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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] DAG combine infinite loop caused by combineTruncatedArithmetic trying to truncate a bitcast of a build vector of constants"
href="https://bugs.llvm.org/show_bug.cgi?id=40891">40891</a>
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<th>Summary</th>
<td>[X86] DAG combine infinite loop caused by combineTruncatedArithmetic trying to truncate a bitcast of a build vector of constants
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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
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>craig.topper@gmail.com
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<pre>The following test case causes a DAG combine infinite loop when compiled for
avx2 in 32-bit mode
define <8 x i32> @foo(<8 x i64> %x, <4 x i64> %y) {
%a = shufflevector <4 x i64> %y, <4 x i64> <i64 12345, i64 67890, i64 13579,
i64 24680>, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
%b = and <8 x i64> %x, %a
%c = trunc <8 x i64> %b to <8 x i32>
ret <8 x i32> %c
}
We get in a fight between combienTruncatedArithmetic and
hoistLogicOpWithSameOpcodeHands.
Candidate patch here <a href="https://reviews.llvm.org/D58705">https://reviews.llvm.org/D58705</a>
Filing this bug so that ISPC which found the bug has something to point to. And
because I probably need to request an 8.0 merge</pre>
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