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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 --- - Registers are moved around in do{}while(); loop"
href="https://llvm.org/bugs/show_bug.cgi?id=23202">23202</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Registers are moved around in do{}while(); loop
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>3.5
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</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>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>www.kostantinaras@yahoo.gr
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14189" name="attach_14189" title="The whole function">attachment 14189</a> <a href="attachment.cgi?id=14189&action=edit" title="The whole function">[details]</a></span>
The whole function
The loop:
do{
previous = next;
in_pos++;
*out_pos++ = previous;
if(in_pos == in_limit)
goto end;
next = *in_pos;
}while(previous != next);
is translateted with -O2 to:
.LBB0_3: # Parent Loop BB0_2 Depth=1
# => This Inner Loop Header: Depth=2
#DEBUG_VALUE: xrle_compress:out <- R14
#DEBUG_VALUE: xrle_compress:repeat <- 1
mov rax, rdi
mov rcx, rsi
mov r13, rdx
add r13, 16
mov qword ptr [rbx], rax
cmp r12, rcx
je .LBB0_4
# BB#7: # in Loop: Header=BB0_3 Depth=2
#DEBUG_VALUE: xrle_compress:out <- R14
#DEBUG_VALUE: xrle_compress:repeat <- 1
mov rdi, qword ptr [rcx]
#DEBUG_VALUE: xrle_compress:next <- RDI
lea rsi, qword ptr [rcx + 8]
cmp rax, rdi
mov rdx, rbx
mov rbx, r13
jne .LBB0_3
Notice how many mov instructions are used:</pre>
</div>
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