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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimizations for comparison with multiplications"
href="https://bugs.llvm.org/show_bug.cgi?id=38264">38264</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed optimizations for comparison with multiplications
</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>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Hello,
int f2(int x, int y, int z) {
int tmp = y--;
if (tmp * x > x * y)
return 1;
return 0;
}
Current codegen:
f2(int, int, int): # @f2(int, int, int)
lea ecx, [rsi - 1]
imul esi, edi
imul ecx, edi
xor eax, eax
cmp esi, ecx
setg al
ret
GCC:
f2(int, int, int):
xor eax, eax
test edi, edi
setg al
ret
/////////////////////
int f2(int x, int y, int z) {
if ((y-1) * x > x * y)
return 1;
return 0;
}
f2(int, int, int): # @f2(int, int, int)
lea ecx, [rsi - 1]
imul ecx, edi
imul esi, edi
xor eax, eax
cmp ecx, esi
setg al
ret
GCC:
f2(int, int, int):
mov eax, edi
shr eax, 31
ret
For unsigned case - Clang:
f2(unsigned int, unsigned int, unsigned int): # @f2(unsigned int, unsigned int,
unsigned int)
lea ecx, [rsi - 1]
imul ecx, edi
imul esi, edi
xor eax, eax
cmp ecx, esi
seta al
ret
GCC (one multiplication is eliminated):
f2(unsigned int, unsigned int, unsigned int):
sub esi, 1
xor eax, eax
imul esi, edi
add esi, edi
setc al
ret</pre>
</div>
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