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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang will emit better code when memory is leaked"
href="https://bugs.llvm.org/show_bug.cgi?id=39731">39731</a>
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</tr>
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<th>Summary</th>
<td>clang will emit better code when memory is leaked
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<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>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tiagomacarios@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>With the code below clang will generate better code when the source
conceptually leaks memory than when it does not.
clang -std=c++2a -O3
main: # @main
mov eax, 2
ret
-std=c++2a -O3 -DNOLEAK
main: # @main
push r14
push rbx
push rax
mov edi, 24
call operator new(unsigned long)
mov r14, rax
mov dword ptr [rax], 0
xorps xmm0, xmm0
movups xmmword ptr [rax + 8], xmm0
mov edi, 24
call operator new(unsigned long)
mov rbx, rax
mov dword ptr [rax], 1
xorps xmm0, xmm0
movups xmmword ptr [rax + 8], xmm0
mov qword ptr [r14 + 8], rax
mov edi, 24
call operator new(unsigned long)
mov qword ptr [rbx + 16], rax
mov rdi, rax
call operator delete(void*)
mov rdi, qword ptr [r14 + 8]
test rdi, rdi
je .LBB0_2
call operator delete(void*)
.LBB0_2:
mov rdi, r14
call operator delete(void*)
mov eax, 2
add rsp, 8
pop rbx
pop r14
ret
<a href="https://godbolt.org/z/2oQ_Ou">https://godbolt.org/z/2oQ_Ou</a>
namespace {
struct Node {
int value{};
Node* left{};
Node* right{};
constexpr Node(int i=0) noexcept : value(i) {};
};
auto constexpr left = &Node::left;
auto constexpr right = &Node::right;
template<typename T, typename... TP>
constexpr Node* traverse(T np, TP... paths) noexcept
{
return (np ->* ... ->* paths);
}
}
int main()
{
Node* const root = new Node{0};
root->left = new Node{1};
root->left->right = new Node{2};
const int val = traverse(root, left, right)->value;
#if defined(NOLEAK)
delete root->left->right;
delete root->left;
delete root;
#endif
return val;
}</pre>
</div>
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