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.

From-SVN: r272234

1 files changed, 11 insertions, 0 deletions

diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 2478219..a38899e 100644
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -245,6 +245,17 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool aggressive)
 	    mark_stmt_necessary (stmt, true);
 	    return;
 	  }
+	/* IFN_GOACC_LOOP calls are necessary in that they are used to
+	   represent parameter (i.e. step, bound) of a lowered OpenACC
+	   partitioned loop.  But this kind of partitioned loop might not
+	   survive from aggressive loop removal for it has loop exit and
+	   is assumed to be finite.  Therefore, we need to explicitly mark
+	   these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
+	if (gimple_call_internal_p (stmt, IFN_GOACC_LOOP))
+	  {
+	    mark_stmt_necessary (stmt, true);
+	    return;
+	  }
 	if (!gimple_call_lhs (stmt))
 	  return;
 	break;