[V8] Remove empty loop with assumed finiteness (PR tree-optimization/89713)

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  • [V8] Remove empty loop with assumed finiteness (PR tree-optimization/89713)
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Commit Message

Feng Xue OS June 11, 2019, 2:40 a.m.
Reformat to comply with gcc coding style.

Feng

---
-- 
1.8.3.1

Comments

Richard Biener June 12, 2019, 9:42 a.m. | #1
On Tue, Jun 11, 2019 at 4:40 AM Feng Xue OS <fxue@os.amperecomputing.com> wrote:
>

> Reformat to comply with gcc coding style.


OK for trunk.

Thanks,
Richard.

> Feng

>

> ---

> diff --git a/gcc/ChangeLog b/gcc/ChangeLog

> index 37aab79..87cc125 100644

> --- a/gcc/ChangeLog

> +++ b/gcc/ChangeLog

> @@ -1,3 +1,16 @@

> +2019-06-04  Feng Xue  <fxue@os.amperecomputing.com>

> +

> +       PR tree-optimization/89713

> +       * 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+.

> +

>  2019-06-04  Alan Modra  <amodra@gmail.com>

>

>         PR target/90689

> diff --git a/gcc/common.opt b/gcc/common.opt

> index 0e72fd0..8b0e6ad 100644

> --- a/gcc/common.opt

> +++ b/gcc/common.opt

> @@ -1437,6 +1437,10 @@ ffinite-math-only

>  Common Report Var(flag_finite_math_only) Optimization SetByCombined

>  Assume no NaNs or infinities are generated.

>

> +ffinite-loops

> +Common Report Var(flag_finite_loops) Optimization

> +Assume that loops with an exit will terminate and not loop indefinitely.

> +

>  ffixed-

>  Common Joined RejectNegative Var(common_deferred_options) Defer

>  -ffixed-<register>     Mark <register> as being unavailable to the compiler.

> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi

> index 91c9bb8..1e12595 100644

> --- a/gcc/doc/invoke.texi

> +++ b/gcc/doc/invoke.texi

> @@ -412,6 +412,7 @@ Objective-C and Objective-C++ Dialects}.

>  -fdevirtualize-at-ltrans  -fdse @gol

>  -fearly-inlining  -fipa-sra  -fexpensive-optimizations  -ffat-lto-objects @gol

>  -ffast-math  -ffinite-math-only  -ffloat-store  -fexcess-precision=@var{style} @gol

> +-ffinite-loops @gol

>  -fforward-propagate  -ffp-contract=@var{style}  -ffunction-sections @gol

>  -fgcse  -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity @gol

>  -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion @gol

> @@ -8282,6 +8283,7 @@ also turns on the following optimization flags:

>  -fdelete-null-pointer-checks @gol

>  -fdevirtualize  -fdevirtualize-speculatively @gol

>  -fexpensive-optimizations @gol

> +-ffinite-loops @gol

>  -fgcse  -fgcse-lm  @gol

>  -fhoist-adjacent-loads @gol

>  -finline-small-functions @gol

> @@ -9503,6 +9505,15 @@ that may set @code{errno} but are otherwise free of side effects.  This flag is

>  enabled by default at @option{-O2} and higher if @option{-Os} is not also

>  specified.

>

> +@item -ffinite-loops

> +@opindex ffinite-loops

> +@opindex fno-finite-loops

> +Assume that a loop with an exit will eventually take the exit and not loop

> +indefinitely.  This allows the compiler to remove loops that otherwise have

> +no side-effects, not considering eventual endless looping as such.

> +

> +This option is enabled by default at @option{-O2}.

