprehensible.

Andrew.