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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Support TEST DATA CLASS instruction"
href="https://llvm.org/bugs/show_bug.cgi?id=23418">23418</a>
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<th>Summary</th>
<td>Support TEST DATA CLASS instruction
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>Other
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: SystemZ
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>uweigand@de.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>System z provides a TEST DATA CLASS instruction that could be used to
implement any of the floating-point test builtins, including isfinite,
isinf, isnan, or isnormal.
To implement that, the back-end should recognize the typical idioms
used to implement those checks and convert them into TDC primitives,
and then collect multiple such primitives when possible.
For example, __builtin_isfinite (f) is represented in LLVM IR as:
%iseq = fcmp ord double %f, 0.000000e+00
%0 = tail call double @llvm.fabs.f64(double %f)
%isinf = fcmp une double %0, 0x7FF0000000000000
%and = and i1 %iseq, %isinf
Via repeated application of the following rules:
%y = fcmp ord double %x, 0.000000e+00
--> %y = TDC %x, 0xff0
%y = fcmp une double %x, 0x7FF0000000000000
--> %y = TDC %x, 0xfdf
%y = tail call double @llvm.fabs.f64(double %x)
%z = TDC %y, %mask
--> %z = TDC %x, (%mask & 0xaaa) | ((%mask & 0xaaa) >> 1)
%y = TDC %x, %mask1
%z = TDC %x, %mask2
%t = and i1 %y %z
--> %t = TDC %x, %mask1 & %mask2
this could be simplified to:
%and = TDC %f, 0xfc0
which implements exactly the "isfinite" logic.
(The above is just a subset of rules that could be applicable for a fully
generic implementation.)
It should be possible to do this during SelectionDAG isel.</pre>
</div>
</p>
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