[Bug c++/38012] New: vectorizer ignores 'restrict'

[Bug c++/38012] New: vectorizer ignores 'restrict'

[David dot Monniaux at imag dot fr]

The vectorizer ignores the 'restrict' keyword regarding two pointer
destinations, and emits a run-time aliasing text.


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           Summary: vectorizer ignores 'restrict'
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: David dot Monniaux at imag dot fr
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38012

[Bug c++/38012] vectorizer ignores 'restrict'

[David dot Monniaux at imag dot fr]

------- Comment #1 from David dot Monniaux at imag dot fr  2008-11-04 16:06 -------
Created an attachment (id=16623)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16623&action=view)
source code where va and vb are thought to be aliased

The compiler should heed that va and vb cannot point to aliased locations.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38012

[Bug middle-end/38012] vectorizer ignores 'restrict'

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-11-04 16:10 -------
restrict support is only roughly implemented.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|minor                       |enhancement
          Component|c++                         |middle-end
           Keywords|                            |alias, missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38012

[Bug middle-end/38012] vectorizer ignores 'restrict'

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-06-25 11:19 -------
  double* __restrict__ va;
  const double* __restrict__ vb;
  for(unsigned i=0; i<a.size(); i++) {
    va = &a[i];
    vb = &b[i];
    (*va) = (*vb) *coef;
  }

this only says that a[i] and b[i] do not alias in one loop iteration, it
doesn't
cover cross-iteration dependencies that the vectorizer needs.

  double* __restrict__ va = a;
  const double* __restrict__ vb = b;
  for(unsigned i=0; i<a.size(); i++) {
    va[i] = vb[i] *coef;
  }

will work.


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rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38012