<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Differences between `base+width*i` and `base+=width`"
href="https://bugs.llvm.org/show_bug.cgi?id=43835">43835</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Differences between `base+width*i` and `base+=width`
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre><a href="https://godbolt.org/z/TR-s8A">https://godbolt.org/z/TR-s8A</a>
#include <array>
#include <algorithm>
void sink(int* row);
void v0(int* data, int len, int width) {
for(int i = 0; i < len; i++) {
int *row = data + width*i;
sink(row);
}
}
void v1(int* row, int len, int width) {
for(int i = 0; i < len; i++, row+=width) {
sink(row);
}
}
In first case we get
9: ; preds = %9, %5
%10 = phi i64 [ 0, %5 ], [ %13, %9 ]
%11 = mul nsw i64 %10, %6
%12 = getelementptr inbounds i32, i32* %0, i64 %11
tail call void @_Z4sinkPi(i32* %12)
%13 = add nuw nsw i64 %10, 1
but in second:
%9 = phi i32 [ 0, %5 ], [ %11, %8 ]
%10 = phi i32* [ %0, %5 ], [ %12, %8 ]
tail call void @_Z4sinkPi(i32* %10)
%11 = add nuw nsw i32 %9, 1
%12 = getelementptr inbounds i32, i32* %10, i64 %6
I'd guess the second variant is better?
The difference is interesting.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>