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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 - [LTO] undefined reference to global variable that was used only in asm"
href="https://bugs.llvm.org/show_bug.cgi?id=35197">35197</a>
</td>
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<th>Summary</th>
<td>[LTO] undefined reference to global variable that was used only in asm
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ilia.taraban@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This test fails at linkage with "undefined reference" with LTO:
================= nice.c ==============
int f[2];
int
main()
{
__asm {
mov f[rax], rax
}
return 0;
}
=======================================
<span class="quote">>>> clang -v</span >
clang version 6.0.0 (trunk 317339)
Target: x86_64-unknown-linux-gnu
Thread model: posix
...
<span class="quote">>>> clang -c -O0 -fasm-blocks nice.c
>>> clang -O1 nice.o</span >
But fails with -flto
<span class="quote">>>> clang -c -O0 -fasm-blocks nice.c -flto
>>> clang -O1 -flto nice.o</span >
/tmp/lto-llvm-61977c.o:ld-temp.o:function main: error: undefined reference to
'f'
clang-6.0: error: linker command failed with exit code 1 (use -v to see
invocation)
<span class="quote">>>> clang -O1 -flto nice.o -Wl,-plugin-opt,-opt-bisect-limit=1</span >
BISECT: running pass (1) Dead Global Elimination on module (ld-temp.o)
...
BISECT: NOT running pass (46) X86 LEA Fixup on function (main)
/tmp/lto-llvm-7d6d61.o:ld-temp.o:function main: error: undefined reference to
'f'
clang-6.0: error: linker command failed with exit code 1 (use -v to see
invocation)
If we look at nice.o, we'll see that we still have variable 'f' before linkage
stage:
================= nice.o.ll ===========
@f = common global [2 x i32] zeroinitializer, align 4
; Function Attrs: noinline nounwind optnone uwtable
define i32 @main() #0 {
entry:
%retval = alloca i32, align 4
store i32 0, i32* %retval, align 4
call void asm sideeffect inteldialect "mov f[rax], rax",
"~{dirflag},~{fpsr},~{flags}"() #1, !srcloc !2
ret i32 0
}
=======================================</pre>
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