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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [ARM] TableGen doesn't select VFNMSD"
href="https://bugs.llvm.org/show_bug.cgi?id=35926">35926</a>
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<th>Summary</th>
<td>[ARM] TableGen doesn't select VFNMSD
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>GlobalISel
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>diana.picus@linaro.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19666" name="attach_19666" title="Reproducer">attachment 19666</a> <a href="attachment.cgi?id=19666&action=edit" title="Reproducer">[details]</a></span>
Reproducer
When running
llc -mtriple arm-gnueabihf -mattr=+vfp4 vfnmsd.ll
-stop-before=expand-isel-pseudos
we get a VFNMSD instruction. If we add -global-isel, we only get a VNEGD
followed by a VFNMAD.
It seems this only happens because the code for matching the VFNMSD comes after
the one for matching VFNMAD in the match table (if we manually tinker with the
order in ARMGenGlobalISel.inc, then we can successfully select VFNMSD with
-global-isel).
The relevant patterns are in ARMInstrVFP.td:
// (fneg (fma x, (fneg y), z) -> (vfnms z, x, y)
def : Pat<(fneg (f64 (fma DPR:$Dn, (fneg DPR:$Dm), DPR:$Ddin))),
(VFNMSD DPR:$Ddin, DPR:$Dn, DPR:$Dm)>,
Requires<[HasVFP4,HasDPVFP]>;
// (fneg (fma x, y, z)) -> (vfnma z, x, y)
def : Pat<(fneg (fma (f64 DPR:$Dn), (f64 DPR:$Dm), (f64 DPR:$Ddin))),
(VFNMAD DPR:$Ddin, DPR:$Dn, DPR:$Dm)>,
Requires<[HasVFP4,HasDPVFP]>;</pre>
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