[Bug tree-optimization/45216] Rotate expressions not recognized at tree level

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45216



--- Comment #8 from Marc Glisse <glisse at gcc dot gnu.org> 2012-12-01 08:51:12 
UTC ---

(In reply to comment #7)

> unsigned long rotate_left(unsigned long a, unsigned int shift)

> {

>         return a << shift | a >> (sizeof(a) * 8 - shift);

> }



We have a regression in C++ in 4.8 there. Comparing -O3 -fdump-tree-optimized

in gcc-4.7, g++-4.7 and gcc-4.8:



  D.1708_3 = a_1(D) r<< shift_2(D);



and in g++-4.8:



  shift.0_2 = (int) shift_1(D);

  _4 = a_3(D) << shift.0_2;

  _5 = 64 - shift_1(D);

  _6 = (int) _5;

  _7 = a_3(D) >> _6;

  _8 = _7 | _4;