[cfe-dev] Why isn't CXXDeleteExpr present in the AST when using the nothrow version?
Gábor Márton via cfe-dev
cfe-dev at lists.llvm.org
Thu Apr 2 08:08:58 PDT 2020
Strictly speaking, a delete expression's syntax
<https://en.cppreference.com/w/cpp/language/delete> is the following:
::(optional) delete expression
::(optional) delete [] expression
So, in the second case `fundamental_nothrow`, you do not have any delete
expression in the AST, because the code syntactically does not contain any.
Instead what you do is that you explicitly call a function, that happens to
be the `operator delete` function, so you actually have a call expression
rather than a delete expression.
Hope this helps,
Gabor
On Thu, Apr 2, 2020 at 4:43 PM Kristóf Umann <dkszelethus at gmail.com> wrote:
> Hi!
>
> I noticed that for using "regular" operator delete, the CXXDeleteExpr is
> present, and so is CXXNewExpr, but when using the nothrow version, and it
> is causing me a headache while trying to implement a deallocator event in
> the clang static analyzer. I have the following declaratations:
>
> namespace std {
> typedef __typeof__(sizeof(int)) size_t;
> struct nothrow_t {};
> extern const nothrow_t nothrow;
> } // namespace std
>
> void* operator new(std::size_t, const std::nothrow_t&) throw();
> void* operator new[](std::size_t, const std::nothrow_t&) throw();
> void operator delete(void*, const std::nothrow_t&) throw();
> void operator delete[](void*, const std::nothrow_t&) throw();
>
> void* operator new (std::size_t size, void* ptr) throw() { return ptr; };
> void* operator new[] (std::size_t size, void* ptr) throw() { return ptr; };
> void operator delete (void* ptr, void*) throw() {};
> void operator delete[] (void* ptr, void*) throw() {};
>
> In the first code example, the "regular", non-nothrow version is used:
>
> namespace fundamental {
> void f() {
> int *p = new int;
> delete p;
> }
> } // namespace fundamental
>
> namespace fundamental_array {
> void f() {
> int *p = new int[2];
> delete[] p;
> }
> } // namespace fundamental_array
>
> |-NamespaceDecl 0x1e568e0
> </home/szelethus/Documents/llvm-project/clang/test/Analysis/operator-delete-analysis-order.cpp:14:1,
> line:19:1> line:14:11 fundamental
> | `-FunctionDecl 0x1e56970 <line:15:1, line:18:1> line:15:6 f 'void ()'
> | `-CompoundStmt 0x1e56b50 <col:10, line:18:1>
> | |-DeclStmt 0x1e56ae0 <line:16:3, col:19>
> | | `-VarDecl 0x1e56a28 <col:3, col:16> col:8 used p 'int *' cinit
> | | `-CXXNewExpr 0x1e56aa8 <col:12, col:16> 'int *' Function
> 0x1e25a20 'operator new' 'void *(unsigned long)'
> | `-CXXDeleteExpr 0x1e56b30 <line:17:3, col:10> 'void' Function
> 0x1e25e00 'operator delete' 'void (void *) noexcept'
> | `-ImplicitCastExpr 0x1e56b18 <col:10> 'int *' <LValueToRValue>
> | `-DeclRefExpr 0x1e56af8 <col:10> 'int *' lvalue Var 0x1e56a28
> 'p' 'int *'
> |-NamespaceDecl 0x1e56b70 <line:21:1, line:26:1> line:21:11
> fundamental_array
> | `-FunctionDecl 0x1e56c00 <line:22:1, line:25:1> line:22:6 f 'void ()'
> | `-CompoundStmt 0x1e56e58 <col:10, line:25:1>
> | |-DeclStmt 0x1e56de8 <line:23:3, col:22>
> | | `-VarDecl 0x1e56cb8 <col:3, col:21> col:8 used p 'int *' cinit
> | | `-CXXNewExpr 0x1e56da8 <col:12, col:21> 'int *' array Function
> 0x1e25be0 'operator new[]' 'void *(unsigned long)'
> | | `-ImplicitCastExpr 0x1e56d58 <col:20> 'unsigned long'
> <IntegralCast>
> | | `-IntegerLiteral 0x1e56d20 <col:20> 'int' 2
> | `-CXXDeleteExpr 0x1e56e38 <line:24:3, col:12> 'void' array Function
> 0x1e25f68 'operator delete[]' 'void (void *) noexcept'
> | `-ImplicitCastExpr 0x1e56e20 <col:12> 'int *' <LValueToRValue>
> | `-DeclRefExpr 0x1e56e00 <col:12> 'int *' lvalue Var 0x1e56cb8
> 'p' 'int *'
>
> In the second, the nothrow version. Observe how CXXNewExpr is still
> present, but not CXXDeleteExpr.
