Hi Thomas!
Am 21.06.26 um 4:46 PM schrieb Thomas Koenig:
Hello world,
what it says in the ChangeLog entry. Regression-tested (and the test
case makes sure there is no wrong-code regression).
OK for trunk?
Best regards
Thomas
Rewrite (-1.0)**n to (real) (1 - (n & 1) << 1)).
The problem was that the optimization done for PR 57073 uses powi and
friends, so it only applied to default integer exponent. The test
case has an integer(kind=8) exponent, which is is calculated by
calling a gfortran library function.
There are two possible approaches: One would be to convert all
integer types to default integer (because only the lowest-value
bit matters to the result) and call the right __builtin_powi function.
However, the generated code is suboptimal, see PR 125919. I therefore
chose the variant which currently generates the best code.
This is OK.
This requires the change to the power_6.f90 test case.
I am somewhat confused by the dg-pattern here. It is
! { dg-final { scan-tree-dump-not "__builtin_powif" "optimized" } }
In principle you do not want to see the __builtin_powif in the
original dump. If someone chose to add an optimization that expands
the __builtin_powif to something else, you do not realize it.
(This is not your fault, though.)
I find your testcase power_10.f90 quite interesting. It rather tests
floating-point arithmetic and may fail at different optimization levels
because of tests like
+ if (s4 /= 2.30965209) stop 11
(plus several more).
Please convince yourself and also test with other compilers.
Either add a suitable tolerance, or just test what needs to be
tested.
(One option: one can compare compile-time with run-time results,
which possibly makes it easier to trace testsuite fallout.)
Maybe use something like
real, parameter :: expected(*) = [((-1.0)**i,i=-10,10)]
etc.
The patch is OK with the above suitably considered.
Thanks,
Harald
gcc/fortran/ChangeLog:
PR fortran/125914
* trans-expr.cc (gfc_conv_power_op): Rewrite (-1.0)**n into
(real) (1 - (n & 1) << 1)).
gcc/testsuite/ChangeLog:
PR fortran/125914
* gfortran.dg/power_6.f90: Remove scans for powi.
* gfortran.dg/power_10.f90: New test.
