[committed] Warn about inconsistent OpenACC nested reduction clauses
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Message ID 20191106124148.26041-1-frederik@codesourcery.com
State New
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  • [committed] Warn about inconsistent OpenACC nested reduction clauses
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Commit Message

Harwath, Frederik Nov. 6, 2019, 12:41 p.m. UTC
From: frederik <frederik@138bc75d-0d04-0410-961f-82ee72b054a4>

	OpenACC (cf. OpenACC 2.7, section 2.9.11. "reduction clause";
	this was first clarified by OpenACC 2.6) requires that, if a
	variable is used in reduction clauses on two nested loops, then
	there must be reduction clauses for that variable on all loops
	that are nested in between the two loops and all these reduction
	clauses must use the same operator.
	This commit introduces a check for that property which reports
	warnings if it is violated.

	2019-11-06  Gergö Barany  <gergo@codesourcery.com>
	            Frederik Harwath  <frederik@codesourcery.com>
	            Thomas Schwinge  <thomas@codesourcery.com>

	gcc/
	* omp-low.c (struct omp_context): New fields
	local_reduction_clauses, outer_reduction_clauses.
	(new_omp_context): Initialize these.
	(scan_sharing_clauses): Record reduction clauses on OpenACC constructs.
	(scan_omp_for): Check reduction clauses for incorrect nesting.
	gcc/testsuite/
	* c-c++-common/goacc/nested-reductions-warn.c: New test.
	* c-c++-common/goacc/nested-reductions.c: New test.
	* gfortran.dg/goacc/nested-reductions-warn.f90: New test.
	* gfortran.dg/goacc/nested-reductions.f90: New test.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c:
	Add expected warnings about missing reduction clauses.
	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c:
	Likewise.

	Reviewed-by: Thomas Schwinge <thomas@codesourcery.com>



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@277875 138bc75d-0d04-0410-961f-82ee72b054a4
---
 gcc/ChangeLog                                 |  10 +
 gcc/omp-low.c                                 |  97 +++
 gcc/testsuite/ChangeLog                       |   9 +
 .../goacc/nested-reductions-warn.c            | 525 ++++++++++++++
 .../c-c++-common/goacc/nested-reductions.c    | 420 +++++++++++
 .../goacc/nested-reductions-warn.f90          | 674 ++++++++++++++++++
 .../gfortran.dg/goacc/nested-reductions.f90   | 540 ++++++++++++++
 libgomp/ChangeLog                             |  11 +
 .../par-loop-comb-reduction-1.c               |   2 +-
 .../par-loop-comb-reduction-2.c               |   2 +-
 .../par-loop-comb-reduction-3.c               |   2 +-
 .../par-loop-comb-reduction-4.c               |   2 +-
 12 files changed, 2290 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/goacc/nested-reductions-warn.c
 create mode 100644 gcc/testsuite/c-c++-common/goacc/nested-reductions.c
 create mode 100644 gcc/testsuite/gfortran.dg/goacc/nested-reductions-warn.f90
 create mode 100644 gcc/testsuite/gfortran.dg/goacc/nested-reductions.f90

Comments

Jakub Jelinek Nov. 6, 2019, 1 p.m. UTC | #1
On Wed, Nov 06, 2019 at 01:41:47PM +0100, frederik@codesourcery.com wrote:
> --- a/gcc/omp-low.c
> +++ b/gcc/omp-low.c
> @@ -128,6 +128,12 @@ struct omp_context
>       corresponding tracking loop iteration variables.  */
>    hash_map<tree, tree> *lastprivate_conditional_map;
>  
> +  /* A tree_list of the reduction clauses in this context.  */
> +  tree local_reduction_clauses;
> +
> +  /* A tree_list of the reduction clauses in outer contexts.  */
> +  tree outer_reduction_clauses;

Could there be acc in the name to make it clear it is OpenACC only?

