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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Redundant store to calloc'ed memory not eliminated"
href="http://llvm.org/bugs/show_bug.cgi?id=19873">19873</a>
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<th>Summary</th>
<td>Redundant store to calloc'ed memory not eliminated
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>listmail@philipreames.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>calloc returns zero initialized memory. As a result, any store of a zero value
to this memory is redundant and can be eliminated.
Here's an IR test case:
declare noalias i8* @calloc(i64, i64)
; Function Attrs: nounwind uwtable
define noalias i32* @test_store() {
%1 = tail call noalias i8* @calloc(i64 1, i64 4) #2
%2 = bitcast i8* %1 to i32*
; This store is redundant
store i32 0, i32* %2, align 4
ret i32* %2
}
This was generated from Clang 3.4 from the following C++ program:
#include <cstdlib>
extern "C"
int* test_store() {
int* a = (int*)calloc(1,sizeof(int));
a[0] = 0;
return a;
}
I have confirmed that the IR fragement above survives being run through a TOT
"opt -O3" invocation.</pre>
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</p>
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