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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Redundant instruction injected after the rdtsc instruction"
href="http://llvm.org/bugs/show_bug.cgi?id=20881">20881</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Redundant instruction injected after the rdtsc instruction
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>FreeBSD
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>yuri@tsoft.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>In the attached case redundant instruction "movl %eax, %eax" is generated
that isn't needed.
I think this is maybe because of the preceding assembly.
$ sh run-rdts.sh
.text
.file "rdtsc.c"
.globl do_rdtsc
.align 16, 0x90
.type do_rdtsc,@function
do_rdtsc: # @do_rdtsc
.cfi_startproc
# BB#0:
pushq %rbp
.Ltmp0:
.cfi_def_cfa_offset 16
.Ltmp1:
.cfi_offset %rbp, -16
movq %rsp, %rbp
.Ltmp2:
.cfi_def_cfa_register %rbp
#APP
rdtsc
#NO_APP
# kill: EDX<def> EDX<kill> RDX<def>
shlq $32, %rdx
movl %eax, %eax
orq %rdx, %rax
popq %rbp
retq
.Ltmp3:
.size do_rdtsc, .Ltmp3-do_rdtsc
.cfi_endproc
.ident "clang version 3.6.0 (trunk 215999)"
.section ".note.GNU-stack","",@progbits</pre>
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