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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 --- - [LoopInterchange] Calls with side effects should prevent loop interchange."
href="https://llvm.org/bugs/show_bug.cgi?id=30480">30480</a>
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<th>Summary</th>
<td>[LoopInterchange] Calls with side effects should prevent loop interchange.
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Loop Optimizer
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>mcrosier@codeaurora.org
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Given the below test case:
void foo(unsigned a);
unsigned A[100][100];
void interchange_w_call() {
for (int i = 0; i < 100; ++i)
for(int j = 0; j < 100; ++j) {
foo(A[j][i]);
A[j][i] = i * j;
}
}
The loop interchange pass will interchange this loop. However, the interchange
will change the order of the values passed to foo(). If foo() has side
effects, I believe this optimization is legal.
Compile with debug output:
clang loopinterchange.c -S -o /dev/null -O3 -mllvm -enable-loopinterchange
-mllvm -debug-only=loop-interchange
Calling populateWorklist on Func: interchange_w_call Loop: %for.cond1.preheader
Worklist size = 1
Processing LoopList of size = 2
Found 2 Loads and Stores to analyze
Found anti dependency between Src and Dst
Src: %0 = load i32, i32* %arrayidx6, align 4, !tbaa !1
Dst: store i32 %2, i32* %arrayidx6, align 4, !tbaa !1
Processing Inner Loop Id = 1 and OuterLoopId = 0
Checking if loops are tightly nested
Checking instructions in Loop header and Loop latch
Loops are perfectly nested
Loops are legal to interchange
Cost = -1
Calling Split Inner Loop
splitInnerLoopLatch done
Output of splitInnerLoopHeader InnerLoopHeaderSucc & InnerLoopHeader
splitInnerLoopHeader done
adjustLoopBranches called
Loops interchanged</pre>
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