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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - aarch64 "bfm" matching fails with known-zero bits"
href="https://bugs.llvm.org/show_bug.cgi?id=46152">46152</a>
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<th>Summary</th>
<td>aarch64 "bfm" matching fails with known-zero bits
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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>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: AArch64
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>efriedma@quicinc.com
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</tr>
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<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
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<p>
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<pre>Testcase (<a href="https://godbolt.org/z/WSTfEg">https://godbolt.org/z/WSTfEg</a>):
long test(long n, long m) {
return (n & ~15) | ((m&15));
}
long test2(long n, long m) {
return (n & ~15) | (((m<<2)&15));
}
long test3(long n, long m) {
return (n << 4) | ((m&15));
}
long test4(long n, long m) {
return (n << 4) | (((m<<2)&15));
}
test(long, long): // @test(long, long)
bfxil x0, x1, #0, #4
ret
test2(long, long): // @test2(long, long)
lsl w9, w1, #2
and x8, x0, #0xfffffffffffffff0
and x9, x9, #0xc
orr x0, x9, x8
ret
test3(long, long): // @test3(long, long)
bfi x1, x0, #4, #60
mov x0, x1
ret
test4(long, long): // @test4(long, long)
lsl w8, w1, #2
and x8, x8, #0xc
bfi x8, x0, #4, #60
mov x0, x8
ret
Somehow, the matching is getting confused; in test4, we generate an extra
"and"; in test2 we completely fail to generate the bfxil.
Tripped over this looking into a different issue; not sure how important this
is in practice.</pre>
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