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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 --- - Clang optimized out two break statement from a while loop"
href="http://llvm.org/bugs/show_bug.cgi?id=16757">16757</a>
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<th>Summary</th>
<td>Clang optimized out two break statement from a while loop
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.3
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</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>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mrcool0905@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>Created <span class=""><a href="attachment.cgi?id=10960" name="attach_10960" title="example code">attachment 10960</a> <a href="attachment.cgi?id=10960&action=edit" title="example code">[details]</a></span>
example code
I have a following example function. The problem I am seeing now is that
without a return statement, clang will optimize out the break statements and
we'll never break from the while(1) and return. I've attached the example code.
bool advance() {
17 if ( mCurrent == 0 )
18 return false;
19 while( 1 )
20 {
21 mIndex ++;
22 if( mIndex > 2 )
23 {
24 mCurrent = mCurrent->next;
25 mIndex = 0;
26 }
27 if( mCurrent == 0 )
28 break;
29 if( functionReturningBool( mCurrent, mIndex ) )
30 break;
31 }
32 // warning missing return
33
34 }
Here is the disassembly:
00000000 <Iterator::advance()>:
0: e92d 4890 stmdb sp!, {r4, r7, fp, lr}
4: 4604 mov r4, r0
6: af01 add r7, sp, #4
8: 6820 ldr r0, [r4, #0]
a: 2800 cmp r0, #0
c: bf04 itt eq
e: 2000 moveq r0, #0
10: e8bd 8890 ldmiaeq.w sp!, {r4, r7, fp, pc}
14: 6862 ldr r2, [r4, #4]
16: 1c51 adds r1, r2, #1
18: 2a02 cmp r2, #2
1a: 6061 str r1, [r4, #4]
1c: 6820 ldr r0, [r4, #0]
1e: bfa2 ittt ge
20: 6800 ldrge r0, [r0, #0]
22: 2100 movge r1, #0
24: e884 0003 stmiage.w r4, {r0, r1}
28: f7ff fffe bl 0 <functionReturningBool(List*, int)>
2c: e7f2 b.n 14 <Iterator::advance()+0x14>
2e: bf00 nop</pre>
</div>
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