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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 --- - Missed induction variable optimization"
href="https://llvm.org/bugs/show_bug.cgi?id=31557">31557</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed induction variable optimization
</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>Scalar Optimizations
</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
--target=powerpc64le-grtev4-linux-gnu -m64 -O2 -mvsx -mcpu=power8
extern void bar(int);
void foo(const int* p, int n) {
for (int j = 0; j < n; ++j) {
int k = p[j];
bar(k);
}
}
I got:
clrldi 30, 4, 32
addi 4, 3, -4
.p2align 5
.LBB0_2: # %for.body
# =>This Inner Loop Header: Depth=1
lwa 3, 4(4)
addi 29, 4, 4
bl _Z3bari
nop
addi 30, 30, -1
mr 4, 29
cmpldi 30, 0
bne 0, .LBB0_2
Var j is an induction variable, it is only used to index an array, so it can be
optimized away, like following
clrldi 30, 4, 32
sldi 30, 30, 2 // *
add 30, 30, 4 // *
addi 4, 3, -4
.p2align 5
.LBB0_2: # %for.body
# =>This Inner Loop Header: Depth=1
lwa 3, 4(4)
addi 29, 4, 4
bl _Z3bari
nop
// addi 30, 30, -1
mr 4, 29
cmpld 30, 29 // *
bne 0, .LBB0_2</pre>
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