>    /* Nesting depth of this context.  Used to beautify error messages re
>       invalid gotos.  The outermost ctx is depth 1, with depth 0 being
>       reserved for the main body of the function.  */
> @@ -910,6 +916,8 @@ new_omp_context (gimple *stmt, omp_context *outer_ctx)
>        ctx->outer = outer_ctx;
>        ctx->cb = outer_ctx->cb;
>        ctx->cb.block = NULL;
> +      ctx->local_reduction_clauses = NULL;
> +      ctx->outer_reduction_clauses = ctx->outer_reduction_clauses;
>        ctx->depth = outer_ctx->depth + 1;
>      }
>    else
> @@ -925,6 +933,8 @@ new_omp_context (gimple *stmt, omp_context *outer_ctx)
>        ctx->cb.transform_call_graph_edges = CB_CGE_MOVE;
>        ctx->cb.adjust_array_error_bounds = true;
>        ctx->cb.dont_remap_vla_if_no_change = true;
> +      ctx->local_reduction_clauses = NULL;
> +      ctx->outer_reduction_clauses = NULL;

The = NULL assignments are unnecessary in all 3 cases, ctx is allocated with
XCNEW.
>        ctx->depth = 1;
>      }
>  
> @@ -1139,6 +1149,11 @@ scan_sharing_clauses (tree clauses, omp_context *ctx)
>  	  goto do_private;
>  
>  	case OMP_CLAUSE_REDUCTION:
> +	  if (is_oacc_parallel (ctx) || is_oacc_kernels (ctx))
> +	    ctx->local_reduction_clauses
> +	      = tree_cons (NULL, c, ctx->local_reduction_clauses);

I'm not sure it is a good idea to use a TREE_LIST in this case, vec would be
more natural, wouldn't it.
Or, wouldn't it be better to do this checking in the gimplifier instead of
omp-low.c?  There we have splay trees with GOVD_REDUCTION etc. for the
variables, so it wouldn't be O(#reductions^2) compile time?
It is true that the gimplifier doesn't record the reduction codes (after
all, OpenMP has UDRs and so there can be fairly arbitrary reductions).
Consider million reduction clauses on nested loops.
If gimplifier is not the right spot, then use a splay tree + vector instead?
splay tree for the outer ones, vector for the local ones, and put into both
the clauses, so you can compare reduction code etc.

	Jakub
Harwath, Frederik Nov. 8, 2019, 6:41 a.m. UTC | #2
Hi Jakub,

On 06.11.19 14:00, Jakub Jelinek wrote:
> On Wed, Nov 06, 2019 at 01:41:47PM +0100, frederik@codesourcery.com wrote:
>> --- a/gcc/omp-low.c
>> +++ b/gcc/omp-low.c
>> @@ -128,6 +128,12 @@ struct omp_context
>> [...]
>> +  /* A tree_list of the reduction clauses in this context.  */
>> +  tree local_reduction_clauses;
>> +
>> +  /* A tree_list of the reduction clauses in outer contexts.  */
>> +  tree outer_reduction_clauses;
> 
> Could there be acc in the name to make it clear it is OpenACC only?

Yes, will be added.


>> @@ -910,6 +916,8 @@ new_omp_context (gimple *stmt, omp_context *outer_ctx)
>> [...]
>> +      ctx->local_reduction_clauses = NULL;
>> [...]
>> @@ -925,6 +933,8 @@ new_omp_context (gimple *stmt, omp_context *outer_ctx)
>> [...]
>> +      ctx->local_reduction_clauses = NULL;
>> +      ctx->outer_reduction_clauses = NULL;
> 
> The = NULL assignments are unnecessary in all 3 cases, ctx is allocated with
> XCNEW.

Ok, will be removed.

>> @@ -1139,6 +1149,11 @@ scan_sharing_clauses (tree clauses, omp_context *ctx)
>>  	  goto do_private;
>>  
>>  	case OMP_CLAUSE_REDUCTION:
>> +	  if (is_oacc_parallel (ctx) || is_oacc_kernels (ctx))
>> +	    ctx->local_reduction_clauses
>> +	      = tree_cons (NULL, c, ctx->local_reduction_clauses);
> 
> I'm not sure it is a good idea to use a TREE_LIST in this case, vec would be
> more natural, wouldn't it.

Yes.

> Or, wouldn't it be better to do this checking in the gimplifier instead of
> omp-low.c?  There we have splay trees with GOVD_REDUCTION etc. for the
> variables, so it wouldn't be O(#reductions^2) compile time> It is true that the gimplifier doesn't record the reduction codes (after
> all, OpenMP has UDRs and so there can be fairly arbitrary reductions).