> +

>  @item -ftree-dominator-opts

>  @opindex ftree-dominator-opts

>  Perform a variety of simple scalar cleanups (constant/copy

> diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c

> index 97ae47b..c8a281c 100644

> --- a/gcc/omp-offload.c

> +++ b/gcc/omp-offload.c

> @@ -300,7 +300,7 @@ oacc_xform_loop (gcall *call)

>    tree chunk_size = NULL_TREE;

>    unsigned mask = (unsigned) TREE_INT_CST_LOW (gimple_call_arg (call, 5));

>    tree lhs = gimple_call_lhs (call);

> -  tree type = TREE_TYPE (lhs);

> +  tree type = NULL_TREE;

>    tree diff_type = TREE_TYPE (range);

>    tree r = NULL_TREE;

>    gimple_seq seq = NULL;

> @@ -308,6 +308,15 @@ oacc_xform_loop (gcall *call)

>    unsigned outer_mask = mask & (~mask + 1); // Outermost partitioning

>    unsigned inner_mask = mask & ~outer_mask; // Inner partitioning (if any)

>

> +  /* Skip lowering if return value of IFN_GOACC_LOOP call is not used.  */

> +  if (!lhs)

> +    {

> +      gsi_replace_with_seq (&gsi, seq, true);

> +      return;

> +    }

> +

> +  type = TREE_TYPE (lhs);

> +

>  #ifdef ACCEL_COMPILER

>    chunk_size = gimple_call_arg (call, 4);

>    if (integer_minus_onep (chunk_size)  /* Force static allocation.  */

> diff --git a/gcc/opts.c b/gcc/opts.c

> index 64f94ac..b38bfb1 100644

> --- a/gcc/opts.c

> +++ b/gcc/opts.c

> @@ -494,6 +494,7 @@ static const struct default_options default_options_table[] =

>      { OPT_LEVELS_2_PLUS, OPT_fdevirtualize, NULL, 1 },

>      { OPT_LEVELS_2_PLUS, OPT_fdevirtualize_speculatively, NULL, 1 },

>      { OPT_LEVELS_2_PLUS, OPT_fexpensive_optimizations, NULL, 1 },

> +    { OPT_LEVELS_2_PLUS, OPT_ffinite_loops, NULL, 1 },

>      { OPT_LEVELS_2_PLUS, OPT_fgcse, NULL, 1 },

>      { OPT_LEVELS_2_PLUS, OPT_fhoist_adjacent_loads, NULL, 1 },

>      { OPT_LEVELS_2_PLUS, OPT_findirect_inlining, NULL, 1 },

> diff --git a/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C

> new file mode 100644

> index 0000000..6b1e879

> --- /dev/null

> +++ b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C

> @@ -0,0 +1,33 @@

> +/* { dg-do compile } */

> +/* { dg-options "-O2 -fdump-tree-cddce2 -ffinite-loops" } */

> +

> +#include <string>

> +#include <vector>

> +#include <list>

> +#include <set>

> +#include <map>

> +

> +using namespace std;

> +

> +int foo (vector<string> &v, list<string> &l, set<string> &s, map<int, string> &m)

> +{

> +  for (vector<string>::iterator it = v.begin (); it != v.end (); ++it)

> +    it->length();

> +

> +  for (list<string>::iterator it = l.begin (); it != l.end (); ++it)

> +    it->length();

> +

> +  for (map<int, string>::iterator it = m.begin (); it != m.end (); ++it)

> +    it->first + it->second.length();

> +

> +  for (set<string>::iterator it0 = s.begin (); it0 != s.end(); ++it0)

> +    for (vector<string>::reverse_iterator it1 = v.rbegin(); it1 != v.rend(); ++it1)

> +      {

> +        it0->length();

> +        it1->length();

> +      }

> +

> +  return 0;

> +}

> +/* { dg-final { scan-tree-dump-not "if" "cddce2"} } */

> +

> diff --git a/gcc/testsuite/gcc.dg/const-1.c b/gcc/testsuite/gcc.dg/const-1.c

> index a5b2b16..2e95bd8 100644

> --- a/gcc/testsuite/gcc.dg/const-1.c

> +++ b/gcc/testsuite/gcc.dg/const-1.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile { target nonpic } } */

> -/* { dg-options "-O2 -Wsuggest-attribute=const" } */

> +/* { dg-options "-O2 -Wsuggest-attribute=const -fno-finite-loops" } */

>

>  extern int extern_const(int a) __attribute__ ((const));

>

> diff --git a/gcc/testsuite/gcc.dg/graphite/graphite.exp b/gcc/testsuite/gcc.dg/graphite/graphite.exp

> index ea61446..523a955 100644

> --- a/gcc/testsuite/gcc.dg/graphite/graphite.exp

> +++ b/gcc/testsuite/gcc.dg/graphite/graphite.exp

> @@ -56,7 +56,7 @@ set vect_files        [lsort [glob -nocomplain $srcdir/$subdir/vect-*.c ] ]

>

>  # Tests to be compiled.

