My first example is not correct --- according to the standard, the
lifetime of the temporary should be extended. The second example is an
user error.
C++ standard says this in 12.2.5:
"
The second context is when a reference is bound to a temporary. The
temporary to which the reference is
bound
Hello David,
Sorry to come so late into the discussion, but...
On 21/06/12 00:50, Xinliang David Li wrote:
> One of the most common runtime errors we have seen in gcc-4_7 is
> caused by dangling references to temporaries whole life time have
> ended
>
> e.g,
>
> const A& a = foo();
>
> or
> f
This looks fine to me, if nobody has any more objections.
Jason
Ping ..
On Wed, Jul 4, 2012 at 8:01 AM, Xinliang David Li wrote:
> Comment?
>
> David
>
> On Mon, Jul 2, 2012 at 4:30 PM, Xinliang David Li wrote:
>> I extended the patch a little so that the option can be used to set
>> multiple stack reuse levels: -fstack-reuse=[all|name_vars|none]
>>
>> all:
Comment?
David
On Mon, Jul 2, 2012 at 4:30 PM, Xinliang David Li wrote:
> I extended the patch a little so that the option can be used to set
> multiple stack reuse levels: -fstack-reuse=[all|name_vars|none]
>
> all: enable stack reuse for all local vars (named vars and compiler
> generated temp
I extended the patch a little so that the option can be used to set
multiple stack reuse levels: -fstack-reuse=[all|name_vars|none]
all: enable stack reuse for all local vars (named vars and compiler
generated temporaries) which live in memory;
name_vars: enable stack reuse only for user declared
(re-post in plain text)
Moving this to cfgexpand time is simple and it can also be extended to
handle scoped variables. However Jakub raised a good point about this
being too late as stack space overlay is not the only way to cause
trouble when the lifetime of a stack object is extended beyond the
> As do I. The intent was for Ada and every other language with things like
> temporaries and cleanups to reuse the backend constructs, so that instead
> of writing optimizers, one for each language, to instead share the
> optimizer across languages. To me, the middle end and the backend are the
On Jun 26, 2012, at 9:07 AM, Michael Matz wrote:
> I agree with Jason. TARGET_EXPR and CLEANUP_POINT_EXPR might currently be
> used only for C++, but I think they are sensible general constructs to be
> supported by the gimplifier.
As do I. The intent was for Ada and every other language with
On Tue, Jun 26, 2012 at 06:07:09PM +0200, Michael Matz wrote:
> I agree with Jason. TARGET_EXPR and CLEANUP_POINT_EXPR might currently be
> used only for C++, but I think they are sensible general constructs to be
> supported by the gimplifier.
>
> But I also think that the option to disable st
Hi,
On Tue, 26 Jun 2012, Jason Merrill wrote:
> > (the gimplifier code should be in Frontend code that lowers to GENERIC
> > really and the WITH_CLEANUP_EXPR code should be C++ frontend specific
> > ...).
>
> TARGET_EXPR has been a back-end code since the dawn of GCC version
> control; if it'
On 06/26/2012 04:28 AM, Richard Guenther wrote:
No - the fact that the flag is C++ specific but in common.opt is odd enough
and -ftemp-reuse-stack sounds very very generic - which in fact it is not,
it's a no-op in C. Is there a more formal phrase for the temporary kind that
is affected?
Not t
On Mon, Jun 25, 2012 at 6:25 PM, Xinliang David Li wrote:
> Are there any more concerns about this patch? If not, I'd like to check it in.
No - the fact that the flag is C++ specific but in common.opt is odd enough
and -ftemp-reuse-stack sounds very very generic - which in fact it is not,
it's a
Are there any more concerns about this patch? If not, I'd like to check it in.
thanks,
David
On Fri, Jun 22, 2012 at 8:51 AM, Xinliang David Li wrote:
> On Fri, Jun 22, 2012 at 2:39 AM, Richard Guenther
> wrote:
>> On Fri, Jun 22, 2012 at 11:29 AM, Jason Merrill wrote:
>>> On 06/22/2012 01:30
Yes.