Right, I have considered moving the implementation somewhere else before.
I am going to look into this, but perhaps we will just keep it where it is
if otherwise the implementation becomes more complicated.

> Consider million reduction clauses on nested loops.
> If gimplifier is not the right spot, then use a splay tree + vector instead?
> splay tree for the outer ones, vector for the local ones, and put into both
> the clauses, so you can compare reduction code etc.

Sounds like a good idea. I am going to try that.
However, I have not seen the suboptimal data structure choices
of the original patch as a problem, since the case of million reduction clauses
has not occurred to me.

Thank you for your feedback!

Best regards,
Frederik

Patch
diff mbox series

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7fee0f37e9bf..38160dd631e9 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@ 
+2019-11-06  Gergö Barany  <gergo@codesourcery.com>
+	    Frederik Harwath  <frederik@codesourcery.com>
+	    Thomas Schwinge  <thomas@codesourcery.com>
+
+	* omp-low.c (struct omp_context): New fields
+	local_reduction_clauses, outer_reduction_clauses.
+	(new_omp_context): Initialize these.
+	(scan_sharing_clauses): Record reduction clauses on OpenACC constructs.
+	(scan_omp_for): Check reduction clauses for incorrect nesting.
+	
 2019-11-06  Jakub Jelinek  <jakub@redhat.com>
 
 	PR inline-asm/92352
diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 122f42788813..fa76ceba33c6 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -128,6 +128,12 @@  struct omp_context
      corresponding tracking loop iteration variables.  */
   hash_map<tree, tree> *lastprivate_conditional_map;
 
+  /* A tree_list of the reduction clauses in this context.  */
+  tree local_reduction_clauses;
+
+  /* A tree_list of the reduction clauses in outer contexts.  */
+  tree outer_reduction_clauses;
+
   /* Nesting depth of this context.  Used to beautify error messages re
      invalid gotos.  The outermost ctx is depth 1, with depth 0 being
      reserved for the main body of the function.  */
@@ -910,6 +916,8 @@  new_omp_context (gimple *stmt, omp_context *outer_ctx)
       ctx->outer = outer_ctx;
       ctx->cb = outer_ctx->cb;
       ctx->cb.block = NULL;
+      ctx->local_reduction_clauses = NULL;
+      ctx->outer_reduction_clauses = ctx->outer_reduction_clauses;
       ctx->depth = outer_ctx->depth + 1;
     }
   else
@@ -925,6 +933,8 @@  new_omp_context (gimple *stmt, omp_context *outer_ctx)
       ctx->cb.transform_call_graph_edges = CB_CGE_MOVE;
       ctx->cb.adjust_array_error_bounds = true;
       ctx->cb.dont_remap_vla_if_no_change = true;
+      ctx->local_reduction_clauses = NULL;
+      ctx->outer_reduction_clauses = NULL;
       ctx->depth = 1;
     }
 
@@ -1139,6 +1149,11 @@  scan_sharing_clauses (tree clauses, omp_context *ctx)
 	  goto do_private;
 