>  set dg-do-what-default compile

> -dg-runtest $scop_files        "" "-O2 -fgraphite -fdump-tree-graphite-all"

> +dg-runtest $scop_files        "" "-O2 -fgraphite -fdump-tree-graphite-all -fno-finite-loops"

>  dg-runtest $id_files          "" "-O2 -fgraphite-identity -ffast-math -fdump-tree-graphite-details"

>

>  # Tests to be run.

> diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-1.c b/gcc/testsuite/gcc.dg/loop-unswitch-1.c

> index f6fc41d..de2fb2c 100644

> --- a/gcc/testsuite/gcc.dg/loop-unswitch-1.c

> +++ b/gcc/testsuite/gcc.dg/loop-unswitch-1.c

> @@ -1,6 +1,6 @@

>  /* For PR rtl-optimization/27735  */

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details" } */

> +/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details -fno-finite-loops" } */

>

>  void set_color(void);

>  void xml_colorize_line(unsigned int *p, int state)

> diff --git a/gcc/testsuite/gcc.dg/predict-9.c b/gcc/testsuite/gcc.dg/predict-9.c

> index 7e5ba08..f491c51 100644

> --- a/gcc/testsuite/gcc.dg/predict-9.c

> +++ b/gcc/testsuite/gcc.dg/predict-9.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-profile_estimate" } */

> +/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-profile_estimate -fno-finite-loops" } */

>

>  extern int global;

>  extern int global2;

> diff --git a/gcc/testsuite/gcc.dg/pure-2.c b/gcc/testsuite/gcc.dg/pure-2.c

> index fe6e2bc..318cfd1 100644

> --- a/gcc/testsuite/gcc.dg/pure-2.c

> +++ b/gcc/testsuite/gcc.dg/pure-2.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -Wsuggest-attribute=pure" } */

> +/* { dg-options "-O2 -Wsuggest-attribute=pure -fno-finite-loops" } */

>  /* { dg-add-options bind_pic_locally } */

>

>  extern int extern_const(int a) __attribute__ ((pure));

> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c b/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c

> index d289e5d..a9bdf26 100644

> --- a/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c

> +++ b/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -fdump-tree-cddce2" } */

> +/* { dg-options "-O2 -fdump-tree-cddce2 -fno-finite-loops" } */

>

>  struct rtx_def;

>  typedef struct rtx_def *rtx;

> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c b/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c

> new file mode 100644

> index 0000000..18c1ddb

> --- /dev/null

> +++ b/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c

> @@ -0,0 +1,37 @@

> +/* { dg-do compile } */

> +/* { dg-options "-O2 -fdump-tree-cddce1 -ffinite-loops" } */

> +

> +typedef struct list {

> +    char pad[15];

> +    struct list *next;

> +} list;

> +

> +int data;

> +

> +list *head, *tail;

> +

> +int __attribute__((pure)) pfn (int);

> +

> +int foo (unsigned u, int s)

> +{

> +  unsigned i;

> +  list *p;

> +  int j;

> +

> +  for (i = 0; i < u; i += 2)

> +    ;

> +

> +  for (p = head; p; p = p->next)

> +    ;

> +

> +  for (j = data; j & s; j = pfn (j + 3))

> +    ;

> +

> +  for (p = head; p != tail; p = p->next)

> +    for (j = data + 1; j > s; j = pfn (j + 2))

> +      ;

> +

> +  return 0;

> +}

> +/* { dg-final { scan-tree-dump-not "if" "cddce1"} } */

> +

> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c b/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c

> index a29c9fb..3d05ad2 100644

> --- a/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c

> +++ b/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -fdump-tree-optimized" } */

> +/* { dg-options "-O2 -fdump-tree-optimized -fno-finite-loops" } */

>  /* { dg-require-effective-target int32plus } */

>

>  int bar (void);

> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c b/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c

> index e9b4f26..187c084 100644

> --- a/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c

> +++ b/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -fsplit-paths -fno-tree-cselim -fdump-tree-split-paths-details -w" } */

> +/* { dg-options "-O2 -fsplit-paths -fno-tree-cselim -fdump-tree-split-paths-details -w -fno-finite-loops" } */

>

>  struct __sFILE

>  {

> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c

> index d829b04..6752676 100644

> --- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c

> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c

> @@ -1,5 +1,5 @@

>  /* { dg-do compile } */

> -/* { dg-options "-O2 -fdump-tree-thread2-details -fdump-tree-thread3-details -fdump-tree-thread4-details" } */

> +/* { dg-options "-O2 -fdump-tree-thread2-details -fdump-tree-thread3-details -fdump-tree-thread4-details -fno-finite-loops" } */

>  /* { dg-final { scan-tree-dump "FSM" "thread2" } } */

>  /* { dg-final { scan-tree-dump "FSM" "thread3" } } */

>  /* { dg-final { scan-tree-dump "FSM" "thread4" { xfail *-*-* } } } */

> 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;

> diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c

> index 470b6a2..9b9cb41 100644

> --- a/gcc/tree-ssa-loop-niter.c

> +++ b/gcc/tree-ssa-loop-niter.c

> @@ -2798,6 +2798,27 @@ finite_loop_p (struct loop *loop)

>                  loop->num);

>        return true;

>      }

> +

> +  if (flag_finite_loops)

> +    {

> +      unsigned i;

> +      vec<edge> exits = get_loop_exit_edges (loop);

> +      edge ex;

> +

> +      /* If the loop has a normal exit, we can assume it will terminate.  */

> +      FOR_EACH_VEC_ELT (exits, i, ex)

> +       if (!(ex->flags & (EDGE_EH | EDGE_ABNORMAL | EDGE_FAKE)))

> +         {

> +           exits.release ();

> +           if (dump_file)

> +             fprintf (dump_file, "Assume loop %i to be finite: it has an exit "

> +                      "and -ffinite-loops is on.\n", loop->num);

> +           return true;

> +         }

> +

> +      exits.release ();

> +    }

> +

>    return false;

>  }

>

> diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c

> new file mode 100644

> index 0000000..44767cd

> --- /dev/null

> +++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c

> @@ -0,0 +1,31 @@

> +/* { dg-do compile }  */

> +/* { dg-options "-O2 -fdump-tree-cddce2 -ffinite-loops" } */

> +

> +int

> +f1 (void)

> +{

> +  int i, j;

> +

> +#pragma acc parallel loop tile(2,3)

> +  for (i = 1; i < 10; i++)

> +    for (j = 1; j < 10; j++)

> +      for (;;)

> +       ;

> +

> +  return i + j;

> +}

> +

> +int

> +f2 (void)

> +{

> +  int i, j, k;

> +

> +#pragma acc parallel loop tile(2,3)

> +  for (i = 1; i < 10; i++)

> +    for (j = 1; j < 10; j++)

> +      for (k = 1; k < 10; k++)

> +       ;

> +

> +  return i + j;

> +}

> +/* { dg-final { scan-tree-dump-not "if" "cddce2"} } */

> --

> 1.8.3.1

Patch

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 37aab79..87cc125 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,16 @@ 
+2019-06-04  Feng Xue  <fxue@os.amperecomputing.com>
+
+	PR tree-optimization/89713
+	* 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+.
+
 2019-06-04  Alan Modra  <amodra@gmail.com>
 
 	PR target/90689
diff --git a/gcc/common.opt b/gcc/common.opt
index 0e72fd0..8b0e6ad 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1437,6 +1437,10 @@  ffinite-math-only
 Common Report Var(flag_finite_math_only) Optimization SetByCombined
 Assume no NaNs or infinities are generated.
 
