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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 --- - cmp should be known true (via CVP?)"
href="https://llvm.org/bugs/show_bug.cgi?id=30773">30773</a>
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<th>Summary</th>
<td>cmp should be known true (via CVP?)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat cvp.c
void g(int * __attribute((aligned(256))) a, int * __attribute((aligned(256)))
b, int * __attribute((aligned(256))) c, int n) {
for (int i = 0; i < n * 16; ++i)
c[i] = a[i] + b[i];
}
$ ./clang -O2 cvp.c -S -emit-llvm -o -
define void @g(i32* nocapture readonly %a, i32* nocapture readonly %b, i32*
nocapture %c, i32 %n) local_unnamed_addr #0 {
entry:
%cmp10 = icmp sgt i32 %n, 0
br i1 %cmp10, label %for.body.preheader, label %for.cond.cleanup
for.body.preheader:
%mul = shl nsw i32 %n, 4 <--- %n is positive; %mul must be positive (nsw)
%0 = sext i32 %mul to i64
%1 = icmp sgt i64 %0, 1 <--- so this must be true
%smax = select i1 %1, i64 %0, i64 1 <--- and this shouldn't be needed
...
Is this a deficiency of correlated value propagation?</pre>
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