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Re: [C++ patch] Set attributes for C++ runtime library calls
- From: Gabriel Dos Reis <gdr at integrable-solutions dot net>
- To: Alexander Monakov <amonakov at ispras dot ru>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>
- Date: Thu, 22 Aug 2013 10:54:54 -0500
- Subject: Re: [C++ patch] Set attributes for C++ runtime library calls
- References: <20130822131927 dot GA18084 at kam dot mff dot cuni dot cz> <CAAiZkiDRZj-Fzy2+zUo9Z2B5ShvJ6K_duNyX1SKfrEZeX1NNZQ at mail dot gmail dot com> <alpine dot LNX dot 2 dot 00 dot 1308221836460 dot 30125 at monopod dot intra dot ispras dot ru> <20130822152111 dot GB19256 at kam dot mff dot cuni dot cz> <alpine dot LNX dot 2 dot 00 dot 1308221932570 dot 30125 at monopod dot intra dot ispras dot ru>
On Thu, Aug 22, 2013 at 10:38 AM, Alexander Monakov <amonakov@ispras.ru> wrote:
> On Thu, 22 Aug 2013, Jan Hubicka wrote:
>
>> > On Thu, 22 Aug 2013, Gabriel Dos Reis wrote:
>> > > > - I would like to recall issue if we can make NEW_EXPR annotated with
>> > > > MALLOC attribute. Without it, it is basically impossible to track
>> > > > any dynamically allocated objects in the middle-end
>> > >
>> > > operator new is replaceable by user program.
>> >
>> > But so is malloc? As I understand, the reason why "malloc" attribute is not
>> > applicable to operator new is "placement new", which returns aliased memory.
>>
>> placement new is optimized to nothing, so it should not affect anything here.
>
> Which means you cannot annotate NEW_EXPR with attribute malloc when
> -fno-inline is in effect, right? Because then placement new is no longer
> optimized out. Testcase, compile with -O2 -fno-inline -fno-ipa-sra:
>
> #include <new>
> int foo(void *c)
> {
> return *(new (c) int);
> }
This should be a C++ front-end bug. The specific operator new
from <new> used in this placement-new should be folded,
even if -fno-inline. Jason, is this something easily fixable?
After overload resolution, we know exactly which operator new
we are picking, and we know it is the one coming from the
implementation with its definition. So we should be good to go.
-- Gaby