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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Wrong code generated for code sequence shl/ashr/trunc/ashr"
href="https://bugs.llvm.org/show_bug.cgi?id=49162">49162</a>
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<th>Summary</th>
<td>Wrong code generated for code sequence shl/ashr/trunc/ashr
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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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>carrot@google.com
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
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<pre>This bug entry is requested by @RKSimon, trunc llvm generates wrong code for
the following test case
define i32* @PRXXXXXX(i32* %base, i160* %ptr160) {
%load160 = load i160, i160* %ptr160, align 4
%shl = shl i160 %load160, 80
%ashr160 = ashr i160 %shl, 112
%trunc = trunc i160 %ashr160 to i64
%ashr64 = ashr i64 %trunc, 32
%gep = getelementptr inbounds i32, i32* %base, i64 %ashr64
ret i32* %gep
}
PRXXXXXX: # @PRXXXXXX
lea rax, [rdi - 4]
ret
Correct result should be
PRXXXXXX: # @PRXXXXXX
mov eax, dword ptr [rsi + 8]
shl eax, 16
cdqe
sar rax, 16
lea rax, [rdi + 4*rax]
ret
It is also demonstrated by <a href="https://godbolt.org/z/snajbG">https://godbolt.org/z/snajbG</a>.
It is caused by patch
<a href="https://reviews.llvm.org/rG69bc0990a9181e6eb86228276d2f59435a7fae67">https://reviews.llvm.org/rG69bc0990a9181e6eb86228276d2f59435a7fae67</a>.</pre>
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