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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 - Different optimizations on similar code"
href="https://bugs.llvm.org/show_bug.cgi?id=36969">36969</a>
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<th>Summary</th>
<td>Different optimizations on similar code
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>4.0
</td>
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<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>MacOS X
</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>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>lgalfaso@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I'm seeing different optimizations for these similar methods
bool add(const unsigned long long a, const unsigned long long b, unsigned long
long* to) {
*to = a + b;
return a > *to;
}
bool sub(const unsigned long long a, const unsigned long long b, unsigned long
long* to) {
*to = a - b;
return a < *to;
}
The first is properly optimized to
pushq %rbp
movq %rsp, %rbp
addq %rsi, %rdi
setb %al
movq %rdi, (%rdx)
popq %rbp
retq
The second generates
pushq %rbp
movq %rsp, %rbp
movq %rdi, %rax
subq %rsi, %rax
movq %rax, (%rdx)
cmpq %rdi, %rax
seta %al
popq %rbp
retq
Instead of following the same optimization as in the first case and generating
pushq %rbp
movq %rsp, %rbp
subq %rsi, %rdi
setb %al
movq %rdi, (%rdx)
popq %rbp
retq</pre>
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