[LLVMbugs] [Bug 23171] New: Improper function to pointer conversion in call expression in C++

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23171

            Bug ID: 23171
           Summary: Improper function to pointer conversion in call
                    expression in C++
           Product: clang
           Version: 3.5
          Hardware: Macintosh
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: alexandermbock at gmail.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Given this code:

    void f() {
        f();
    }

clang generates this AST:

TranslationUnitDecl 0x1028254d0 <<invalid sloc>>
|-TypedefDecl 0x102825a10 <<invalid sloc>> __int128_t '__int128'
|-TypedefDecl 0x102825a70 <<invalid sloc>> __uint128_t 'unsigned __int128'
|-TypedefDecl 0x102825e30 <<invalid sloc>> __builtin_va_list '__va_list_tag
[1]'
`-FunctionDecl 0x102825ed0 <bgt.cpp:1:1, line:3:1> f 'void (void)'
  `-CompoundStmt 0x102826058 <line:1:10, line:3:1>
    `-CallExpr 0x102826030 <line:2:5, col:7> 'void'
      `-ImplicitCastExpr 0x102826018 <col:5> 'void (*)(void)'
<FunctionToPointerDecay>
        `-DeclRefExpr 0x102825fc8 <col:5> 'void (void)' lvalue Function
0x102825ed0 'f' 'void (void)'

Note the ImplicitCastExpr <FunctionToPointerDecay>.

[expr.call]/1 says:
For a call to a non-member function or to a static member function, the postfix
expression shall be either an lvalue that refers to a function (in which case
the function-to-pointer standard conversion is suppressed on the postfix
expression), or it shall have pointer to function type.

I would not expect the AST to contain a function to pointer conversion when the
standard explicitly states that one does not occur. I am not aware of any
circumstance in which this could change the observable behavior of a program,
but it complicates tool development when the AST does not match what is
expected from the standard.

Note that this does not apply to C; C11 6.5.2.2 says:
The expression that denotes the called function shall have type pointer to
function returning void or returning a complete object type other than an array
type.

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