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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [PowerPC] could have used a CR-setting subtract"
href="https://llvm.org/bugs/show_bug.cgi?id=31176">31176</a>
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<th>Summary</th>
<td>[PowerPC] could have used a CR-setting subtract
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>; ret = x > y ? x-y : 0
define i32 @max(i32 %x, i32 %y) {
%sub = sub nsw i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%sel = select i1 %cmp, i32 %sub, i32 0
ret i32 %sel
}
$ ./llc -o - max.ll -mtriple=powerpc64 -mattr=isel
subf 5, 4, 3 <--- use "subf."
cmpw 0, 3, 4 <--- and eliminate this cmp
li 3, 0
isel 3, 5, 3, 1
blr
There's a 2nd potential bug in this example: the 'li' could be removed because
isel RT,RA,RB,BC with RA=0 treats r0 as a zero operand?</pre>
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