Re: Polyhedron test: gas_dyn run-time performance regression compared with yesterday

["Uros Bizjak" <ubizjak at gmail dot com>]

Hello!

> This is using the Polyhedron Fortran test.
> http://www.polyhedron.co.uk/MFL6VW74649

> Using several options, the gas_dyn test got much slower; however, with
> some options, the performance remained roughly the same.
> In terms of the geometric mean, it is a slowdown of around 1%.
> The run time of the other programs only changed slightly (up/down/const).


> Result from http://www.suse.de/~gcctest/c++bench/polyhedron/
> -ffast-math -funroll-loops -O3 -ftree-vectorize -march= ??? (opteron I
> think).
> 14.59s -> 21.06s (44% slower)


> Result on for my AMD Athlon64 4800+,
> http://physik.fu-berlin.de/~tburnus/gcc-trunk/benchmark/
> Yesterday: 2007-09-10-r128322
> Today: 2007-09-11-r128363

The problem was introduced by r128353 [1]:

2007-09-10  Harsha Jagasia <harsha.jagasia@amd.com>
            Jan Sjodin <jan.sjodin@amd.com>

        * tree-vect-analyze.c (vect_analyze_operations): Change
        comparison of loop iterations with threshold to less than
        or equal to instead of less than. Reduce
        min_scalar_loop_bound by one.
        * tree-vect-transform.c (vect_estimate_min_profitable_iters):
        Change prologue and epilogue iterations estimate to vf/2,
        when unknown at compile-time. Change versioning guard
        cost to taken_branch_cost. If peeling for alignment is
        unknown at compile-time, change peel guard costs to one
        taken branch and one not-taken branch per peeled loop.
        If peeling for alignment is known but number of scalar loop
        iterations is unknown at compile-time, change peel guard
        costs to one taken branch per peeled loop. Change the cost
        model equation to consider vector iterations as the loop
        iterations less the prologue and epilogue iterations.
        Change outside vector cost check to less than or equal to
        zero instead of equal to zero.
        (vect_do_peeling_for_loop_bound): Reduce
        min_scalar_loop_bound by one.
        * tree-vectorizer.h: Add TARG_COND_TAKEN_BRANCH_COST and
        TARG_COND_NOT_TAKEN_BRANCH_COST.
        ...

[1]: http://gcc.gnu.org/ml/gcc-cvs/2007-09/msg00347.html

Uros.