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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 - CTR not correctly saved for inline assembly clobbering CTR"
href="https://bugs.llvm.org/show_bug.cgi?id=47812">47812</a>
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<th>Summary</th>
<td>CTR not correctly saved for inline assembly clobbering CTR
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>11.0
</td>
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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>
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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: PowerPC
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>programmerjake@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nemanja.i.ibm@gmail.com
</td>
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<p>
<div>
<pre>The following IR is miscompiled:
<a href="https://gcc.godbolt.org/z/s5zcae">https://gcc.godbolt.org/z/s5zcae</a>
target triple = "powerpc64le-unknown-linux-gnu"
define void @f(void()* %fn) {
call void asm sideeffect "mtctr 31", "~{ctr}"()
tail call void %fn()
ret void
}
Generated Assembly (trimmed to just f's instructions, comments added):
f:
.Lfunc_gep0:
addis 2, 12, .TOC.-.Lfunc_gep0@ha
addi 2, 2, .TOC.-.Lfunc_gep0@l
mflr 0
std 0, 16(1)
stdu 1, -32(1)
std 2, 24(1)
mtctr 3
mr 12, 3
mtctr 31 # note how ctr not restored before the call on next line
bctrl
ld 2, 24(1)
addi 1, 1, 32
ld 0, 16(1)
mtlr 0
blr
This causes f to call whatever address was in r31 instead of %fn despite the
inline assembly including ctr in the clobber list.</pre>
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