Bug 49773 - use of class data members prevent vectorization
Summary: use of class data members prevent vectorization
Status: UNCONFIRMED
Alias: None
Product: gcc
Classification: Unclassified
Component: tree-optimization (show other bugs)
Version: 4.7.0
: P3 enhancement
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: missed-optimization
Depends on:
Blocks: vectorizer
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Reported: 2011-07-18 07:19 UTC by vincenzo Innocente
Modified: 2021-07-21 02:45 UTC (History)
0 users

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Description vincenzo Innocente 2011-07-18 07:19:37 UTC
in this example below the loop in the first method does not vectorize, the second does.


struct Foo {
  float a;
  float b;

  void compute1(float * __restrict__ x, float const * __restrict__ y, int N) const;
  void compute2(float * __restrict__ x, float const * __restrict__ y, int N) const;

};

void Foo::compute1(float * __restrict__ x, float const * __restrict__ y, int N) const {
  for (int i=0; i!=N; ++i)
    x[i] = a + b*y[i];
}

void Foo::compute2(float * __restrict__ x, float const * __restrict__ y, int N) const {
  float la=a, lb=b;
  for (int i=0; i!=N; ++i)
    x[i] = la + lb*y[i];
}


test/vectClass.cpp:11: note: not vectorized: loop contains function calls or data references that cannot be analyzed
test/vectClass.cpp:10: note: vectorized 0 loops in function.
vs

test/vectClass.cpp:17: note: Profitability threshold is 5 loop iterations.
test/vectClass.cpp:17: note: LOOP VECTORIZED.
test/vectClass.cpp:15: note: vectorized 1 loops in function.
Comment 1 vincenzo Innocente 2011-07-18 14:11:11 UTC
I just upgraded to

c++ -v
Using built-in specs.
COLLECT_GCC=c++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin10.8.0/4.7.0/lto-wrapper
Target: x86_64-apple-darwin10.8.0
Configured with: ./configure --enable-languages=c,c++,fortran --enable-lto --with-build-config=bootstrap-lto CFLAGS='-O2 -ftree-vectorize -fPIC' CXXFLAGS='-O2 -fPIC -ftree-vectorize -fvisibility-inlines-hidden'
Thread model: posix
gcc version 4.7.0 20110716 (experimental) (GCC) 

and it seem to vectorize fine…
was stil not ok in gcc version 4.7.0 20110702 (experimental) (GCC) 


it still pretends to check for
test/vectClass.cpp:11: note: Detected interleaving this_9(D)->a and this_9(D)->b
test/vectClass.cpp:11: note: versioning for alias required: can't determine dependence between this_9(D)->a and *D.1537_8
test/vectClass.cpp:11: note: mark for run-time aliasing test between this_9(D)->a and *D.1537_8
test/vectClass.cpp:11: note: versioning for alias required: can't determine dependence between this_9(D)->b and *D.1537_8
test/vectClass.cpp:11: note: mark for run-time aliasing test between this_9(D)->b and *D.1537_8

I hope it will be addressed in PR49774