[gfortran] Patch for optimized Arithmetic IF

[Canqun Yang]

Hi, all,

In case of equal labels, ARITHMETIC IF can be translated to a simple version.

E.g.
   IF (a) 10, 20, 20
   
   can be translated to
   
   if (a < 0) goto label_10;
   else goto label_20; 
  
   instead of the current one generated by GCC Fortran 95 frontend.

    if (a <= 0)
      {
        if (a < 0) goto label_10;
        else goto label_20;
      }
    else
      goto label_20;

This patch can lead the previous optimized code, OK to apply?

Canqun Yang
Creative Compiler Research Group.
National University of Defense Technology, China.
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