[Bug middle-end/49959] New: ABS pattern is not recognized

[enkovich.gnu at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49959

           Summary: ABS pattern is not recognized
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: enkovich....@gmail.com


Created attachment 24900
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24900
Simple test where ABS pattern is not recognized

Here is optimization opportunity for ABS pattern recognizer which does not
catch all cases.

Here is a simple test for ABS computation:

#define ABS(X)    (((X)>0)?(X):-(X))
int
test_abs(int *cur)
{
  unsigned long sad = 0;
  sad = ABS(cur[0]);
  return sad;
}

GIMPLE for the test is good (phase optimized):

test_abs (int * cur)
{
  int D.2783;
  int D.2782;

<bb 2>:
  D.2782_3 = *cur_2(D);
  D.2783_4 = ABS_EXPR <D.2782_3>;
  return D.2783_4;
}

Now try to make a minor change in test:
#define ABS(X)    (((X)>0)?(X):-(X))
int
test_abs(int *cur)
{
  unsigned long sad = 0;
  sad += ABS(cur[0]);
  return sad;
}

GIMPLE becomes worse:

test_abs (int * cur)
{
  int D.2788;
  int D.2787;
  int D.2783;
  long unsigned int iftmp.0;

<bb 2>:
  D.2783_4 = *cur_3(D);
  if (D.2783_4 > 0)
    goto <bb 3>;
  else
    goto <bb 4>;

<bb 3>:
  iftmp.0_6 = (long unsigned int) D.2783_4;
  goto <bb 5>;

<bb 4>:
  D.2787_8 = -D.2783_4;
  iftmp.0_9 = (long unsigned int) D.2787_8;

<bb 5>:
  # iftmp.0_1 = PHI <iftmp.0_6(3), iftmp.0_9(4)>
  D.2788_11 = (int) iftmp.0_1;
  return D.2788_11;
}

Compiler used for tests:

Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure --prefix=/export/gcc-build
--enable-languages=c,c++,fortran
Thread model: posix
gcc version 4.7.0 20110707 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-S' '-mtune=generic'
'-march=x86-64'