I have a case where I think useless stores are being generated, but I
want to be sure before I file a bug. This is with gcc 4.4.3 on Ubuntu
10.04, x86-64.
I have been experimenting with returning structs from functions instead
of passing pointers to out parameters. This seems like it should be
Ian Lance Taylor iant at google.com writes:
Joshua Haberman jhaberman at gmail.com writes:
I have a case where I think useless stores are being generated, but I
want to be sure before I file a bug. This is with gcc 4.4.3 on Ubuntu
10.04, x86-64.
I concur that this is a missed
Richard Guenther richard.guenther at gmail.com writes:
On Wed, Jan 6, 2010 at 7:20 PM, Nick Stoughton nick at msbit.com
wrote:
The C1x timetable has us finishing the draft for an initial ballot this
summer (the April Florence meeting being the last chance to submit new
material). The best
Erik Trulsson ertr1013 at student.uu.se writes:
int i;
unsigned int *pui = (unsigned int*)i;
unsigned int ui = *pui;
(First I will assume that 'i' will be assigned some value, to make sure it
does not contain a trap-representation, or the assignment to 'ui' would have
undefined
Robert Dewar dewar at adacore.com writes:
In any case the gcc interpretation is clearly what's
intended in my view, so if it can be argued that the
standard is inconsistent with this interpretation (I
am unconvinced that this burden has been met), then
the conclusion is to add a clarification
Andrew Haley aph at redhat.com writes:
but
(union u*)i
is not a legal lvalue expression because the dereference is undefined
behaviour.
Your example does not contain a dereference.
You may only dereference a pointer as permitted by 6.3.2.3.
6.3.2.3 does not mention dereferencing at all;
Erik Trulsson ertr1013 at student.uu.se writes:
On Sun, Jan 03, 2010 at 05:46:48AM +, Joshua Haberman wrote:
The aliasing policies that GCC implements seem to be more strict than
what is in the C99 standard. I am wondering if this is true or whether
I am mistaken (I am not an expert
Andrew Haley aph at redhat.com writes:
On 01/03/2010 10:14 PM, Joshua Haberman wrote:
Andrew Haley aph at redhat.com writes:
6.3.2.3
A pointer to an object or incomplete type may be converted to a
pointer to a different object or incomplete type. If the resulting
pointer is not correctly
Erik Trulsson ertr1013 at student.uu.se writes:
On Mon, Jan 04, 2010 at 08:17:00PM +, Joshua Haberman wrote:
The text you quoted does not contain any shall not language about
dereferencing, so this conclusion does not follow.
It doesn't have to use any shall not language
Richard Guenther richard.guenther at gmail.com writes:
On Sun, Jan 3, 2010 at 6:46 AM, Joshua Haberman jhaberman at
gmail.com wrote:
The aliasing policies that GCC implements seem to be more strict than
what is in the C99 standard. I am wondering if this is true or whether
I am mistaken
Andrew Haley aph at redhat.com writes:
On 01/03/2010 10:53 AM, Richard Guenther wrote:
GCC follows its own documentation here, not some random
websites and maybe not the strict reading of the standard.
GCC is compatible with C99 in this regard.
I do not believe this is true. Your argument
Patrick Horgan phorgan1 at yahoo.com writes:
Since it would be hard to read this any other way, it seems then you-
maintain that you found a bug in the standard, has it been brought up to-
the committee? The latest draft I see still has that wording. Doesn't-
seem to be on the radar for C1x.
Richard Guenther richard.guenther at gmail.com writes:
On Sun, Jan 3, 2010 at 10:55 PM, Joshua Haberman jhaberman at
gmail.com wrote:
This is why perfect warnings about this issue are not possible; if we
see a downcast in isolation, we do not know if it is undoing a previous
upcast
By the way, here is one case I tested where I was surprised GCC was not
more aggressive:
extern void bar();
int foo(int *i) {
if(*i) bar();
return *i;
}
With GCC 4.4.1 -O3 (Ubuntu, x86-64) this reloads *i if bar is called. I
suppose you have to allow that either i or *i is
The aliasing policies that GCC implements seem to be more strict than
what is in the C99 standard. I am wondering if this is true or whether
I am mistaken (I am not an expert on the standard, so the latter is
definitely possible).
The relevant text is:
An object shall have its stored value
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