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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 tail cail optimization when copying arrays"
href="https://bugs.llvm.org/show_bug.cgi?id=41047">41047</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed tail cail optimization when copying arrays
</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>-03, Haswell.
void memcpy_tail_call (int *__restrict__ p, int *__restrict__ q, int N)
{
p[0] = q[N-1];
for (int i = 1; i < N; i++)
{
p[i] = q[i-1];
}
}
memcpy_tail_call(int*, int*, int): # @memcpy_tail_call(int*, int*,
int)
lea eax, [rdx - 1]
movsxd rcx, eax
mov ecx, dword ptr [rsi + 4*rcx]
mov dword ptr [rdi], ecx
cmp edx, 2
jl .LBB0_2
push rax
add rdi, 4
mov edx, eax
shl rdx, 2
call memcpy
add rsp, 8
.LBB0_2:
ret
GCC generates:
memcpy_tail_call(int*, int*, int):
movsx rax, edx
mov eax, DWORD PTR [rsi-4+rax*4]
mov DWORD PTR [rdi], eax
cmp edx, 1
jle .L3
lea eax, [rdx-2]
add rdi, 4
lea rdx, [4+rax*4]
jmp memcpy
.L3:
ret</pre>
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