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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 - Clang generates i32 type index instead of i64 for getelementptr when using structs"
href="https://bugs.llvm.org/show_bug.cgi?id=38070">38070</a>
</td>
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<th>Summary</th>
<td>Clang generates i32 type index instead of i64 for getelementptr when using structs
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<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>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>janekvoirschot@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>When using an array, GEP with i64 indices are emitted; however, when using a
struct, GEP with i32 indices are emitted.
Example:
typedef struct {
unsigned a;
unsigned b;
} structure;
unsigned f(structure s) {
return s.b;
}
Compiled with: -S -emit-llvm
Results in:
%struct.structure = type { i32, i32 }
define dso_local i32 @f(i64 %s.coerce) #0 {
entry:
%s = alloca %struct.structure, align 4
%0 = bitcast %struct.structure* %s to i64*
store i64 %s.coerce, i64* %0, align 4
%b = getelementptr inbounds %struct.structure, %struct.structure* %s, i32 0,
i32 1
%1 = load i32, i32* %b, align 4
ret i32 %1
}
Whereas using an array as follows (using the same compiler flags):
unsigned f(unsigned a[50]) {
return a[12];
}
results in:
define dso_local i32 @f(i32* %a) #0 {
entry:
%a.addr = alloca i32*, align 8
store i32* %a, i32** %a.addr, align 8
%0 = load i32*, i32** %a.addr, align 8
%arrayidx = getelementptr inbounds i32, i32* %0, i64 12
%1 = load i32, i32* %arrayidx, align 4
ret i32 %1
}</pre>
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</p>
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