[Bug tree-optimization/49760] New: vectorization inhibited if indices are references

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49760

           Summary: vectorization inhibited if indices are references
           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


in this simple example only the third function vectorize even if they look
semantically identical to me
c++ -Wall -ftree-vectorizer-verbose=7 -Ofast -c test/testSoA.cpp 
gcc version 4.7.0 20110528 (experimental) (GCC)

struct SoA {
  int *  __restrict__ a;
  float * __restrict__ b;
  float * __restrict__ c;
  int size;
};

struct SoB {
  int *  __restrict__ a;
  float * __restrict__ b;
  int size;
};


void foo(SoA const & in, SoB & out, int & k) {
  int N=in.size;
  for (int i=0; i!=N; ++i) {
    out.b[k] = in.a[i]+in.b[i];
    out.a[k] = in.a[i];
    ++k;
  }
}

void foo2(SoA const & in, SoB & out, int & k) {
  int j=k;
  for (int i=0; i!=in.size; ++i) {
    out.b[j] = in.a[i]+in.b[i];
    out.a[j] = in.a[i];
    ++j;
  }
  k = j;
}


void foo3(SoA const & in, SoB & out, int & k) {
  int j=k;
  int N=in.size;
  for (int i=0; i!=N; ++i) {
    out.b[j] = in.a[i]+in.b[i];
    out.a[j] = in.a[i];
    ++j;
  }
  k = j;
}

messages are

test/testSoA.cpp:17: note: not vectorized: loop contains function calls or data
references that cannot be analyzed
test/testSoA.cpp:15: note: vectorized 0 loops in function.

test/testSoA.cpp:26: note: not vectorized: number of iterations cannot be
computed.
test/testSoA.cpp:24: note: vectorized 0 loops in function.


test/testSoA.cpp:38: note: cost model: epilogue peel iters set to vf/2 because
loop iterations are unknown .
…..
test/testSoA.cpp:38: note: Profitability threshold is 5 loop iterations.
….
test/testSoA.cpp:38: note: created 5 versioning for alias checks.
test/testSoA.cpp:38: note: LOOP VECTORIZED.
test/testSoA.cpp:35: note: vectorized 1 loops in function.


I will submit a different PR for the alias checks that looks not needed to me