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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 DCE/loop deletion"
href="https://bugs.llvm.org/show_bug.cgi?id=52355">52355</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed DCE/loop deletion
</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>Loop Optimizer
</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>inline unsigned int
stringLen(const short* const src)
{
if (src == 0 || *src == 0) {
return 0;
} else {
const short* pszTmp = src + 1;
while (*pszTmp)
++pszTmp;
return (unsigned int)(pszTmp - src);
}
}
extern void bar();
void foo(const short* const str) {
unsigned int len = stringLen(str);
if (!len) {
bar();
}
}
LLVM:
foo(short const*): # @foo(short const*)
test rdi, rdi
je .LBB0_6
cmp word ptr [rdi], 0
je .LBB0_6
xor eax, eax
.LBB0_3: # =>This Inner Loop Header: Depth=1
cmp word ptr [rdi + rax + 2], 0
lea rax, [rax + 2]
jne .LBB0_3
shr rax
test eax, eax
je .LBB0_6
ret
.LBB0_6:
jmp bar() # TAILCALL
ICC is smarter here:
foo(short const*):
test rdi, rdi #4.16
je ..B1.4 # Prob 5% #4.16
movsx eax, WORD PTR [rdi] #4.22
test eax, eax #4.29
jne ..B1.5 # Prob 72% #4.29
..B1.4: # Preds ..B1.2 ..B1.1
jmp bar() #21.9
..B1.5: # Preds ..B1.2
ret
<a href="https://godbolt.org/z/erWa6efKa">https://godbolt.org/z/erWa6efKa</a>
#23.1</pre>
</div>
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