<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<br>
<div class="moz-cite-prefix">On 03/16/2017 01:54 PM, Friedman, Eli
via llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:689be6b4-a619-c04a-43f6-9fc4415c01e0@codeaurora.org"
type="cite">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<div class="moz-cite-prefix">On 3/16/2017 10:51 AM, Arsenault,
Matthew via llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:CY1PR1201MB1003607AA399D6BFC0B5BE6AE2260@CY1PR1201MB1003.namprd12.prod.outlook.com"
type="cite">
<style type="text/css" style="display:none;"><!-- P {margin-top:0;margin-bottom:0;} --></style>
<div id="divtagdefaultwrapper" dir="ltr" style="font-size:12pt;
color:#000000; font-family:Calibri,Arial,Helvetica,sans-serif">
<p>LLVM makes several assumptions about address space 0.
However,</p>
<p>alloca is presently constrained to always return this
address space.</p>
<p>There's no real way to avoid using alloca, so without this</p>
<p>there is no way to opt out of these assumptions.</p>
<p><span style="font-size:12pt"><br>
</span></p>
<p><span style="font-size:12pt">The problematic assumptions
include:</span></p>
<ul>
<li><span style="font-size:12pt">That the pointer size used
for the stack is the same size as </span><span
style="font-size:12pt">the code size pointer, which is
also the maximum sized pointer.</span></li>
<li><span style="font-size:12pt">That 0 is an invalid,
non-dereferencable pointer value.</span></li>
</ul>
</div>
</blockquote>
<blockquote
cite="mid:CY1PR1201MB1003607AA399D6BFC0B5BE6AE2260@CY1PR1201MB1003.namprd12.prod.outlook.com"
type="cite">
<div id="divtagdefaultwrapper" dir="ltr" style="font-size:12pt;
color:#000000; font-family:Calibri,Arial,Helvetica,sans-serif">
<span style="font-size:12pt">These are problems for AMDGPU
because alloca is used to </span><span
style="font-size:12pt">implement the private address space,
which uses a 32-bit </span><span style="font-size:12pt">index
as the pointer value. Other pointers are 64-bit </span><span
style="font-size:12pt">and behave more like LLVM's notion of
generic address </span><span style="font-size:12pt">space.
By changing the address space used for allocas, </span><span
style="font-size:12pt">we can change our generic pointer
type to be LLVM's generic </span><span
style="font-size:12pt">pointer type which does have similar
properties.</span>
<div><br>
</div>
<div>The proposal here is to add a -A field to the datalayout
string which will specify the address space for allocas.
IRBuilder::CreateAlloca and company gain a DataLayout
argument, and some intrinsics that currently don't support
address spaces need to support them.</div>
<div><br>
</div>
</div>
</blockquote>
<br>
I think we should also include the address-space of each alloca
explicitly in textual IR. Having the type depend on the
datalayout would be confusing, because you'd need to look at the
datalayout to figure out which address-space the alloca in a
snippet of IR uses.<br>
</blockquote>
<br>
Are we talking about this syntax?<br>
<br>
%i = alloca f32, align 4, addrspace 5<br>
<br>
-Hal<br>
<br>
<blockquote
cite="mid:689be6b4-a619-c04a-43f6-9fc4415c01e0@codeaurora.org"
type="cite"> <br>
Otherwise, this seems fine.<br>
<br>
<p>-Eli<br>
</p>
<pre class="moz-signature" cols="72">--
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project</pre>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
LLVM Developers mailing list
<a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>
<a class="moz-txt-link-freetext" href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
</body>
</html>