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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - LLVM is missing loop splitting"
href="https://bugs.llvm.org/show_bug.cgi?id=36990">36990</a>
</td>
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<tr>
<th>Summary</th>
<td>LLVM is missing loop splitting
</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>Windows NT
</td>
</tr>
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<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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>evstupac@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Even for a very simple case:
int foo(int *a, int n, int m) {
int s = 0;
int i;
for (i = 0; i < 1024; i++)
if (i != 512)
s += a[i];
return s;
}
llvm is unable to split loop into 2:
int foo(int *a, int n, int m) {
int s = 0;
int i;
for (i = 0; i < 512; i++)
s += a[i];
for (i = 513; i < 1024; i++)
s += a[i];
return s;
}
Generated IR:
; <label>:4: ; preds = %12, %3
%5 = phi i64 [ 0, %3 ], [ %14, %12 ]
%6 = phi i32 [ 0, %3 ], [ %13, %12 ]
%7 = icmp eq i64 %5, 512
br i1 %7, label %12, label %8
; <label>:8: ; preds = %4
%9 = getelementptr inbounds i32, i32* %0, i64 %5
%10 = load i32, i32* %9, align 4, !tbaa !2
%11 = add nsw i32 %10, %6
br label %12
; <label>:12: ; preds = %4, %8
%13 = phi i32 [ %11, %8 ], [ %6, %4 ]
%14 = add nuw nsw i64 %5, 1
%15 = icmp eq i64 %14, 1024
br i1 %15, label %16, label %4, !llvm.loop !6
; <label>:16: ; preds = %12
ret i32 %13</pre>
</div>
</p>
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