[cfe-dev] Generated AST for implicit CXXConstructorDecl

[Mikhail Ramalho via cfe-dev]

Hello all,

I'm using libTooling to generate the AST of a given program (that will
later be translated to our own internal AST), and I just found this odd
CXXConstructorDecl for the following program:

class X
{
  public:
    X() {};

    char str[20][20][230];
};

int main(void)
{
  X x;
  X x1 = x;
  return 0;
}


The implicit constructor for X is:

CXXConstructorDecl 0x3959fd0 <line:3:7> col:7 implicit used X 'void (const
class X &) throw()' inline
|   |-ParmVarDecl 0x395a110 <col:7> col:7 used 'const class X &'
|   |-CXXCtorInitializer Field 0x3908c48 'str' 'char [20][20][230]'
|   | `-ImplicitCastExpr 0x395a6e8 <col:7> 'char' <LValueToRValue>
|   |   `-ArraySubscriptExpr 0x395a6c0 <col:7> 'const char' lvalue
|   |     |-ImplicitCastExpr 0x395a6a8 <col:7> 'const char *'
<ArrayToPointerDecay>
|   |     | `-ArraySubscriptExpr 0x395a560 <col:7> 'char const[230]' lvalue
|   |     |   |-ImplicitCastExpr 0x395a548 <col:7> 'char const (*)[230]'
<ArrayToPointerDecay>
|   |     |   | `-ArraySubscriptExpr 0x395a400 <col:7> 'char
const[20][230]' lvalue
|   |     |   |   |-ImplicitCastExpr 0x395a3e8 <col:7> 'char const
(*)[20][230]' <ArrayToPointerDecay>
|   |     |   |   | `-MemberExpr 0x395a298 <col:7> 'char
const[20][20][230]' lvalue .str 0x3908c48
|   |     |   |   |   `-DeclRefExpr 0x395a270 <col:7> 'const class X'
lvalue ParmVar 0x395a110 '' 'const class X &'
|   |     |   |   `-ImplicitCastExpr 0x395a368 <col:7> 'unsigned int'
<LValueToRValue>
|   |     |   |     `-DeclRefExpr 0x395a340 <col:7> 'unsigned int' lvalue
Var 0x395a2e0 '__i0' 'unsigned int'
|   |     |   `-ImplicitCastExpr 0x395a4c0 <col:7> 'unsigned int'
<LValueToRValue>
|   |     |     `-DeclRefExpr 0x395a498 <col:7> 'unsigned int' lvalue Var
0x395a438 '__i1' 'unsigned int'
|   |     `-ImplicitCastExpr 0x395a620 <col:7> 'unsigned int'
<LValueToRValue>
|   |       `-DeclRefExpr 0x395a5f8 <col:7> 'unsigned int' lvalue Var
0x395a598 '__i2' 'unsigned int'
|   `-CompoundStmt 0x395a748 <col:7>

Which should look this (I think):

X(const X& ref) : str(ref.str[__i0][__i1][__i2]) {}

Or maybe:

X(const X& ref) { str(ref.str[__i0][__i1][__i2]); }

(None of the above is compiled)
(If we call emit-llvm, it's translated into a memcpy)

Anyway, there are a few things missing on this AST, in my opinion:

1. No VarDecl for __i0, __i1, __i2.
2. No loop to iterate and copy the array elements (a call to memcpy would
be good as well, but I don't expect that clang will generate that).

Does anyone knows if I can generate the AST with the varDecls and the loop?
I found a method on SemaDeclCXX that seems to build a loop, it's
called buildSingleCopyAssignRecursively. It's called
by buildSingleCopyAssign, that even tries to build a memcpy.

Am I out of luck and will have to go through all the implicit
generated CXXConstructorDecls and build a loop myself or is there an
alternative?

Thank you,

-- 

Mikhail Ramalho.
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