<html>
    <head>
      <base href="http://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - [AArch64] Build improper vector filled with undef when constant folding vselect."
   href="http://llvm.org/bugs/show_bug.cgi?id=20396">20396</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>[AArch64] Build improper vector filled with undef when constant folding vselect.
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>new-bugs
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>new bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>kevinqindev@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Testcase:
$cat test.ll

define <8 x i16> @test() {
entry:
  %mul.i = select <8 x i1> <i1 true, i1 false, i1 false, i1 true, i1 true, i1
false, i1 false, i1 true>, <8 x i16> <i16 0, i16 undef, i16 undef, i16 0, i16
0, i16 undef, i16 undef, i16 0>, <8 x i16> zeroinitializer
  %add.i = add <8 x i16> %mul.i, <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16
1, i16 1>
  ret <8 x i16> %add.i
}

Output:
$llc -mtriple=aarch64 <test.ll

LLVM ERROR: Cannot select: 0x4d423f8: v8i16 = BUILD_VECTOR 0x4d44de8,
0x4d44ce0, 0x4d44ce0, 0x4d44de8, 0x4d44de8, 0x4d44ce0, 0x4d44ce0, 0x4d44de8
[ORD=2] [ID=10]
  0x4d44de8: i32 = Constant<0> [ID=4]
  0x4d44ce0: i32 = undef [ID=3]
  0x4d44ce0: i32 = undef [ID=3]
  0x4d44de8: i32 = Constant<0> [ID=4]
  0x4d44de8: i32 = Constant<0> [ID=4]
  0x4d44ce0: i32 = undef [ID=3]
  0x4d44ce0: i32 = undef [ID=3]
  0x4d44de8: i32 = Constant<0> [ID=4]

It seems that it's caused by the bug in DAGcombiner when doing constant fold on
expanded vselect.</pre>
        </div>
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