Original Message
From: Richard Guenther
Sent: Fri, Jun 22, 2012 02:39 AM
To: Jason Merrill
CC: Xinliang David Li ; GCC Patches
; Michael Matz
Subject: Re: New option to turn off stack reuse for temporaries
On Fri, Jun 22, 2012 at 11:29 AM, Jason Merrill wrote
On Fri, Jun 22, 2012 at 2:39 AM, Richard Guenther
wrote:
> On Fri, Jun 22, 2012 at 11:29 AM, Jason Merrill wrote:
>> On 06/22/2012 01:30 AM, Richard Guenther wrote:
What other issues? It enables more potential code motion, but on the
other hand, causes more conservative stack reuse
On Fri, Jun 22, 2012 at 11:29 AM, Jason Merrill wrote:
> On 06/22/2012 01:30 AM, Richard Guenther wrote:
>>>
>>> What other issues? It enables more potential code motion, but on the
>>> other hand, causes more conservative stack reuse. As far I can tell,
>>> the handling of temporaries is added in
On 06/22/2012 01:30 AM, Richard Guenther wrote:
What other issues? It enables more potential code motion, but on the
other hand, causes more conservative stack reuse. As far I can tell,
the handling of temporaries is added independently after the clobber
for scoped variables are introduced. This
On Thu, Jun 21, 2012 at 8:27 PM, Xinliang David Li wrote:
> On Thu, Jun 21, 2012 at 2:21 AM, Richard Guenther
> wrote:
>> On Thu, Jun 21, 2012 at 7:28 AM, Xinliang David Li
>> wrote:
>>> I modified the documentation and it now looks like this:
>>>
>>> @item -ftemp-stack-reuse
>>> @opindex ftemp
On Thu, Jun 21, 2012 at 5:53 PM, Michael Matz wrote:
> Hi,
>
> On Thu, 21 Jun 2012, Richard Guenther wrote:
>
>> The flag is not restricted to the C++ compiler and applies to all
>> automatic variables.
>
> The use of that flag in the gimplifier (->in_cleanup_expr) makes it
> actually c++ specific
On Thu, Jun 21, 2012 at 2:21 AM, Richard Guenther
wrote:
> On Thu, Jun 21, 2012 at 7:28 AM, Xinliang David Li wrote:
>> I modified the documentation and it now looks like this:
>>
>> @item -ftemp-stack-reuse
>> @opindex ftemp_stack_reuse
>> This option enables stack space reuse for temporaries. T
On 06/21/2012 02:21 AM, Richard Guenther wrote:
The flag is not restricted to the C++ compiler and applies to all automatic
variables.
This only affects the clobbers for C++ temporary objects, not clobbers
for automatic variables going out of scope.
Also with this patch you remove code moti
Hi,
On Thu, 21 Jun 2012, Richard Guenther wrote:
> The flag is not restricted to the C++ compiler and applies to all
> automatic variables.
The use of that flag in the gimplifier (->in_cleanup_expr) makes it
actually c++ specific.
> Also even with this flag there is no guarantee we cannot fig
On Thu, Jun 21, 2012 at 7:28 AM, Xinliang David Li wrote:
> I modified the documentation and it now looks like this:
>
> @item -ftemp-stack-reuse
> @opindex ftemp_stack_reuse
> This option enables stack space reuse for temporaries. The default is on.
> The lifetime of a compiler generated temporar
OK.
Jason
I modified the documentation and it now looks like this:
@item -ftemp-stack-reuse
@opindex ftemp_stack_reuse
This option enables stack space reuse for temporaries. The default is on.
The lifetime of a compiler generated temporary is well defined by the C++
standard. When a lifetime of a temporary
The documentation needs to explain more what the option controls, and
why you might want it on or off. Other than that it looks fine.
Jason
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