 	case OMP_CLAUSE_REDUCTION:
+	  if (is_oacc_parallel (ctx) || is_oacc_kernels (ctx))
+	    ctx->local_reduction_clauses
+	      = tree_cons (NULL, c, ctx->local_reduction_clauses);
+	  /* FALLTHRU */
+
 	case OMP_CLAUSE_IN_REDUCTION:
 	  decl = OMP_CLAUSE_DECL (c);
 	  if (TREE_CODE (decl) == MEM_REF)
@@ -2423,6 +2438,88 @@  scan_omp_for (gomp_for *stmt, omp_context *outer_ctx)
 	  gimple_omp_for_set_clauses (stmt, clauses);
 	  check_oacc_kernel_gwv (stmt, ctx);
 	}
+
+      /* Collect all variables named in reductions on this loop.  Ensure
+	 that, if this loop has a reduction on some variable v, and there is
+	 a reduction on v somewhere in an outer context, then there is a
+	 reduction on v on all intervening loops as well.  */
+      tree local_reduction_clauses = NULL;
+      for (tree c = gimple_omp_for_clauses (stmt); c; c = OMP_CLAUSE_CHAIN (c))
+	{
+	  if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_REDUCTION)
+	    local_reduction_clauses
+	      = tree_cons (NULL, c, local_reduction_clauses);
+	}
+      if (ctx->outer_reduction_clauses == NULL && ctx->outer != NULL)
+	ctx->outer_reduction_clauses
+	  = chainon (unshare_expr (ctx->outer->local_reduction_clauses),
+		     ctx->outer->outer_reduction_clauses);
+      tree outer_reduction_clauses = ctx->outer_reduction_clauses;
+      tree local_iter = local_reduction_clauses;
+      for (; local_iter; local_iter = TREE_CHAIN (local_iter))
+	{
+	  tree local_clause = TREE_VALUE (local_iter);
+	  tree local_var = OMP_CLAUSE_DECL (local_clause);
+	  tree_code local_op = OMP_CLAUSE_REDUCTION_CODE (local_clause);
+	  bool have_outer_reduction = false;
+	  tree ctx_iter = outer_reduction_clauses;
+	  for (; ctx_iter; ctx_iter = TREE_CHAIN (ctx_iter))
+	    {
+	      tree outer_clause = TREE_VALUE (ctx_iter);
+	      tree outer_var = OMP_CLAUSE_DECL (outer_clause);
+	      tree_code outer_op = OMP_CLAUSE_REDUCTION_CODE (outer_clause);
+	      if (outer_var == local_var && outer_op != local_op)
+		{
+		  warning_at (gimple_location (stmt), 0,
+			      "conflicting reduction operations for %qE",
+			      local_var);
+		  inform (OMP_CLAUSE_LOCATION (outer_clause),
+			  "location of the previous reduction for %qE",
+			  outer_var);
+		}
+	      if (outer_var == local_var)
+		{
+		  have_outer_reduction = true;
+		  break;
+		}
+	    }
+	  if (have_outer_reduction)
+	    {
+	      /* There is a reduction on outer_var both on this loop and on
+		 some enclosing loop.  Walk up the context tree until such a
+		 loop with a reduction on outer_var is found, and complain
+		 about all intervening loops that do not have such a
+		 reduction.  */
+	      struct omp_context *curr_loop = ctx->outer;
+	      bool found = false;
+	      while (curr_loop != NULL)
+		{
+		  tree curr_iter = curr_loop->local_reduction_clauses;
+		  for (; curr_iter; curr_iter = TREE_CHAIN (curr_iter))
+		    {
+		      tree curr_clause = TREE_VALUE (curr_iter);
+		      tree curr_var = OMP_CLAUSE_DECL (curr_clause);
+		      if (curr_var == local_var)
+			{
+			  found = true;
+			  break;
+			}
+		    }
+		  if (!found)
+		    warning_at (gimple_location (curr_loop->stmt), 0,
+				"nested loop in reduction needs "
+				"reduction clause for %qE",
+				local_var);
+		  else
+		    break;
+		  curr_loop = curr_loop->outer;
+		}
+	    }
+	}
+      ctx->local_reduction_clauses = local_reduction_clauses;
+      ctx->outer_reduction_clauses
+	= chainon (unshare_expr (ctx->local_reduction_clauses),
+		   ctx->outer_reduction_clauses);
     }
 
   scan_sharing_clauses (clauses, ctx);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a0f52ec2c5cd..64568e5661af 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,12 @@ 
+2019-11-06  Gergö Barany  <gergo@codesourcery.com>
+	    Frederik Harwath  <frederik@codesourcery.com>
+	    Thomas Schwinge  <thomas@codesourcery.com>
+
+	* c-c++-common/goacc/nested-reductions-warn.c: New test.
+	* c-c++-common/goacc/nested-reductions.c: New test.
+	* gfortran.dg/goacc/nested-reductions-warn.f90: New test.
+	* gfortran.dg/goacc/nested-reductions.f90: New test.
+
 2019-11-06  Jakub Jelinek  <jakub@redhat.com>
 