+ffinite-loops
+Common Report Var(flag_finite_loops) Optimization
+Assume that loops with an exit will terminate and not loop indefinitely.
+
 ffixed-
 Common Joined RejectNegative Var(common_deferred_options) Defer
 -ffixed-<register>	Mark <register> as being unavailable to the compiler.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 91c9bb8..1e12595 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -412,6 +412,7 @@  Objective-C and Objective-C++ Dialects}.
 -fdevirtualize-at-ltrans  -fdse @gol
 -fearly-inlining  -fipa-sra  -fexpensive-optimizations  -ffat-lto-objects @gol
 -ffast-math  -ffinite-math-only  -ffloat-store  -fexcess-precision=@var{style} @gol
+-ffinite-loops @gol
 -fforward-propagate  -ffp-contract=@var{style}  -ffunction-sections @gol
 -fgcse  -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity @gol
 -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion @gol
@@ -8282,6 +8283,7 @@  also turns on the following optimization flags:
 -fdelete-null-pointer-checks @gol
 -fdevirtualize  -fdevirtualize-speculatively @gol
 -fexpensive-optimizations @gol
+-ffinite-loops @gol
 -fgcse  -fgcse-lm  @gol
 -fhoist-adjacent-loads @gol
 -finline-small-functions @gol
@@ -9503,6 +9505,15 @@  that may set @code{errno} but are otherwise free of side effects.  This flag is
 enabled by default at @option{-O2} and higher if @option{-Os} is not also
 specified.
 
+@item -ffinite-loops
+@opindex ffinite-loops
+@opindex fno-finite-loops
+Assume that a loop with an exit will eventually take the exit and not loop
+indefinitely.  This allows the compiler to remove loops that otherwise have
+no side-effects, not considering eventual endless looping as such.
+
+This option is enabled by default at @option{-O2}.
+
 @item -ftree-dominator-opts
 @opindex ftree-dominator-opts
 Perform a variety of simple scalar cleanups (constant/copy
diff --git a/gcc/omp-offload.c b/gcc/omp-offload.c
index 97ae47b..c8a281c 100644
--- a/gcc/omp-offload.c
+++ b/gcc/omp-offload.c
@@ -300,7 +300,7 @@  oacc_xform_loop (gcall *call)
   tree chunk_size = NULL_TREE;
   unsigned mask = (unsigned) TREE_INT_CST_LOW (gimple_call_arg (call, 5));
   tree lhs = gimple_call_lhs (call);
-  tree type = TREE_TYPE (lhs);
+  tree type = NULL_TREE;
   tree diff_type = TREE_TYPE (range);
   tree r = NULL_TREE;
   gimple_seq seq = NULL;
@@ -308,6 +308,15 @@  oacc_xform_loop (gcall *call)
   unsigned outer_mask = mask & (~mask + 1); // Outermost partitioning
   unsigned inner_mask = mask & ~outer_mask; // Inner partitioning (if any)
 
+  /* Skip lowering if return value of IFN_GOACC_LOOP call is not used.  */
+  if (!lhs)
+    {
+      gsi_replace_with_seq (&gsi, seq, true);
+      return;
+    }
+
+  type = TREE_TYPE (lhs);
+
 #ifdef ACCEL_COMPILER
   chunk_size = gimple_call_arg (call, 4);
   if (integer_minus_onep (chunk_size)  /* Force static allocation.  */
diff --git a/gcc/opts.c b/gcc/opts.c
index 64f94ac..b38bfb1 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -494,6 +494,7 @@  static const struct default_options default_options_table[] =
     { OPT_LEVELS_2_PLUS, OPT_fdevirtualize, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_fdevirtualize_speculatively, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_fexpensive_optimizations, NULL, 1 },
+    { OPT_LEVELS_2_PLUS, OPT_ffinite_loops, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_fgcse, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_fhoist_adjacent_loads, NULL, 1 },
     { OPT_LEVELS_2_PLUS, OPT_findirect_inlining, NULL, 1 },
diff --git a/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
new file mode 100644
index 0000000..6b1e879
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/empty-loop.C
@@ -0,0 +1,33 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce2 -ffinite-loops" } */
+
+#include <string>
+#include <vector>
+#include <list>
+#include <set>
+#include <map>
+
+using namespace std;
+
+int foo (vector<string> &v, list<string> &l, set<string> &s, map<int, string> &m)
+{
+  for (vector<string>::iterator it = v.begin (); it != v.end (); ++it)
+    it->length();
+
+  for (list<string>::iterator it = l.begin (); it != l.end (); ++it)
+    it->length();
+
+  for (map<int, string>::iterator it = m.begin (); it != m.end (); ++it)
+    it->first + it->second.length();
+
+  for (set<string>::iterator it0 = s.begin (); it0 != s.end(); ++it0)
+    for (vector<string>::reverse_iterator it1 = v.rbegin(); it1 != v.rend(); ++it1)
+      {
+        it0->length();
+        it1->length();
+      }  
+
+  return 0;
+}
+/* { dg-final { scan-tree-dump-not "if" "cddce2"} } */
+
diff --git a/gcc/testsuite/gcc.dg/const-1.c b/gcc/testsuite/gcc.dg/const-1.c
index a5b2b16..2e95bd8 100644
--- a/gcc/testsuite/gcc.dg/const-1.c
+++ b/gcc/testsuite/gcc.dg/const-1.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile { target nonpic } } */
-/* { dg-options "-O2 -Wsuggest-attribute=const" } */
+/* { dg-options "-O2 -Wsuggest-attribute=const -fno-finite-loops" } */
 
