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[Bug tree-optimization/79744] New: [7 Regression] The polyhedron test rnflow.f90 is miscompiled with -O3 after r236361


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79744

            Bug ID: 79744
           Summary: [7 Regression] The polyhedron test rnflow.f90 is
                    miscompiled with -O3 after r236361
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dominiq at lps dot ens.fr
                CC: rguenth at gcc dot gnu.org
  Target Milestone: ---

When compiled with gfortran 6.3.0 (or trunk up to r236319) and -O3, the
polyhedron test rnflow.f90 gives the output

...
         173 ,         181        194373      193363  0.519999981    
         173 ,         189         78369       78008  0.460000008    
         173 ,         197         19089       18777   1.63000000    
         181 ,         189         81645       81532  0.140000001    
         181 ,         197         29924       29571   1.17999995    
         189 ,         197         32866       33059  0.579999983    
         189 ,         205         12258       12352  0.759999990    
         197 ,         205         10923       10786   1.25000000    
         205 ,         213          3278        3208   2.14000010    
  0: 0:17.492 -> Completed program execution

After revision r236361 (pr71168)

...
         165 ,         197          9830        9748  0.829999983    
         165 ,         205          1529        1461   4.44999981    
         173 ,         181        194373      194038  0.170000002    
         173 ,         189         78369       78584  0.270000011    
         173 ,         197         19089       19180  0.469999999    
         181 ,         189         81645       81303  0.419999987    
         181 ,         197         29924       30302   1.25000000    
         189 ,         205         12258       12546   2.29999995    
         197 ,         213          2790        2698   3.29999995    
  0: 0:22.058 -> Completed program execution

Note also that the execution time increases by ~30%.

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