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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Instconsistent sdiv and srem by pow2 codegen under Oz"
href="https://bugs.llvm.org/show_bug.cgi?id=52481">52481</a>
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<th>Summary</th>
<td>Instconsistent sdiv and srem by pow2 codegen under Oz
</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>
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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>craig.topper@gmail.com
</td>
</tr>
<tr>
<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>
<div>
<pre>There seems to be an ordering issue in our handling of sdiv/srem by constant
handling under -Oz.
These two test cases produce different code just from reordering the div and
rem
int foo(int x, int *rem) {
*rem = x % 256;
return x / 256;
}
int bar(int x, int *div) {
*div = x / 256;
return x % 256;
}
foo: # @foo
mov ecx, 256
mov eax, edi
cdq
idiv ecx
mov ecx, eax
shl ecx, 8
sub edi, ecx
mov dword ptr [rsi], edi
ret
bar: # @bar
mov eax, edi
mov ecx, 256
cdq
idiv ecx
mov dword ptr [rsi], eax
mov eax, edx
ret
bar is using the remainder from the idiv, while foo is using the quotient to
compute the remainder.</pre>
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