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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 - code compiled with -fwrapv is faster than without"
href="https://bugs.llvm.org/show_bug.cgi?id=50420">50420</a>
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</tr>
<tr>
<th>Summary</th>
<td>code compiled with -fwrapv is faster than without
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jmuizelaar@mozilla.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The following compiles to:
int f(int param) {
int result = 0;
for (int i=param; i < param + 16; i++) {
result += param;
}
return result;
}
f(int): # @f(int)
lea eax, [rdi + 15]
cmp edi, eax
cmovg eax, edi
sub eax, edi
add eax, 1
imul eax, edi
ret
with -fwrapv it becomes:
f(int): # @f(int)
mov ecx, edi
shl ecx, 4
xor eax, eax
cmp edi, 2147483632
cmovl eax, ecx
ret
with gcc it becomes:
f(int):
mov eax, edi
sal eax, 4
ret
icc and msvc compile to something similar to gcc</pre>
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</p>
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