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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 - abi for passing empty structures on x86 changed between recently"
href="https://bugs.llvm.org/show_bug.cgi?id=34272">34272</a>
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<th>Summary</th>
<td>abi for passing empty structures on x86 changed between recently
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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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>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>vargaz@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Take the following test case on osx:
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
#include <stdio.h>
typedef struct {
} Empty;
Empty ret_empty (int i) {
Empty e;
printf ("%d\n", i);
return e;
}
<span class="quote">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>></span >
In xcode7.3, which has clang version:
Apple LLVM version 7.3.0 (clang-703.0.29)
Running
clang -emit-llvm empty.c
generates the following:
define void @ret_empty(%struct.Empty* noalias sret %agg.result, i32 %i) #0 {
i.e. the struct is returned using a hidden parameter
In xcode8.3 and later, it generates the following:
define void @ret_empty(i32) #0 {
i.e. the return value is simply ignored.
The change seems to have been introduced by:
<a href="https://github.com/llvm-mirror/clang/commit/bc350ca21c51e341427c7f96dc21fc1bd8f73a2b">https://github.com/llvm-mirror/clang/commit/bc350ca21c51e341427c7f96dc21fc1bd8f73a2b</a>
The commit talks about the MCU abi, but the change seems to impact normal
linux/osx etc. as well, which seems to be an abi break. Was this intentional,
or is this a regression ?
For the record, gcc generates the same code as xcode7.3.</pre>
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