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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [deadargelim] removes "this" from x86_thiscallcc"
href="https://bugs.llvm.org/show_bug.cgi?id=43160">43160</a>
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<th>Summary</th>
<td>[deadargelim] removes "this" from x86_thiscallcc
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>8.0
</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>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>CFSworks@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This is very similar to <a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - Invalid function signatures when inlining `this` into multiple parameters and there is inalloca parameters"
href="show_bug.cgi?id=38487">bug 38487</a>; my test case in fact is slightly modified
from there.
In this case, I've modified the F::k function to avoid relying on the `this`
pointer. -deadargelim removes `this`, but leaves the calling convention set to
x86_thiscallcc, so the second argument (whatever that may be) ends up shoved
into ECX.
When combined with inalloca, the following fatal error is generated:
cannot use inalloca attribute on a register parameter
However, inalloca aside, removing `this` from any calling convention that
treats `this` specially does break that calling convention. The calling
convention should either be changed (to fastcc?) or the functions with these
special calling conventions should simply have their `this` pointer left alone.
// x.cpp
// clang++ -target i386-pc-windows-msvc -O3 -c x.cpp
struct Y
{
int i;
Y();
Y(const Y&);
};
void h(Y y);
namespace {
struct F {
void k(Y y) {
y.i = 0;
h(y);
}
};
}
void foo()
{
F f;
Y y;
f.k(y);
}</pre>
</div>
</p>
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