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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Function epilog optimization does not work"
href="https://bugs.llvm.org/show_bug.cgi?id=43077">43077</a>
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<th>Summary</th>
<td>Function epilog optimization does not work
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: ARM
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rainer.herbertz@segger.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, peter.smith@linaro.org, Ties.Stuij@arm.com
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<p>
<div>
<pre>In the ARM backend, using Thumb instructions and optimization for size
the function tryFoldSPUpdateIntoPushPop() (ARMBaseInstrInfo.cpp)
should optimize function return code like:
add sp, #4
pop {r4, r5, r6, r7, pc}
into:
pop {r3, r4, r5, r6, r7, pc}
But this never works on functions returning non-void, because in the loop
for (int i = MI->getNumOperands() - 1; i >= RegListIdx; --i) {
MachineOperand &MO = MI->getOperand(i);
RegList.push_back(MO);
if (MO.isReg() && TRI->getEncodingValue(MO.getReg()) < FirstRegEnc)
FirstRegEnc = TRI->getEncodingValue(MO.getReg());
}
the operand list contains R0 (return value) at the end (implicit killed)
and the loop ends up with FirstRegEnc = 0, which prevents the optimization.
So the last two operands in the list should be ignored somehow ??</pre>
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