[Bug tree-optimization/49730] New: loop not vectorized if inside another loop

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49730

           Summary: loop not vectorized if inside another loop
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: vincenzo.innoce...@cern.ch


I've this simple double loop (used in benchmark)
the inner loop (sloop) is not vectorized when invoked inside the longer loop
(dloop)

 c++ -Ofast -c vectdloop.cc -ftree-vectorizer-verbose=7
vectdloop.cc:9: note:   Profitability threshold = 6

vectdloop.cc:9: note: Profitability threshold is 6 loop iterations.
vectdloop.cc:9: note: LOOP VECTORIZED.
vectdloop.cc:7: note: vectorized 1 loops in function.

vectdloop.cc:20: note: not vectorized: unexpected loop form.
vectdloop.cc:16: note: vectorized 0 loops in function.


#include<cmath>

inline float fn(float x) {
  return 2.f*x+std::sqrt(x);
}

void sloop(float * __restrict__ s, float const * __restrict__ xx) {
  const int ls=16;
  for (int j=0; j < ls; ++j) {
    s[j] = fn(xx[j]);
  } 
}

int dloop(float yyy) {
  int niter = 100000;
  float x = 0.5f; yyy=0;
  const int ls=16;
  for (int i=0; i < niter; ++i) { 
    float s[ls]; float xx[ls];
    for (int j=0; j < ls; ++j) xx[j] =x+(5*(j&1));
    sloop(s,xx);
    // for (int j=0; j < ls; ++j)  s[j] = fn(xx[j]); 
    x += 1e-6f;
    for (int j=0; j < ls; ++j) yyy+=s[j];
  }
  if (yyy == 2.32132323232f) niter--; 
  return niter;
}