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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __builtin_ia32_readeflags_u64() unnecessarily forces a frame pointer"
href="https://bugs.llvm.org/show_bug.cgi?id=47531">47531</a>
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<th>Summary</th>
<td>__builtin_ia32_readeflags_u64() unnecessarily forces a frame pointer
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>10.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Frontend
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>luto@mit.edu
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>This code:
unsigned long read_eflags(void)
{
return __builtin_ia32_readeflags_u64();
}
compiles to:
read_eflags:
pushq %rbp
movq %rsp, %rbp
pushfq
popq %rax
popq %rbp
retq
which has an unnecessary frame pointer. (I'm somewhat puzzled as to why this
happened. Sure, the redzone slot clobbered by the pushfq can't be used, but I
don't see what this has to do with a frame pointer.)
gcc generates:
read_eflags:
pushfq
popq %rax
ret</pre>
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