[Bug c/61939] warn when __attribute__((aligned(x))) is ignored

2019-06-13 Thread egallager at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61939

--- Comment #4 from Eric Gallager  ---
(In reply to Daniel Santos from comment #2)
> (In reply to Vedran Miletic from comment #1)
> > #include 
> > #include 
> > float f(std::vector& A, std::vector& B)
> > {
> >   __builtin_assume_aligned(A.data(), 64);
> >   __builtin_assume_aligned(B.data(), 64);
> >   return std::inner_product(A.begin(), A.end(), B.begin(), 0.f);
> > }
> 
> You are doing it wrong. __builtin_assume_aligned() returns void* and you
> must use it's return value for it to be effective. 

Sounds like __builtin_assume_aligned() should be marked up with
__attribute__((warn_unused_result))

[Bug c/61939] warn when __attribute__((aligned(x))) is ignored

2017-07-30 Thread egallager at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61939

Eric Gallager  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2017-07-30
 CC||egallager at gcc dot gnu.org
 Ever confirmed|0   |1

--- Comment #3 from Eric Gallager  ---
I had to modify the original testcase a bit to get it to compile:

$ cat 61939.c
struct some_struct { int foo; };
void copy_something(void *p, const void *s) {
struct some_struct __attribute__((aligned(8))) *_d = p;
struct some_struct __attribute__((aligned(8))) *_s = s;
*_d = *_s;
}
$ /usr/local/bin/gcc -c -Wall -Wextra -pedantic -Wcast-align -Wattributes
61939.c
61939.c: In function ‘copy_something’:
61939.c:4:58: warning: initialization discards ‘const’ qualifier from pointer
target type [-Wdiscarded-qualifiers]
 struct some_struct __attribute__((aligned(8))) *_s = s;
  ^
$

But beyond that, yeah, confirmed. I think there's probably a duplicate around
here somewhere but I've forgotten the number already...

[Bug c/61939] warn when __attribute__((aligned(x))) is ignored

2016-10-19 Thread daniel.santos at pobox dot com 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61939

--- Comment #2 from Daniel Santos  ---
(In reply to Vedran Miletic from comment #1)
> #include 
> #include 
> float f(std::vector& A, std::vector& B)
> {
>   __builtin_assume_aligned(A.data(), 64);
>   __builtin_assume_aligned(B.data(), 64);
>   return std::inner_product(A.begin(), A.end(), B.begin(), 0.f);
> }

You are doing it wrong. __builtin_assume_aligned() returns void* and you must
use it's return value for it to be effective. So your code should be something
like this:

float f(std::vector& A, std::vector& B)
{
  float *a_data = __builtin_assume_aligned(A.data(), 64);
  float *b_data = __builtin_assume_aligned(B.data(), 64);
  return std::inner_product(a_data, b_data, B.begin(), 0.f);
}

Of course, this assumes that the buffer that your vector<> implementation
supplies is 64 byte aligned.

[Bug c/61939] warn when __attribute__((aligned(x))) is ignored

2016-10-19 Thread rivanvx at gmail dot com 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61939

Vedran Miletic  changed:

   What|Removed |Added

 CC||rivanvx at gmail dot com

--- Comment #1 from Vedran Miletic  ---
Confirmed still occurs in 6.2.1 on the following C++ code:

#include 
#include 
float f(std::vector& A, std::vector& B)
{
  __builtin_assume_aligned(A.data(), 64);
  __builtin_assume_aligned(B.data(), 64);
  return std::inner_product(A.begin(), A.end(), B.begin(), 0.f);
}

Compiled using -O3 -ffast-math -mavx2.