>
> namespace fundamental_nothrow {
> void f() {
> int *s = new (std::nothrow) int;
> operator delete(s, std::nothrow);
> }
> } // namespace nontrivial_destructor
>
> namespace fundamental_array_nothrow {
> void f() {
> int *s = new (std::nothrow) int;
> operator delete(s, std::nothrow);
> }
> } // namespace nontrivial_destructor
>
> |-NamespaceDecl 0x1e59b88 <line:54:1, line:60:1> line:54:11
> fundamental_nothrow
> | `-FunctionDecl 0x1e59c18 <line:56:1, line:59:1> line:56:6 f 'void ()'
> | `-CompoundStmt 0x1e5a020 <col:10, line:59:1>
> | |-DeclStmt 0x1e59e48 <line:57:3, col:34>
> | | `-VarDecl 0x1e59cd0 <col:3, col:31> col:8 used s 'int *' cinit
> | | `-CXXNewExpr 0x1e59e08 <col:12, col:31> 'int *' Function
> 0x1e49a08 'operator new' 'void *(std::size_t, const std::nothrow_t &)
> throw()'
> | | `-DeclRefExpr 0x1e59d88 <col:17, col:22> 'const
> std::nothrow_t' lvalue Var 0x1e26360 'nothrow' 'const std::nothrow_t'
> | `-CallExpr 0x1e59fc0 <line:58:3, col:34> 'void'
> | |-ImplicitCastExpr 0x1e59fa8 <col:3, col:12> 'void (*)(void *,
> const std::nothrow_t &) throw()' <FunctionToPointerDecay>
> | | `-DeclRefExpr 0x1e59f28 <col:3, col:12> 'void (void *, const
> std::nothrow_t &) throw()' lvalue Function 0x1e49fe0 'operator delete'
> 'void (void *, const std::nothrow_t &) throw()'
> | |-ImplicitCastExpr 0x1e5a008 <col:19> 'void *' <BitCast>
> | | `-ImplicitCastExpr 0x1e59ff0 <col:19> 'int *' <LValueToRValue>
> | | `-DeclRefExpr 0x1e59eb8 <col:19> 'int *' lvalue Var 0x1e59cd0
> 's' 'int *'
> | `-DeclRefExpr 0x1e59ef8 <col:22, col:27> 'const std::nothrow_t'
> lvalue Var 0x1e26360 'nothrow' 'const std::nothrow_t'
> `-NamespaceDecl 0x1e5a040 <line:62:1, line:68:1> line:62:11
> fundamental_array_nothrow
> `-FunctionDecl 0x1e5a0d0 <line:64:1, line:67:1> line:64:6 f 'void ()'
> `-CompoundStmt 0x1e5a440 <col:10, line:67:1>
> |-DeclStmt 0x1e5a2c8 <line:65:3, col:34>
> | `-VarDecl 0x1e5a188 <col:3, col:31> col:8 used s 'int *' cinit
> | `-CXXNewExpr 0x1e5a288 <col:12, col:31> 'int *' Function
> 0x1e49a08 'operator new' 'void *(std::size_t, const std::nothrow_t &)
> throw()'
> | `-DeclRefExpr 0x1e5a240 <col:17, col:22> 'const
> std::nothrow_t' lvalue Var 0x1e26360 'nothrow' 'const std::nothrow_t'
> `-CallExpr 0x1e5a3e0 <line:66:3, col:34> 'void'
> |-ImplicitCastExpr 0x1e5a3c8 <col:3, col:12> 'void (*)(void *,
> const std::nothrow_t &) throw()' <FunctionToPointerDecay>
> | `-DeclRefExpr 0x1e5a3a8 <col:3, col:12> 'void (void *, const
> std::nothrow_t &) throw()' lvalue Function 0x1e49fe0 'operator delete'
> 'void (void *, const std::nothrow_t &) throw()'
> |-ImplicitCastExpr 0x1e5a428 <col:19> 'void *' <BitCast>
> | `-ImplicitCastExpr 0x1e5a410 <col:19> 'int *' <LValueToRValue>
> | `-DeclRefExpr 0x1e5a338 <col:19> 'int *' lvalue Var 0x1e5a188
> 's' 'int *'
> `-DeclRefExpr 0x1e5a378 <col:22, col:27> 'const std::nothrow_t'
> lvalue Var 0x1e26360 'nothrow' 'const std::nothrow_t'
>
> Is this intended? If so, why?
>
> Cheers,
> Husi
>
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