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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Inefficient lowering of 'musttail' call"
href="https://llvm.org/bugs/show_bug.cgi?id=23470">23470</a>
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<th>Summary</th>
<td>Inefficient lowering of 'musttail' call
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</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>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.majnemer@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>consider:
target triple = "x86_64-pc-linux"
define void @f(i8* %x) {
%bc = bitcast i8* %x to void (i8*)*
musttail call void (i8*) %bc(i8* %x)
ret void
}
running it through llc gives:
f: # @f
.cfi_startproc
# BB#0:
pushq %rax
.Ltmp0:
.cfi_def_cfa_offset 16
popq %rax
jmpq *%rdi # TAILCALL
.Lfunc_end0:
.size f, .Lfunc_end0-f
.cfi_endproc
The push/pop pair seems superfluous.</pre>
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