[Bug fortran/83650] [6/7/8 Regression] Wrong simplification in cshift with negative shifts

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83650

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|7.4                         |6.5

--- Comment #2 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Patch for gcc-7:

Index: fortran/simplify.c
===================================================================
--- fortran/simplify.c  (Revision 256009)
+++ fortran/simplify.c  (Arbeitskopie)
@@ -1991,7 +1991,9 @@ gfc_simplify_cshift (gfc_expr *array, gfc_expr *sh
       mpz_clear (size);

       /* Adjust shft to deal with right or left shifts. */
-      shft = shft < 0 ? 1 - shft : shft;
+      shft = shft % sz;
+      if (shft < 0)
+       shft += sz;

       /* Special case: Shift to the original order!  */
       if (sz == 0 || shft % sz == 0)
Index: testsuite/gfortran.dg/simplify_cshift_1.f90
===================================================================
--- testsuite/gfortran.dg/simplify_cshift_1.f90 (Revision 256009)
+++ testsuite/gfortran.dg/simplify_cshift_1.f90 (Arbeitskopie)
@@ -23,12 +23,12 @@ program foo
    v = cshift(c, 2)
    if (any(b /= v)) call abort

-   ! Special cases shift = 0, size(a), 1-size(a)
+   ! Special cases shift = 0, size(a), size(a)
    b = cshift([1, 2, 3, 4, 5], 0)
    if (any(b /= a)) call abort
    b = cshift([1, 2, 3, 4, 5], size(a))
    if (any(b /= a)) call abort
-   b = cshift([1, 2, 3, 4, 5], 1-size(a))
+   b = cshift([1, 2, 3, 4, 5], -size(a))
    if (any(b /= a)) call abort

    ! simplification of array arg.