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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [LTO] convert math LLVM intrinsics into finite version of libcalls"
href="https://bugs.llvm.org/show_bug.cgi?id=36879">36879</a>
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<th>Summary</th>
<td>[LTO] convert math LLVM intrinsics into finite version of libcalls
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<th>Product</th>
<td>clang
</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>Linux
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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>LLVM Codegen
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>denis.bakhvalov@intel.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre>Spawned form <a class="bz_bug_link
bz_status_NEW "
title="NEW - "[CodeGen] convert math libcalls/builtins to equivalent LLVM intrinsics" change overriding "__asm__ specifier"
href="show_bug.cgi?id=35672">https://bugs.llvm.org/show_bug.cgi?id=35672</a>
The problem mentioned above was fixed but only for non-LTO builds. For LTO
build issue still exist.
$ cat a.c
#include <math.h>
int main()
{
return exp(1.0);
}
1) Non-LTO build (notice call to '__exp_finite'):
$ clang -O0 -ffast-math a.c –lm
$ objdump -d a.out | grep "call.*exp"
400567: e8 c4 fe ff ff callq 400430 <__exp_finite@plt>
2) LTO build (notice call to 'exp'):
$ clang -O0 -flto -ffast-math a.c -lm
$ objdump -d a.out | grep "call.*exp"
400547: e8 b4 fe ff ff callq 400400 <exp@plt>
We can see that if we add ‘-flto’ we stop generating the call to finite version
of ‘exp’ function, although we could, because ‘-ffast-math’ is provided.
I debugged this issue and found the root cause. I can share the details if
someone is interested, however I don’t know how it can be fixed immediately.</pre>
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