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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - InstSimplify: fadd (nsz op), +0 incorrectly removed"
href="https://bugs.llvm.org/show_bug.cgi?id=45778">45778</a>
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<th>Summary</th>
<td>InstSimplify: fadd (nsz op), +0 incorrectly removed
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Keywords</th>
<td>miscompilation
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nunoplopes@sapo.pt
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, regehr@cs.utah.edu, spatel+llvm@rotateright.com
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</tr></table>
<p>
<div>
<pre>Test: Transforms/InstSimplify/fast-math.ll
Summary: +0 + +0 == +0 and -0 + +0 == +0 in default rounding mode. Hence below
when %nsz is +/-0 the function returns +0 only, while the optimized function
returns +/-0.
define float @fold_fadd_cannot_be_neg0_nsz_src_x_0(float %a, float %b) {
%nsz = fmul nsz float %a, %b
%add = fadd float %nsz, 0.000000
ret float %add
}
=>
define float @fold_fadd_cannot_be_neg0_nsz_src_x_0(float %a, float %b) {
%nsz = fmul nsz float %a, %b
ret float %nsz
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
float %a = #x01e21080 (0.000000000000?)
float %b = #x00225d01 (0.000000000000?)
Source:
float %nsz = #x80000000 (-0.0)
float %add = #x00000000 (+0.0)
Target:
float %nsz = #x80000000 (-0.0)
Source value: #x00000000 (+0.0)
Target value: #x80000000 (-0.0)
<a href="https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=1ede71ade7988ad1&test=Transforms%2FInstSimplify%2Ffast-math.ll">https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=1ede71ade7988ad1&test=Transforms%2FInstSimplify%2Ffast-math.ll</a></pre>
</div>
</p>
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