[Bug tree-optimization/49616] New: REGRESSION vectorization fails in case of runtime dimensioned vector

["vincenzo.innocente at cern dot ch" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49616

           Summary: REGRESSION vectorization fails in case of runtime
                    dimensioned vector
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


4.7 fails while 4.6.1 succeed.
Test case at the end of the message: I was not able to reduce it more (the one
that fails is at the bottom)

gcc version 4.7.0 20110702 (experimental) (GCC) 
c++ -O3 -std=c++0x -ftree-vectorizer-verbose=2 -c vectBug.cc 

vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:71: note: vectorized 2 loops in function.

vectBug.cc:35: note: not vectorized: data ref analysis failed *bs$__b_46[k_320]
= D.2547_242;

vectBug.cc:48: note: not vectorized: data ref analysis failed *bs$__b_46[k_187]
= D.2556_271;

vectBug.cc:45: note: not vectorized: data ref analysis failed *bs$__b_46[k_70]
= D.2553_262;

vectBug.cc:40: note: not vectorized: data ref analysis failed *bs$__b_46[k_317]
= D.2550_251;

vectBug.cc:35: note: LOOP VECTORIZED.
vectBug.cc:48: note: LOOP VECTORIZED.
vectBug.cc:45: note: LOOP VECTORIZED.
vectBug.cc:40: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:94: note: vectorized 12 loops in function.

while
c++ -O3 -std=c++0x -ftree-vectorizer-verbose=2 -c vectBug.cc -DFIXED

vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:71: note: vectorized 2 loops in function.

vectBug.cc:35: note: LOOP VECTORIZED.
vectBug.cc:48: note: LOOP VECTORIZED.
vectBug.cc:45: note: LOOP VECTORIZED.
vectBug.cc:40: note: LOOP VECTORIZED.
vectBug.cc:35: note: LOOP VECTORIZED.
vectBug.cc:48: note: LOOP VECTORIZED.
vectBug.cc:45: note: LOOP VECTORIZED.
vectBug.cc:40: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:94: note: vectorized 16 loops in function.

and
gcc version 4.6.1 20110520 (prerelease) (GCC) 
c++ -O3 -std=c++0x -ftree-vectorizer-verbose=2 -c vectBug.cc

vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:68: note: LOOP VECTORIZED.
vectBug.cc:71: note: vectorized 2 loops in function.

vectBug.cc:35: note: LOOP VECTORIZED.
vectBug.cc:48: note: LOOP VECTORIZED.
vectBug.cc:45: note: LOOP VECTORIZED.
vectBug.cc:40: note: LOOP VECTORIZED.
vectBug.cc:35: note: LOOP VECTORIZED.
vectBug.cc:48: note: LOOP VECTORIZED.
vectBug.cc:45: note: LOOP VECTORIZED.
vectBug.cc:40: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:16: note: LOOP VECTORIZED.
vectBug.cc:28: note: LOOP VECTORIZED.
vectBug.cc:25: note: LOOP VECTORIZED.
vectBug.cc:20: note: LOOP VECTORIZED.
vectBug.cc:94: note: vectorized 16 loops in function.

test case

cat vectBug.cc 

const int arraySize=512;

struct Bar {

  int __attribute__ ((aligned(16))) c[arraySize];
  int last;

  Bar() : last(0) { refresh();}

  void refresh();

  void loop0(int N, float * f) {
    int k=0;
    int lead = arraySize-last;
    if (N<=lead) {
      for (int i=0; i!=N; ++i) f[k++] = c[last++];
      return;
    }

    for (int i=last; i!=arraySize; ++i)  f[k++] = c[i];
    int outLoop = (N-lead)/arraySize;
    last = N -lead -  outLoop*arraySize;
    for (int j=0; j!=outLoop; ++j)  {
      refresh();
      for (int i=0; i!=arraySize; ++i) f[k++] = c[i];
    }
    refresh();
    for (int i=0; i!=last; ++i) f[k++] = c[i];
  }

  template<typename F>
  void loop(int N, F f) {
    int lead = arraySize-last;
    if (N<=lead) {
      for (int i=0; i!=N; ++i) f(c[last+i]);
      last +=N;
      return;
    }

    for (int i=last; i!=arraySize; ++i)  f(c[i]);
    int outLoop = (N-lead)/arraySize;
    last = N -lead -  outLoop*arraySize;
    for (int j=0; j!=outLoop; ++j)  {
      refresh();
      for (int i=0; i!=arraySize; ++i) f(c[i]);
    }
    refresh();
    for (int i=0; i!=last; ++i) f(c[i]);
  }

};


float __attribute__ ((aligned(16))) z[4096];
void refresh();
int j=0;


void fun(float const *, float const *, int); 


template<typename F>
inline void loop(int N, F f) {
  if (j+N>4096) {
    j=0;
    refresh();
  }
  for (int i=0; i!=N; ++i) f(z[j++]);
}

void foo(int N) {
  float __attribute__ ((aligned(16))) x[N];
  float __attribute__ ((aligned(16))) y[N];
  int k=0;
  auto xs = [&x, &k](float r) { x[k++]= 1.5f*r;};
  auto ys = [&y, &k](float r) { y[k++]= r+1.f;};


  k=0;
  loop(N,xs);
  // for (int i=0; i!=N; ++i) xs(z[j++]);
    // x[k++] = z[j++];

  k=0;
  loop(N,ys);

  //  for (int i=0; i!=N; ++i) ys(z[j++]);
  //    y[k++] = z[j++];

  fun(x,y,N);
}


void load(int N) {

float __attribute__ ((aligned(16))) a[N];
#ifndef FIXED
float __attribute__ ((aligned(16))) b[N];
#else
float __attribute__ ((aligned(16))) b[1024];
#endif

  static Bar bar;


  bar.loop0(N,a);
  bar.loop0(N,b);
  fun(a,b,N);



  int k=0;
  auto as = [&a, &k](float r) { a[k++]= 1.5f*r;};
  auto bs = [&b, &k](float r) { b[k++]= r+1.f;};

  k=0;
  bar.loop(N,as);
  k=0;
  bar.loop(N,bs);   // <=== this fail (all others ok)


  fun(a,b,N);

}