<div dir="ltr"><div dir="ltr">Hi Machiel,<div><br></div><div>I have requested that 84217ad6611 be merged into the LLVM 10 release branch in <a href="http://llvm.org/PR44700">http://llvm.org/PR44700</a>. It's a low-risk fix, so I'm hopeful that it will make it in.</div><div><br></div><div>-- Lang.</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jan 24, 2020 at 8:06 AM Machiel van Hooren <<a href="mailto:jcmac@machiel.info">jcmac@machiel.info</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<p>I'm very pleased that PR40074/44337 has been squashed, great
work! This means I can now use unmodified LLVM for my application
and perhaps soon target a stable release. Will it be part of the
LLVM 10 release?</p>
<p>Machiel<br>
</p>
<div>On 24-Jan-20 04:27, Lang Hames via
llvm-dev wrote:<br>
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<div dir="ltr">Hi All,
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<div>This week I've been focused on removing
some of the blockers for people
transitioning from ORCv1 to ORCv2.</div>
<div><br>
</div>
<div>Issue #1 (<a href="http://llvm.org/PR40074" target="_blank">http://llvm.org/PR40074</a>, <a href="http://llvm.org/PR44337" target="_blank">http://llvm.org/PR44337</a>):</div>
<div><br>
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<div>When LLVM codegens floating point
constants for COFF we produce named
constant pool entries of the form
__real@<bitval>. These are stored in
COFF COMDAT sections [1] which allow
duplicate symbol definitions to be
discarded (roughly equivalent to the
concept of a weak symbol). This posed two
problems: (1) ORC had no idea about the
(rough) mapping between COMDAT and Weak,
and (2) did not support late introduction
of weak symbols via
MaterializationResponsibility::defineMaterializing.
This caused use of the same floating point
constant in multiple files to result in
duplicate definition errors for the
constant pool entries. </div>
<div><br>
</div>
<div>Both issues have been addressed in
84217ad6611, and floating point constants
should now work in COFF. If you run in to
any trouble with them please file a bug
and CC me.</div>
<div><br>
</div>
<div>Issue #2: Emulated TLS and name
mangling (raised by Geoff Levner on
llvm-dev):</div>
<div><br>
</div>
<div>Use of emulated-tls affects the name
mangling of LLVM IR symbols. For a thread
local symbol with name <Name>, when
emulated-tls is enabled we will produce at
least one emulated-tls symbol:
__emutls_v.<Name> (which must then
be linker-mangled to get the final symbol
name). If that symbol has a non-zero
initializer a second symbol will also be
produced: __emutls_t.<Name>. ORCv2
requires up-front specification of the
exact set of <i>linker-level</i> symbol
names that a module produces, so that it
can dispatch and track compiles, however
none of the existing mangling code took
emulated-tls into account. This has been
fixed in ce2207abaf9 (with follow up fixes
for the various examples I broke), and you
should now be able to use thread-locals in
ORCv2.</div>
<div><br>
</div>
<div>Besides these two bugs, I have
continued work on the big static
initializer patch. Unfortunately issue #2
interacts with it, so I have to do some
integration work before it is ready to
land, but I'm hopeful that it will be
ready some time next week.</div>
<div><br>
</div>
<div>Finally, I have added a new example
(bb7a5707ac0)to
llvm/examples/LLJITExamples:
LLJITWithObjectLinkingLayerPlugin
demonstrating how to write a custom
ObjectLinkingLayer plugin.
ObjectLinkingLayer plugins can be used to
receive and respond to events in the
linking layer, and to inspect and modify
JITLink LinkGraphs during the linking
process. ORC uses this internally to
register EH frames, but the system is
likely to be of interest to anyone who
wants low level control/visibility into
the JIT linker.</div>
<div><br>
</div>
<div>— Lang.</div>
<div><br>
</div>
<div>[1] <a href="https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#comdat-sections-object-only" target="_blank">https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#comdat-sections-object-only</a> </div>
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