 	PR inline-asm/92352
diff --git a/gcc/testsuite/c-c++-common/goacc/nested-reductions-warn.c b/gcc/testsuite/c-c++-common/goacc/nested-reductions-warn.c
new file mode 100644
index 000000000000..e2af66e4fa3b
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/goacc/nested-reductions-warn.c
@@ -0,0 +1,525 @@ 
+/* Test erroneous cases of nested reduction loops.  */
+
+void acc_parallel (void)
+{
+  int i, j, k, l, sum, diff;
+
+  #pragma acc parallel
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." } 
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(-:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(+:sum) // { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but using a combined parallel loop construct.  */
+
+void acc_parallel_loop (void)
+{
+  int i, j, k, l, sum, diff;
+
+  #pragma acc parallel loop
+  for (int h = 0; h < 10; ++h)
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(-:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(+:sum) // { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but now the outermost reduction clause is on
+   the parallel region, not the outermost loop.  */
+void acc_parallel_reduction (void)
+{
+  int i, j, k, l, sum, diff;
+
+  #pragma acc parallel reduction(+:sum)
+  {
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(-:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(max:sum) // { dg-warning "conflicting reduction operations for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(max:sum) // { dg-warning "conflicting reduction operations for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+      #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." })
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+	for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(+:sum) // { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but using a combined parallel loop construct, and
+   the outermost reduction clause is on that one, not the outermost loop.  */
+void acc_parallel_loop_reduction (void)
+{
+  int i, j, k, l, sum, diff;
+
+  #pragma acc parallel loop reduction(+:sum)
+  for (int h = 0; h < 10; ++h)
+  {
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(-:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(max:sum) // { dg-warning "conflicting reduction operations for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(max:sum) // { dg-warning "conflicting reduction operations for .sum." }
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+      for (j = 0; j < 10; j++)
+      #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." })
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(+:sum) // { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but inside a routine construct.  */
+#pragma acc routine gang
+void acc_routine (void)
+{
+  int i, j, k, l, sum, diff;
+
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+	for (k = 0; k < 10; k++)
+          #pragma acc loop reduction(+:sum)
+          for (l = 0; l < 10; l++)
+            sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." }
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(-:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum) // { dg-warning "conflicting reduction operations for .sum." }
+      for (j = 0; j < 10; j++)
+      #pragma acc loop reduction(+:sum) // { dg-warning "conflicting reduction operations for .sum." })
+      // { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 } 
+        for (k = 0; k < 10; k++)
+	  #pragma acc loop reduction(*:sum) // { dg-warning "conflicting reduction operations for .sum." }
+	  for (l = 0; l < 10; l++)
+	    sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(-:diff) // { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(+:sum) // { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+void acc_kernels (void)
+{
+  int i, j, k, sum, diff;
+
+  /* FIXME:  No diagnostics are produced for these loops because reductions
+     in kernels regions are not supported yet.  */
+  #pragma acc kernels
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:diff)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(-:sum)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+  }
+}
diff --git a/gcc/testsuite/c-c++-common/goacc/nested-reductions.c b/gcc/testsuite/c-c++-common/goacc/nested-reductions.c
new file mode 100644
index 000000000000..15385c4da992
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/goacc/nested-reductions.c
@@ -0,0 +1,420 @@ 
+/* Test cases of nested reduction loops that should compile cleanly.  */
+
+void acc_parallel (void)
+{
+  int i, j, k, sum, diff;
+
+  #pragma acc parallel
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop collapse(2) reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but using a combined parallel loop construct.  */
+
+void acc_parallel_loop (void)
+{
+  int i, j, k, l, sum, diff;
+
+  #pragma acc parallel loop
+  for (int h = 0; h < 10; ++h)
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop collapse(2) reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but now the outermost reduction clause is on
+   the parallel region, not the outermost loop.  */
+
+void acc_parallel_reduction (void)
+{
+  int i, j, k, sum, diff;
+
+  #pragma acc parallel reduction(+:sum)
+  {
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    for (i = 0; i < 10; i++)
+      #pragma acc loop
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but using a combined parallel loop construct, and
