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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [ppc] slow vector load instruction"
href="https://llvm.org/bugs/show_bug.cgi?id=27897">27897</a>
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<th>Summary</th>
<td>[ppc] slow vector load instruction
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<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>Compile the following code with options
-mvsx -mcpu=power8 -O2
struct A{
char* buf;
char* end;
long long size() {
return static_cast<long long>(end - buf);
}
long long foo();
};
long long A::foo()
{
if (size() > 9 || end > buf)
return 2;
return -1;
}
Trunk llvm generates:
# BB#0: # %entry
lxvd2x 0, 0, 3 // A
xxswapd 34, 0 // B
mfvsrd 3, 0 // C
mfvsrd 4, 34 // D
sub 3, 4, 3
cmpdi 3, 9
ble 0, .LBB0_2
# BB#1: # %return
li 3, 2
blr
.LBB0_2: # %lor.lhs.false
mfvsrd 3, 0
li 12, 2
mfvsrd 4, 34
cmpld 4, 3
li 3, -1
isel 3, 12, 3, 1
blr
Note that instructions ABCD are much slower than two simple general register
load instructions.
Looks like a cost model problem.</pre>
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</p>
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