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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [Hexagon] Suspicious 'dead store' in SplatB pattern"
href="https://bugs.llvm.org/show_bug.cgi?id=48651">48651</a>
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<th>Summary</th>
<td>[Hexagon] Suspicious 'dead store' in SplatB pattern
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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>
</tr>
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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: Hexagon
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
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</tr>
<tr>
<th>CC</th>
<td>kparzysz@quicinc.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>def SplatB: SDNodeXForm<imm, [{
uint32_t V = N->getZExtValue();
assert(isUInt<8>(V) || V >> 8 == 0xFFFFFF);
uint32_t S = V << 24 | V << 16 | V << 8 | V;
V &= 0xFF;
return CurDAG->getTargetConstant(S, SDLoc(N), MVT::i32);
}]>;
clang static analyzer reports this as a dead store - but isn't the problem that
we need to mask V's bottom 8 bits before S 'splats' it across the 32-bits:
def SplatB: SDNodeXForm<imm, [{
uint32_t V = N->getZExtValue();
assert(isUInt<8>(V) || V >> 8 == 0xFFFFFF);
V &= 0xFF;
uint32_t S = V << 24 | V << 16 | V << 8 | V;
return CurDAG->getTargetConstant(S, SDLoc(N), MVT::i32);
}]>;</pre>
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