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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] Missing VEX_WIG from a bunch of AVX instruction definitions."
href="https://bugs.llvm.org/show_bug.cgi?id=48877">48877</a>
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<th>Summary</th>
<td>[X86] Missing VEX_WIG from a bunch of AVX instruction definitions.
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>andrea.dibiagio@gmail.com
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
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<pre>While testing the disassembler functionality using llvm-mc I found a few cases
where valid encodings were incorrectly reported as errors.
It turns out that all those problematic cases were related to instructions for
which the W bit from the VEX prefix is ignored.
---
Example 1.
VEX.NDS.128.66.0F38.WIG 2B /r
VPACKUSDW xmm1, xmm2, xmm3/m128
0xC4, 0xE2, 0xE9, 0x2B, 0x05, 0x15, 0x9D, 0x3F, 0x09 // NG
0xC4, 0xE2, 0x69, 0x2B, 0x05, 0x15, 0x9D, 0x3F, 0x09 // OK
The VEX.W is set in the NG case (byte #2 is 0xE9), and cleared in the OK case
(byte #2 is 0x69).
The definition is:
defm VPACKUSDW : sse4_pack<0x2B, "vpackusdw", v8i16, v4i32, X86Packus, VR128,
i128mem, SchedWriteShuffle.XMM, load, 0>,
VEX_4V;
It is clearly missing a VEX_WIG.
---
Other problematic cases are which are affected by the same issue are:
VEX.NDS.128.66.0F38.WIG 06 /r
VPHSUBD xmm1, xmm2, xmm3/m128
0xC4, 0xE2, 0xE9, 0x06, 0x05, 0x24, 0x78, 0xF3, 0x07 // NG
0xC4, 0xE2, 0x69, 0x06, 0x05, 0x24, 0x78, 0xF3, 0x07 // OK
VEX.128.66.0F3A.WIG 61 /r ib
VPCMPESTRI xmm1, xmm2/m128, imm8
0xC4, 0xE3, 0xE9, 0x61, 0x05, 0x00, 0x25, 0x49, 0x02, 0x60 // OK
0xC4, 0xE3, 0xF9, 0x61, 0x05, 0x00, 0x25, 0x49, 0x02, 0x60 // NG
VPCMPESTRM xmm1, xmm2/m128, imm8
VPCMPISTRI xmm1, xmm2/m128, imm8
VPCMPISTRM xmm1, xmm2/m128, imm8</pre>
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