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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LLVM 3.8.1 compiles VMOVSD on Intel Skylake using EVEX"
href="https://llvm.org/bugs/show_bug.cgi?id=29162">29162</a>
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<th>Summary</th>
<td>LLVM 3.8.1 compiles VMOVSD on Intel Skylake using EVEX
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.8
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>other
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>release blocker
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>atlaste@yahoo.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>I've written most of the details down here:
<a href="http://stackoverflow.com/questions/39149605/whats-the-proper-way-of-calling-a-win32-64-function-from-llvm/39190281">http://stackoverflow.com/questions/39149605/whats-the-proper-way-of-calling-a-win32-64-function-from-llvm/39190281</a>
To cut to the conclusion, here's what's basically happening: The moment you
compile a program that uses floating point (f.ex. call an external method and
load a floating point constant) using the MCJIT on an Intel Skylake, it will
generate a VMOVSD instruction (which is correct).
VMOVSD is actually an AVX instruction, and encoded with VEX, will give:
C5 FB 10 08 vmovsd xmm1,qword ptr [rax]
On Intel Skylake, the emitter incorrectly assumes that EVEX is supported,
generating the corresponding EVEX encoding:
62 f1 FF 08 ... vmovsd xmm1,qword ptr [rax]
However, EVEX won't be supported until Skylake Purley in 2017, so this will
crash the program.
If you fix the issue, please let me know what code is affected.</pre>
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