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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 - Fold AND+CMP to CMP"
href="https://bugs.llvm.org/show_bug.cgi?id=38003">38003</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Fold AND+CMP to CMP
</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,
bool sw1(int x) {
switch(x) {
case 2:
case 5:
case 6:
case 31:
return true;
default:
return false;
}
}
Clang -03
sw1(int):
add edi, -2 // why?
cmp edi, 29 // fold add + cmp to cmp edi, 31
ja .LBB0_2
mov eax, 536870937
mov ecx, edi
shr eax, cl
and eax, 1
ret
.LBB0_2:
xor eax, eax
ret
GCC 8.1 emits:
sw1(int):
xor eax, eax
cmp edi, 31
ja .L1
mov eax, 1
mov ecx, edi
sal rax, cl
test eax, 2147483752
setne al
.L1:
ret
ICC 18 (more jumps, worse code?):
sw1(int):
cmp edi, 64
jae ..B1.4
mov rax, 0x080000068
bt rax, rdi
jnc ..B1.4
mov eax, 1
ret
..B1.4:
xor eax, eax
ret</pre>
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