------- Comment #2 from rguenther at suse dot de 2010-09-09 08:43 -------
Subject: Re: New: Missed devirtualization
On Thu, 9 Sep 2010, hubicka at gcc dot gnu dot org wrote:
> The following testcase taken from testsuite (and many others):
> // PR 14535
> // { dg-do run }
> // { dg-options "-O -finline" }
> //
> // Original test case failure required that Raiser constructor be inlined.
>
> extern "C" void abort();
> bool destructor_called = false;
>
> struct B {
> virtual void Run(){};
> };
>
> struct D : public B {
> virtual void Run()
> {
> struct O {
> ~O() { destructor_called = true; };
> } o;
>
> struct Raiser {
> Raiser() throw( int ) {throw 1;};
> } raiser;
> };
> };
>
> int main() {
> try {
> D d;
> static_cast<B&>(d).Run();
> } catch (...) {}
>
> if (!destructor_called)
> abort ();
> }
>
> leads to following in .optimized dump:
> <bb 2>:
> MEM[(struct B *)&d]._vptr.B = &_ZTV1B[2];
> d.D.2108._vptr.B = &_ZTV1D[2];
> D.2210_2 = _ZTV1D[2];
> OBJ_TYPE_REF(D.2210_2;&d.D.2108->0) (&d.D.2108);
>
> Obviously OBJ_TYPE_REF can be optimized here since we know the
> virtual table. Why it is missed?
>
> I run into it because my new folding code is actually smart enough to lead to:
> int (*__vtbl_ptr_type) (void)
>
> void D::<T400> (struct D *)
>
> D.2210_2 = Run;
>
> The error comes because we pick from initializer of VTBL the following
> ADDR_EXPR:
> <addr_expr 0x7ffff7ec8b10
> type <pointer_type 0x7ffff6b7db28 __vtbl_ptr_type
> type <function_type 0x7ffff6b7da80 type <integer_type 0x7ffff7edb498
> int>
> type_6 QI
> size <integer_cst 0x7ffff7ec54d8 constant 8>
> unit size <integer_cst 0x7ffff7ec5500 constant 1>
> align 8 symtab 0 alias set -1 canonical type 0x7ffff6b7da80
> pointer_to_this <pointer_type 0x7ffff6b7db28 __vtbl_ptr_type>>
> unsigned type_6 DI
> size <integer_cst 0x7ffff7ec57d0 constant 64>
> unit size <integer_cst 0x7ffff7ec57f8 constant 8>
> align 64 symtab 0 alias set -1 canonical type 0x7ffff6b7db28
> pointer_to_this <pointer_type 0x7ffff6b7dc78>>
> constant
> arg 0 <function_decl 0x7ffff6b8e500 Run
> type <method_type 0x7ffff6b9b9d8 type <void_type 0x7ffff7edbe70 void>
> type_6 QI size <integer_cst 0x7ffff7ec54d8 8> unit size
> <integer_cst 0x7ffff7ec5500 1>
> align 8 symtab 0 alias set -1 canonical type 0x7ffff6b9b9d8 method
> basetype <record_type 0x7ffff6b9b7e0 D>
> arg-types <tree_list 0x7ffff6b80af0 value <pointer_type
> 0x7ffff6b9ba80>
> chain <tree_list 0x7ffff7eed398 value <void_type
> 0x7ffff7edbe70
> void>>>
> pointer_to_this <pointer_type 0x7ffff6bab150>>
> addressable volatile asm_written used public static weak autoinline
> virtual decl_5 QI file /home/jh/a.C line 15 col 18 align 16 context
> <record_type 0x7ffff6b9b7e0 D> initial <error_mark 0x7ffff7ecdb28>
> arguments <parm_decl 0x7ffff7ece990 this type <pointer_type
> 0x7ffff6b9bb28>
> readonly unsigned DI file /home/jh/a.C line 15 col 22 size
> <integer_cst 0x7ffff7ec57d0 64> unit size <integer_cst 0x7ffff7ec57f8 8>
> align 64 context <function_decl 0x7ffff6b8e500 Run>
> (reg/f:DI 62 [ this ]) arg-type <pointer_type 0x7ffff6b9bb28>
> incoming-rtl (reg:DI 5 di [ this ])>
> result <result_decl 0x7ffff7ed0380 D.2112 type <void_type
> 0x7ffff7edbe70 void>
> ignored VOID file /home/jh/a.C line 16 col 7
> align 8 context <function_decl 0x7ffff6b8e500 Run>>
> full-name "virtual void D::Run()"
> pending-inline-info 0x7ffff6ba42a0
> (mem:QI (symbol_ref/i:DI ("_ZN1D3RunEv") [flags 0x1] <function_decl
> 0x7ffff6b8e500 Run>) [0 S1 A8])>>
>
> Note the differece in between type of address and the method RUN. This is
> what
> makes verifier unhappy. How to fix this? Should FE put there some NOP_EXPR
> somewhere? Still devirtualizing should realize this case a lot earlier.
Well - it's easy. Whoever does substitution needs to verify it can
do so. Which of course is tricky with the stupid way we do
substitute_and_fold ...
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45605