 extern int extern_const(int a) __attribute__ ((const));
 
diff --git a/gcc/testsuite/gcc.dg/graphite/graphite.exp b/gcc/testsuite/gcc.dg/graphite/graphite.exp
index ea61446..523a955 100644
--- a/gcc/testsuite/gcc.dg/graphite/graphite.exp
+++ b/gcc/testsuite/gcc.dg/graphite/graphite.exp
@@ -56,7 +56,7 @@  set vect_files        [lsort [glob -nocomplain $srcdir/$subdir/vect-*.c ] ]
 
 # Tests to be compiled.
 set dg-do-what-default compile
-dg-runtest $scop_files        "" "-O2 -fgraphite -fdump-tree-graphite-all"
+dg-runtest $scop_files        "" "-O2 -fgraphite -fdump-tree-graphite-all -fno-finite-loops"
 dg-runtest $id_files          "" "-O2 -fgraphite-identity -ffast-math -fdump-tree-graphite-details"
 
 # Tests to be run.
diff --git a/gcc/testsuite/gcc.dg/loop-unswitch-1.c b/gcc/testsuite/gcc.dg/loop-unswitch-1.c
index f6fc41d..de2fb2c 100644
--- a/gcc/testsuite/gcc.dg/loop-unswitch-1.c
+++ b/gcc/testsuite/gcc.dg/loop-unswitch-1.c
@@ -1,6 +1,6 @@ 
 /* For PR rtl-optimization/27735  */
 /* { dg-do compile } */
-/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details" } */
+/* { dg-options "-O2 -funswitch-loops -fdump-tree-unswitch-details -fno-finite-loops" } */
 
 void set_color(void);
 void xml_colorize_line(unsigned int *p, int state)
diff --git a/gcc/testsuite/gcc.dg/predict-9.c b/gcc/testsuite/gcc.dg/predict-9.c
index 7e5ba08..f491c51 100644
--- a/gcc/testsuite/gcc.dg/predict-9.c
+++ b/gcc/testsuite/gcc.dg/predict-9.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-profile_estimate" } */
+/* { dg-options "-O2 -fdisable-tree-evrp -fdump-tree-profile_estimate -fno-finite-loops" } */
 
 extern int global;
 extern int global2;
diff --git a/gcc/testsuite/gcc.dg/pure-2.c b/gcc/testsuite/gcc.dg/pure-2.c
index fe6e2bc..318cfd1 100644
--- a/gcc/testsuite/gcc.dg/pure-2.c
+++ b/gcc/testsuite/gcc.dg/pure-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -Wsuggest-attribute=pure" } */
+/* { dg-options "-O2 -Wsuggest-attribute=pure -fno-finite-loops" } */
 /* { dg-add-options bind_pic_locally } */
 
