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<p>Correct, with a couple of nit picks.</p>
<p>Relocation isn't an optimization the collector performs. It's a
key primitive the collector is built upon. Being unable to
relocate is not an allowed state. (i.e. pinning can't be required
by the compiler)</p>
<p>When you talk about variables, that's true for the *source*
language and for the *abstract* machine before lowering. After
lowering from the abstract machine, relocations are represented in
the IR explicitly as an entirely new set of defs.</p>
<p>Philip<br>
</p>
<div class="moz-cite-prefix">On 10/20/19 6:40 PM, Yafei Liu wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMUQResJZ0-UJzOuagdFmEb4oVKOw1jbP_EL4Ep5OtGZsu+H2g@mail.gmail.com">
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<div dir="ltr">Correct me if I'm wrong:
<div>Relocation in this conversation "relocation" means GC
trying to move objects in the heap for optimization (make the
data more impact for bigger room for example), this move is
invisible to a programmer, and if a compiler support to
" relocate objects directly reachable from running code", a
variable (Foo foo) may points to a different address after a
GC happens, while a programmer could still use the name foo in
the code as if nothing happened.</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sun, Oct 20, 2019 at 4:35
AM Philip Reames via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p>Exactly this. (As the person who wrote the line in
question.) <br>
</p>
<div>On 10/18/19 8:50 AM, Hiroshi Yamauchi via llvm-dev
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif">I think
it's referring to a "moving" garbage collector (as
opposed to a "non-moving" garbage collector that never
moves/relocates objects.) The difference is that for a
moving one, all pointers need to be tracked and
potentially updated, whereas for a non-moving one,
it's sufficient that at least one pointer to a live
object is seen (when there may be other pointers to
the same object elsewhere) for correctness.</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Oct 18, 2019
at 2:12 AM Yafei Liu via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org"
target="_blank" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<p>Hi all,</p>
<p>I'm investigating on integrating a gc to my llvm
project, and when I read <a
href="http://llvm.org/docs/Statepoints.html"
rel="nofollow noreferrer"
style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;color:rgb(0,89,153)"
target="_blank" moz-do-not-send="true">this
document</a>, one sentence confused me:</p>
<blockquote>
<p
style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:inherit;vertical-align:baseline;box-sizing:inherit;clear:both">However,
for a collector which wishes to relocate objects
directly reachable from running code, a higher
standard is required.</p>
</blockquote>
<p>I don't understand what the move "relocate
objects directly reachable from running code"
trying to do.</p>
<p>For my information, the concept "relocate" means
the gc pointer refereed to a new location of an
object, for example:</p>
<p>in Java:</p>
<pre style="margin-top:0px;margin-bottom:1em;padding:12px 8px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;font-size:13px;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;background-color:rgb(239,240,241);border-radius:3px;color:rgb(36,39,41)"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;vertical-align:baseline;box-sizing:inherit;white-space:inherit">Foo foo = new Foo();
foo = new Foo(); // ---> a relocation happens
</code></pre>
<p>So can anyone explain what the "relocate objects
directly reachable from running code" trying to
do?</p>
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