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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [ARM Backend]Rewinding to first LDR/VLDRD should use reverse_iterator when emitting epiloge"
href="http://llvm.org/bugs/show_bug.cgi?id=18136">18136</a>
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<th>Summary</th>
<td>[ARM Backend]Rewinding to first LDR/VLDRD should use reverse_iterator when emitting epiloge
</td>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<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>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zhaoshiz@codeaurora.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu, t.p.northover@gmail.com
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Given an MBB like this, currently LLVM stops at t2LDMIA_RET.
(gdb) call MBB.dump()
BB#52: derived from LLVM BB %return
Predecessors according to CFG: BB#0 BB#51
%SP<def,tied1> = VLDMDIA_UPD %SP<tied0>, pred:14, pred:%noreg, %D8<def>,
%D9<def>, %D10<def>, %D11<def>, %D12<def>
%SP<def,tied1> = t2LDMIA_RET %SP<tied0>, pred:14, pred:%noreg, %R4<def>,
%R5<def>, %R6<def>, %R7<def>, %R8<def>, %R9<def>, %R10<def>, %R11<def>,
%PC<def>
lib/Target/ARM/ARMFrameLowering.cpp:385
// Unwind MBBI to point to first LDR / VLDRD.
const uint16_t *CSRegs = RegInfo->getCalleeSavedRegs(&MF);
if (MBBI != MBB.begin()) {
do {
if (isPopOpcode(MBBI->getOpcode()))
FirstPop = MBBI;
--MBBI;
} while (MBBI != MBB.begin() && isCSRestore(MBBI, TII, CSRegs));
if (!isCSRestore(MBBI, TII, CSRegs))
++MBBI;
}
With MinSize attribute (-Oz), folding SP update into pop results in misaligned
register values stored in stack.
<span class="quote">> aa6: b001 add sp, #4
> aa8: ecbd 8b0a vpop {d8-d12}
> aac: e8bd 8ff0 ldmia.w sp!, {r4, r5, r6, r7, r8, r9, sl, fp, pc}</span >
becomes:
<span class="quote">> a9e: ecbd 8b0a vpop {d8-d12}
> aa2: e8bd 8ff8 ldmia.w sp!, {r3, r4, r5, r6, r7, r8, r9, sl, fp, pc}</span >
Related bug: <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [ARM Backend] Flag -Oz corrupted by folding SP update into push/pop"
href="show_bug.cgi?id=18081">http://llvm.org/bugs/show_bug.cgi?id=18081</a></pre>
</div>
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