 extern int extern_const(int a) __attribute__ ((pure));
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c b/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c
index d289e5d..a9bdf26 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/20040211-1.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-cddce2" } */
+/* { dg-options "-O2 -fdump-tree-cddce2 -fno-finite-loops" } */
 
 struct rtx_def;
 typedef struct rtx_def *rtx;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c b/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c
new file mode 100644
index 0000000..18c1ddb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/dce-2.c
@@ -0,0 +1,37 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce1 -ffinite-loops" } */
+
+typedef struct list {
+    char pad[15];
+    struct list *next;
+} list;
+
+int data;
+
+list *head, *tail;
+
+int __attribute__((pure)) pfn (int);
+
+int foo (unsigned u, int s)
+{
+  unsigned i;
+  list *p;
+  int j;
+
+  for (i = 0; i < u; i += 2)
+    ;
+
+  for (p = head; p; p = p->next)
+    ;
+
+  for (j = data; j & s; j = pfn (j + 3))
+    ;
+
+  for (p = head; p != tail; p = p->next)
+    for (j = data + 1; j > s; j = pfn (j + 2))
+      ;
+
+  return 0;
+}
+/* { dg-final { scan-tree-dump-not "if" "cddce1"} } */
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c b/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c
index a29c9fb..3d05ad2 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/loop-10.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdump-tree-optimized -fno-finite-loops" } */
 /* { dg-require-effective-target int32plus } */
 
 int bar (void);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c b/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c
index e9b4f26..187c084 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/split-path-6.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fsplit-paths -fno-tree-cselim -fdump-tree-split-paths-details -w" } */
+/* { dg-options "-O2 -fsplit-paths -fno-tree-cselim -fdump-tree-split-paths-details -w -fno-finite-loops" } */
 
 struct __sFILE
 {
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c
index d829b04..6752676 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-12.c
@@ -1,5 +1,5 @@ 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-thread2-details -fdump-tree-thread3-details -fdump-tree-thread4-details" } */
+/* { dg-options "-O2 -fdump-tree-thread2-details -fdump-tree-thread3-details -fdump-tree-thread4-details -fno-finite-loops" } */
 /* { dg-final { scan-tree-dump "FSM" "thread2" } } */
 /* { dg-final { scan-tree-dump "FSM" "thread3" } } */
 /* { dg-final { scan-tree-dump "FSM" "thread4" { xfail *-*-* } } } */
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;
diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 470b6a2..9b9cb41 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -2798,6 +2798,27 @@  finite_loop_p (struct loop *loop)
 		 loop->num);
       return true;
     }
+
+  if (flag_finite_loops)
+    {
+      unsigned i;
+      vec<edge> exits = get_loop_exit_edges (loop);
+      edge ex;
+
+      /* If the loop has a normal exit, we can assume it will terminate.  */
+      FOR_EACH_VEC_ELT (exits, i, ex)
+	if (!(ex->flags & (EDGE_EH | EDGE_ABNORMAL | EDGE_FAKE)))
+	  {
+	    exits.release ();
+	    if (dump_file)
+	      fprintf (dump_file, "Assume loop %i to be finite: it has an exit "
+		       "and -ffinite-loops is on.\n", loop->num);
+	    return true;
+	  }
+
+      exits.release ();
+    }
+
   return false;
 }
 
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c
new file mode 100644
index 0000000..44767cd
--- /dev/null
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/pr84955-1.c
@@ -0,0 +1,31 @@ 
+/* { dg-do compile }  */
+/* { dg-options "-O2 -fdump-tree-cddce2 -ffinite-loops" } */
+
+int
+f1 (void)
+{
+  int i, j;
+
+#pragma acc parallel loop tile(2,3)
+  for (i = 1; i < 10; i++)
+    for (j = 1; j < 10; j++)
+      for (;;)
+	;
+
+  return i + j;
+}
+
+int
+f2 (void)
+{
+  int i, j, k;
+
+#pragma acc parallel loop tile(2,3)
+  for (i = 1; i < 10; i++)
+    for (j = 1; j < 10; j++)
+      for (k = 1; k < 10; k++)
+	;
+
+  return i + j;
+}
+/* { dg-final { scan-tree-dump-not "if" "cddce2"} } */