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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 - DAGCombine incorrecly eliminates vector extension/truncation sequence"
href="https://bugs.llvm.org/show_bug.cgi?id=33368">33368</a>
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<th>Summary</th>
<td>DAGCombine incorrecly eliminates vector extension/truncation sequence
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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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>Common Code Generator Code
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>Wolfgang_Pieb@playstation.sony.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>// The following test case (derived from a randomly generated
// case) fails with -O2 (Linux):
typedef char __attribute__((ext_vector_type(2))) char2;
typedef char __attribute__((ext_vector_type(8))) char8;
extern "C" int printf(const char *, ...);
__attribute__((noinline)) void use(char2 c) {
volatile char2 cc = c;
}
__attribute__((noinline)) void test(char8 vec) {
char2 b2 = vec.zxxx.wx;
volatile char2 c2 = b2;
printf("c2:%x %x => ", c2[0], c2[1]);
if (c2[1] == 3)
printf("PASSED\n");
else
printf("FAILED\n");
use(b2);
}
int main() {
char8 vec = {1, 2, 3, 4, 5, 6, 7, 8};
test(vec);
}
// ====== end here ==========
DAGcombine incorrectly eliminates a combination of vector extension/
vector truncation because it only examines the element sizes of the
respective source and target vectors without considering the scales
of extension and truncation. The failing case extends by 2 (i8->i16)
and subsequently truncates by 8 (i64->i8), so the intermediate
operations cannot be eliminated.</pre>
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