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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - UBSan error negating INT64_MIN in AArch64TargetLowering::LowerSELECT_CC"
href="https://bugs.llvm.org/show_bug.cgi?id=43818">43818</a>
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<th>Summary</th>
<td>UBSan error negating INT64_MIN in AArch64TargetLowering::LowerSELECT_CC
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>9.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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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: AArch64
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>andrew@scheidecker.net
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<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, peter.smith@linaro.org, Ties.Stuij@arm.com
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<p>
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<pre>In a LLVM 9 build with -DLLVM_USE_SANITIZER=Undefined, run:
llc -march=aarch64 repro.ll
where repro.ll contains:
define i64 @0(i1) {
entry:
%1 = select i1 %0, i64 0, i64 -9223372036854775808
ret i64 %1
}
This produces the error:
<snip>/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:4867:29: runtime
error: negation of -9223372036854775808 cannot be represented in type 'int64_t'
(aka 'long'); cast to an unsigned type to negate this value to itself
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
<snip>/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:4867:29 in
It looks like the bug is still present in the tip of tree code, though I
haven't tested it. Here's the code in question:
<a href="https://github.com/llvm/llvm-project/blob/073ab70b72fa0db7d9c591f77377ef3ce88cc222/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp#L5076">https://github.com/llvm/llvm-project/blob/073ab70b72fa0db7d9c591f77377ef3ce88cc222/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp#L5076</a>
const int64_t TrueVal = CTVal->getSExtValue();
const int64_t FalseVal = CFVal->getSExtValue();
//<snip>
} else if (TrueVal == -FalseVal) {
^~~~~~~~~
FalseVal is INT64_MIN, and negating it is undefined behavior.</pre>
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