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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Arguments containing allocas for functions that use inalloca need to be evaluated first"
href="https://llvm.org/bugs/show_bug.cgi?id=26776">26776</a>
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<th>Summary</th>
<td>Arguments containing allocas for functions that use inalloca need to be evaluated first
</td>
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<th>Product</th>
<td>clang
</td>
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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>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
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<th>Component</th>
<td>LLVM Codegen
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>rnk@google.com
</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>Consider:
int x = 10;
struct A { A(); ~A(); };
void foo(A, void*, A);
int main() {
foo(A(), (++x, _alloca(x)), A());
}
Function call arguments need to live on the top of the stack, that's just how
they work. alloca, however, lets the programmer allocate stack memory from an
expression, which can break the call frame. MSVC overcomes this problem by
evaluating arguments that contain calls to alloca before the outermost call
expression. This is legal because argument evaluation order is unsequenced. We
should do the same thing in Clang at some point.</pre>
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</p>
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