+   the outermost reduction clause is on that one, not the outermost loop.  */
+void acc_parallel_loop_reduction (void)
+{
+  int i, j, k, sum, diff;
+
+  #pragma acc parallel loop reduction(+:sum)
+  for (int h = 0; h < 10; ++h)
+  {
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    for (i = 0; i < 10; i++)
+      #pragma acc loop
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum) // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop // { dg-warning "insufficient partitioning available to parallelize loop" }
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+/* The same tests as above, but inside a routine construct.  */
+#pragma acc routine gang
+void acc_routine (void)
+{
+  int i, j, k, sum, diff;
+
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop collapse(2) reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop collapse(2) reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum) reduction(-:diff)
+    for (i = 0; i < 10; i++)
+      {
+        #pragma acc loop reduction(+:sum)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(+:sum)
+          for (k = 0; k < 10; k++)
+            sum = 1;
+
+        #pragma acc loop reduction(-:diff)
+        for (j = 0; j < 10; j++)
+          #pragma acc loop reduction(-:diff)
+          for (k = 0; k < 10; k++)
+            diff = 1;
+      }
+  }
+}
+
+void acc_kernels (void)
+{
+  int i, j, k, sum, diff;
+
+  /* FIXME:  These tests are not meaningful yet because reductions in
+     kernels regions are not supported yet.  */
+  #pragma acc kernels
+  {
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+
+    #pragma acc loop reduction(+:sum)
+    for (i = 0; i < 10; i++)
+      #pragma acc loop reduction(+:sum)
+      for (j = 0; j < 10; j++)
+        #pragma acc loop reduction(+:sum)
+        for (k = 0; k < 10; k++)
+          sum = 1;
+  }
+}
diff --git a/gcc/testsuite/gfortran.dg/goacc/nested-reductions-warn.f90 b/gcc/testsuite/gfortran.dg/goacc/nested-reductions-warn.f90
new file mode 100644
index 000000000000..ec36bc9616e0
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/goacc/nested-reductions-warn.f90
@@ -0,0 +1,674 @@ 
+! Test erroneous cases of nested reduction loops.
+
+subroutine acc_parallel ()
+  implicit none (type, external)
+  integer :: i, j, k, l, sum, diff
+
+  !$acc parallel
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(-:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(+:sum)  ! { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  !$acc end parallel
+end subroutine acc_parallel
+
+! The same tests as above, but using a combined parallel loop construct.
+
+subroutine acc_parallel_loop ()
+  implicit none (type, external)
+  integer :: h, i, j, k, l, sum, diff
+
+  !$acc parallel loop
+  do h = 1, 10
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(-:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(+:sum)  ! { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  end do
+end subroutine acc_parallel_loop
+
+! The same tests as above, but now the outermost reduction clause is on
+! the parallel region, not the outermost loop.
+
+subroutine acc_parallel_reduction ()
+  implicit none (type, external)
+  integer :: i, j, k, l, sum, diff
+
+  !$acc parallel reduction(+:sum)
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop collapse(2)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(-:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(max:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(max:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(+:sum)  ! { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  !$acc end parallel
+end subroutine acc_parallel_reduction
+
+! The same tests as above, but using a combined parallel loop construct, and
+! the outermost reduction clause is on that one, not the outermost loop.  */
+subroutine acc_parallel_loop_reduction ()
+  implicit none (type, external)
+  integer :: h, i, j, k, l, sum, diff
+
+  !$acc parallel loop reduction(+:sum)
+  do h = 1, 10
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop collapse(2)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }  
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(-:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(max:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(max:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+    do i = 1, 10
+      !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(+:sum)  ! { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+      ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  end do
+end subroutine acc_parallel_loop_reduction
+
+! The same tests as above, but inside a routine construct.
+subroutine acc_routine ()
+  implicit none (type, external)
+  !$acc routine gang
+  integer :: i, j, k, l, sum, diff
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(+:sum)
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(-:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+        ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
+        do k = 1, 10
+          !$acc loop reduction(*:sum)  ! { dg-warning "conflicting reduction operations for .sum." }
+          do l = 1, 10
+            sum = 1
+          end do
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(-:diff)  ! { dg-warning "nested loop in reduction needs reduction clause for .sum." }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(+:sum)  ! { dg-warning "nested loop in reduction needs reduction clause for .diff." }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+            diff = 1
