[Bug tree-optimization/89713] Optimize away an empty loop whose finiteness can not be analytically determined

[fxue at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89713

--- Comment #5 from fxue at gcc dot gnu.org ---
Author: fxue
Date: Thu Jun 13 04:17:42 2019
New Revision: 272234

URL: https://gcc.gnu.org/viewcvs?rev=272234&root=gcc&view=rev
Log:
PR tree-optimization/89713 - Assume loop with an exit is finite

gcc/ChangeLog:

        * doc/invoke.texi (-ffinite-loops): Document new option.
        * common.opt (-ffinite-loops): New option.
        * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Mark
        IFN_GOACC_LOOP calls as necessary.
        * tree-ssa-loop-niter.c (finite_loop_p): Assume loop with an exit
        is finite.
        * omp-offload.c (oacc_xform_loop): Skip lowering if return value of
        IFN_GOACC_LOOP call is not used.
        * opts.c (default_options_table): Enable -ffinite-loops at -O2+.

gcc/testsuite/ChangeLog:

        * g++.dg/tree-ssa/empty-loop.C: New test.
        * gcc.dg/tree-ssa/dce-2.c: New test.
        * gcc.dg/const-1.c: Add -fno-finite-loops option.
        * gcc.dg/graphite/graphite.exp: Likewise.
        * gcc.dg/loop-unswitch-1.c: Likewise.
        * gcc.dg/predict-9.c: Likewise.
        * gcc.dg/pure-2.c: Likewise.
        * gcc.dg/tree-ssa/20040211-1.c: Likewise.
        * gcc.dg/tree-ssa/loop-10.c: Likewise.
        * gcc.dg/tree-ssa/split-path-6.c: Likewise.
        * gcc.dg/tree-ssa/ssa-thread-12.c: Likewise.

libgomp/ChangeLog:

        * testsuite/libgomp.oacc-c-c++-common/pr84955-1.c: New test.

Added:
    trunk/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
    trunk/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c
    trunk/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/common.opt
    trunk/gcc/doc/invoke.texi
    trunk/gcc/omp-offload.c
    trunk/gcc/opts.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/const-1.c
    trunk/gcc/testsuite/gcc.dg/graphite/graphite.exp
    trunk/gcc/testsuite/gcc.dg/loop-unswitch-1.c
    trunk/gcc/testsuite/gcc.dg/predict-9.c
    trunk/gcc/testsuite/gcc.dg/pure-2.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c
    trunk/gcc/tree-ssa-dce.c
    trunk/gcc/tree-ssa-loop-niter.c
    trunk/libgomp/ChangeLog