https://bugs.llvm.org/show_bug.cgi?id=39731
Bug ID: 39731
Summary: clang will emit better code when memory is leaked
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: tiagomacar...@gmail.com
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
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
https://godbolt.org/z/2oQ_Ou
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;
}
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