[Bug tree-optimization/42846] New: GCC sometimes ignores information about pointer target alignment

["bredelin at ucla dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

GCC sometimes loses alignment information.

If we declare an aligned pointer type:

// These two lines work (together)
typedef real aligned_real __attribute__((aligned(16)));
typedef const aligned_real* SSE_PTR;

Then gcc generates aligned access here:

// This function uses ALIGNED accesses
real f(SSE_PTR p, SSE_PTR q,int n)
{
  real sum = 0;
  for(int i=0; i<n;i++)
    sum += p[i] * q[i];

  return sum;
}

But not here:
real f2a(const double* p_, const double* q_,int n)
{
  SSE_PTR __restrict__ p = p_;
  SSE_PTR __restrict__ q = q_;
  real sum = 0;
  for(int i=0; i<n;i++)
    sum += p[i] * q[i];

  return sum;
}

This could matter when the user know which things are aligned.

gcc version 4.5.0 20100119 (experimental) [trunk revision 156049] (Ubuntu
20100119-0ubuntu1) 

gcc-4.5 -g -c test.C -O3 -ffast-math -msse3 -mtune=barcelona
-ftree-vectorizer-verbose=4


-- 
           Summary: GCC sometimes ignores information about pointer target
                    alignment
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bredelin at ucla dot edu
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42846