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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 - Spill in LL/SC loop when using fast register allocator"
href="https://bugs.llvm.org/show_bug.cgi?id=50780">50780</a>
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<th>Summary</th>
<td>Spill in LL/SC loop when using fast register allocator
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>lkail@cn.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nemanja.i.ibm@gmail.com
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<p>
<div>
<pre>For llvm IR from pr25526
```
define {i64, i1} @foo(i64* %addr, i64 %desired, i64 %new) {
%old = cmpxchg i64* %addr, i64 %desired, i64 %new seq_cst seq_cst
ret {i64, i1} %old
}
```
Run with `llc -verify-machineinstrs -mtriple=powerpc64-ibm-aix-xcoff
-regalloc=fast < bug.ll |less`
We got spills in LL/SC loop
```
# %bb.0:
std 5, -24(1) # 8-byte Folded Spill
std 4, -16(1) # 8-byte Folded Spill
std 3, -8(1) # 8-byte Folded Spill
sync
L..BB0_1: # =>This Inner Loop Header: Depth=1
ld 4, -8(1) # 8-byte Folded Reload
ld 3, -16(1) # 8-byte Folded Reload
ldarx 4, 0, 4
cmpd 3, 4
std 4, -32(1) # 8-byte Folded Spill
bne 0, L..BB0_3
# %bb.2: # in Loop: Header=BB0_1 Depth=1
ld 3, -24(1) # 8-byte Folded Reload
ld 4, -8(1) # 8-byte Folded Reload
stdcx. 3, 0, 4
bne 0, L..BB0_1
b L..BB0_4
L..BB0_3:
ld 3, -32(1) # 8-byte Folded Reload
ld 4, -8(1) # 8-byte Folded Reload
stdcx. 3, 0, 4
```
Though it hasn't caused infinite loop yet, the size of granule hasn't specified
in POWER ISA, we should avoid spilling considering implementation of POWER ISA
might vary.</pre>
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