Fortran: fix FAIL of gfortran.dg/specifics_1.f90 after r16-372 [PR120099]

After commit r16-372, testcase gfortran.dg/specifics_1.f90 started to
FAIL at -O2 and higher, as DCE lead to elimination of evaluations of
Fortran specific intrinsics returning complex results and with -ff2c.
As the Fortran runtime library is compiled with -fno-f2c, the frontend
generates calls to wrapper subroutines _gfortran_f2c_specific_* that
return their result by reference via their first argument when this is
needed.  This is e.g. the case when specific names of the intrinsics are
used for passing as actual argument to procedures.  These wrappers are
not pure in the GCC IR sense, even if the Fortran intrinsics are.
Therefore gfc_return_by_reference must return true for these.

	PR fortran/120099

gcc/fortran/ChangeLog:

	* trans-types.cc (gfc_return_by_reference): Intrinsic functions
	returning complex numbers may return their result by reference
	with -ff2c.

diff --git a/gcc/fortran/trans-types.cc b/gcc/fortran/trans-types.cc
index f898075468568648280a3927f5a71a1d762cb726..e15b1bb89f01ff88fb679f5dbd4667fdd00990d9 100644 (file)
--- a/gcc/fortran/trans-types.cc
+++ b/gcc/fortran/trans-types.cc
@@ -3231,13 +3231,14 @@ gfc_return_by_reference (gfc_symbol * sym)
 
   /* Possibly return complex numbers by reference for g77 compatibility.
      We don't do this for calls to intrinsics (as the library uses the
-     -fno-f2c calling convention), nor for calls to functions which always
+     -fno-f2c calling convention) except for calls to specific wrappers
+     (_gfortran_f2c_specific_*), nor for calls to functions which always
      require an explicit interface, as no compatibility problems can
      arise there.  */
   if (flag_f2c && sym->ts.type == BT_COMPLEX
       && !sym->attr.pointer
       && !sym->attr.allocatable
-      && !sym->attr.intrinsic && !sym->attr.always_explicit)
+      && !sym->attr.always_explicit)
     return 1;
 
   return 0;