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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [x86] convert xor with SMIN to add"
href="https://bugs.llvm.org/show_bug.cgi?id=52267">52267</a>
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<th>Summary</th>
<td>[x86] convert xor with SMIN to add
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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
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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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>spatel+llvm@rotateright.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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<p>
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<pre>Based on discussion in <a href="https://reviews.llvm.org/D112085">https://reviews.llvm.org/D112085</a> :
define i32 @add_smin(i32 %x) {
%r = add i32 %x, 2147483648
ret i32 %r
}
define i32 @xor_smin(i32 %x) {
%r = xor i32 %x, 2147483648
ret i32 %r
}
These are logically equivalent:
<a href="https://alive2.llvm.org/ce/z/qV46E2">https://alive2.llvm.org/ce/z/qV46E2</a>
...and instcombine chooses 'xor' for better analysis in IR. But x86 (probably
unlike most targets), may benefit from converting it back to 'add' (for legal
integer types) because that can be lowered as LEA:
movl %edi, %eax
xorl $-2147483648, %eax ## imm = 0x80000000
vs.
leal -2147483648(%rdi), %eax</pre>
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