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<base href="https://llvm.org/bugs/" />
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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 --- - [ppc] Missed vectorization"
href="https://llvm.org/bugs/show_bug.cgi?id=30990">30990</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[ppc] Missed vectorization
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>carrot@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The source code is:
int foo(char* ptr, int l) {
const char* const end = ptr + l;
int count = 0;
while (ptr < end) {
count += ((signed char)(*ptr) < -0x40) ? 1 : 0;
ptr++;
}
return count;
}
When compiled with options -m64 -O2, llvm unrolls the loop 12 times,
...
.LBB0_4: # %vector.body
# =>This Inner Loop Header: Depth=1
lbzu 0, 12(3)
ld 5, -160(1) # 8-byte Folded Reload
addi 7, 7, -12
lbz 20, 1(3)
lbz 19, 2(3)
lbz 18, 3(3)
lbz 14, 4(3)
cmpld 5, 7
extsb 0, 0
lbz 5, 5(3)
lbz 6, 7(3)
cmpwi 1, 0, -64
lbz 8, 9(3)
extsb 2, 20
extsb 19, 19
extsb 18, 18
extsb 20, 14
cmpwi 6, 2, -64
lbz 2, 6(3)
cmpwi 7, 19, -64
extsb 0, 5
lbz 5, 8(3)
cmpwi 5, 18, -64
isel 16, 10, 9, 24
extsb 18, 6
cmpwi 6, 20, -64
extsb 19, 2
extsb 20, 5
add 12, 16, 12
isel 14, 10, 9, 20
cmpwi 5, 19, -64
lbz 19, 10(3)
isel 2, 10, 9, 24
cmpwi 6, 18, -64
lbz 18, 11(3)
add 29, 14, 29
isel 15, 10, 9, 28
cmpwi 7, 0, -64
extsb 0, 8
add 28, 2, 28
isel 6, 10, 9, 28
cmpwi 7, 20, -64
extsb 20, 19
add 30, 15, 30
isel 5, 10, 9, 20
cmpwi 5, 0, -64
extsb 0, 18
add 27, 6, 27
isel 8, 10, 9, 24
cmpwi 6, 20, -64
add 25, 5, 25
isel 19, 10, 9, 28
cmpwi 7, 0, -64
add 24, 8, 24
isel 17, 10, 9, 4
add 22, 19, 22
isel 18, 10, 9, 20
add 11, 17, 11
isel 20, 10, 9, 24
add 26, 18, 26
isel 0, 10, 9, 28
add 23, 20, 23
add 21, 0, 21
bne 0, .LBB0_4
...
// the rest iterations
GCC can vectorize the loop:
...
.L4:
sldi 5,7,4
addi 7,7,1
lxvd2x 33,8,5
xxpermdi 33,33,33,2
vcmpgtsb 1,2,1
xxsel 33,35,36,33
vperm 12,1,5,7
vperm 1,1,5,8
vperm 6,12,0,9
vperm 12,12,0,10
vperm 11,1,0,9
vadduwm 6,6,13
vperm 13,1,0,10
vadduwm 12,12,6
vadduwm 12,11,12
vadduwm 13,13,12
bdnz .L4
...
// the rest iterations
In one of our internal testcase, llvm version is 2.7x times slower than gcc on
power8.</pre>
</div>
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