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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Different IR if intermediate variable used for fcmp + select"
href="http://llvm.org/bugs/show_bug.cgi?id=21610">21610</a>
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<th>Summary</th>
<td>Different IR if intermediate variable used for fcmp + select
</td>
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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>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>Matthew.Arsenault@amd.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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</tr>
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>I expect these 2 functions to produce the same optimized IR, but they currently
end up using a different fcmp type.
float max_uge_f32_0(float a, float b)
{
bool cmp = !(a < b);
return cmp ? b : a;
}
float max_uge_f32_2(float a, float b)
{
return !(a < b) ? b : a;
}
clang -O3 for this produces:
define float @max_uge_f32_0(float %a, float %b) #0 {
%1 = fcmp uge float %a, %b
%2 = select i1 %1, float %b, float %a
ret float %2
}
define float @max_uge_f32_2(float %a, float %b) #0 {
%1 = fcmp olt float %a, %b
%2 = select i1 %1, float %a, float %b
ret float %2
}
I expect the second's results for the first, swapping the select operands and
using the ordered comparison. However, the first version is using the original
select order with the unordered compare.</pre>
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</p>
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