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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ARMTargetLowering::isLegalAddressingMode can accept incorrect addressing modes for Thumb1 target"
href="https://bugs.llvm.org/show_bug.cgi?id=34106">34106</a>
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<th>Summary</th>
<td>ARMTargetLowering::isLegalAddressingMode can accept incorrect addressing modes for Thumb1 target
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: ARM
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</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>eastig@yandex.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This bug report is a result of investigation of performance regressions on
Cortex-M0+ and Cortex-M23 triggered by the changes:
<a href="https://reviews.llvm.org/D34583">https://reviews.llvm.org/D34583</a>
See a discussion thread
<a href="http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20170731/475927.html">http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20170731/475927.html</a>
for more information about the investigation.
The current code of ARMTargetLowering::isLegalAddressingMode:
bool ARMTargetLowering::isLegalAddressingMode(const DataLayout &DL,
const AddrMode &AM, Type *Ty,
unsigned AS, Instruction *I)
const {
EVT VT = getValueType(DL, Ty, true);
if (!isLegalAddressImmediate(AM.BaseOffs, VT, Subtarget))
return false;
// Can never fold addr of global into load/store.
if (AM.BaseGV)
return false;
switch (AM.Scale) {
case 0: // no scale reg, must be "r+i" or "r", or "i".
break;
case 1:
if (Subtarget->isThumb1Only())
return false;
LLVM_FALLTHROUGH;
default:
// ARM doesn't support any R+R*scale+imm addr modes.
if (AM.BaseOffs)
return false;
if (!VT.isSimple())
return false;
if (Subtarget->isThumb2())
return isLegalT2ScaledAddressingMode(AM, VT);
For the Thumb1 target the code returns false when AM.Scale equals 1. It returns
true when AM.Scale equals 4, for example. AM.Scale == 1 which actually means no
scaling so the Thumb1 target can accept it. Other Scale values can be accepted
by the Thumb1 target because its addressing modes do not support scaling.</pre>
</div>
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