+        end do
+      end do
+    end do
+end subroutine acc_routine
+
+subroutine acc_kernels ()
+  integer :: i, j, k, sum, diff
+
+  ! FIXME:  No diagnostics are produced for these loops because reductions
+  ! in kernels regions are not supported yet.
+  !$acc kernels
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:diff)
+      do j = 1, 10
+        !$acc loop
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(-:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+  !$acc end kernels
+end subroutine acc_kernels
diff --git a/gcc/testsuite/gfortran.dg/goacc/nested-reductions.f90 b/gcc/testsuite/gfortran.dg/goacc/nested-reductions.f90
new file mode 100644
index 000000000000..3becafabe622
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/goacc/nested-reductions.f90
@@ -0,0 +1,540 @@ 
+! Test cases of nested reduction loops that should compile cleanly.
+
+subroutine acc_parallel ()
+  implicit none (type, external)
+  integer :: i, j, k, sum, diff
+
+  !$acc parallel
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop collapse(2) reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2) reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  !$acc end parallel
+end subroutine acc_parallel
+
+! The same tests as above, but using a combined parallel loop construct.
+
+subroutine acc_parallel_loop ()
+  implicit none (type, external)
+  integer :: h, i, j, k, l, sum, diff
+
+  !$acc parallel loop
+  do h = 1, 10
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop collapse(2) reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2) reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  end do
+end subroutine acc_parallel_loop
+
+! The same tests as above, but now the outermost reduction clause is on
+! the parallel region, not the outermost loop.  */
+
+subroutine acc_parallel_reduction ()
+  implicit none (type, external)
+  integer :: i, j, k, sum, diff
+
+  !$acc parallel reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    do i = 1, 10
+      !$acc loop
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  !$acc end parallel
+end subroutine acc_parallel_reduction
+
+! The same tests as above, but using a combined parallel loop construct, and
+! the outermost reduction clause is on that one, not the outermost loop.  */
+subroutine acc_parallel_loop_reduction ()
+  implicit none (type, external)
+  integer :: h, i, j, k, sum, diff
+
+  !$acc parallel loop reduction(+:sum)
+  do h = 1, 10
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    do i = 1, 10
+      !$acc loop
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop  ! { dg-warning "insufficient partitioning available to parallelize loop" }
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+  end do
+end subroutine acc_parallel_loop_reduction
+
+! The same tests as above, but inside a routine construct.
+subroutine acc_routine ()
+  implicit none (type, external)
+  !$acc routine gang
+
+  integer :: i, j, k, sum, diff
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop collapse(2) reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop collapse(2) reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum) reduction(-:diff)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+
+      !$acc loop reduction(-:diff)
+      do j = 1, 10
+        !$acc loop reduction(-:diff)
+        do k = 1, 10
+          diff = 1
+        end do
+      end do
+    end do
+end subroutine acc_routine
+
+subroutine acc_kernels ()
+  implicit none (type, external)
+  integer :: i, j, k, sum, diff
+
+  ! FIXME:  These tests are not meaningful yet because reductions in
+  ! kernels regions are not supported yet.
+  !$acc kernels
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+
+    !$acc loop reduction(+:sum)
+    do i = 1, 10
+      !$acc loop reduction(+:sum)
+      do j = 1, 10
+        !$acc loop reduction(+:sum)
+        do k = 1, 10
+          sum = 1
+        end do
+      end do
+    end do
+
+  !$acc end kernels
+end subroutine acc_kernels
diff --git a/libgomp/ChangeLog b/libgomp/ChangeLog
index 15521b48bd88..067d247da9ac 100644
--- a/libgomp/ChangeLog
+++ b/libgomp/ChangeLog
@@ -1,3 +1,14 @@ 
+2019-11-06  Thomas Schwinge  <thomas@codesourcery.com>
+
+	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c:
+	Add expected warnings about missing reduction clauses.
+	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c:
+	Likewise.
+	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c:
+	Likewise.
+	* testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c:
+	Likewise.
+
 2019-11-04  Tobias Burnus  <tobias@codesourcery.com>
 
 	* testsuite/libgomp.fortran/pr66199-1.f90: Remove
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c
index 5e82e1d350cc..8c08717fdf2c 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-1.c
@@ -15,7 +15,7 @@  main (int argc, char *argv[])
   #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32) \
     reduction(+:res) copy(res)
   {
-    #pragma acc loop gang
+    #pragma acc loop gang /* { dg-warning "nested loop in reduction needs reduction clause for 'res'" "TODO" } */
     for (j = 0; j < 32; j++)
       {
 	#pragma acc loop worker reduction(+:res)
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c
index a339f327956e..41042accbde5 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-2.c
@@ -14,7 +14,7 @@  main (int argc, char *argv[])
   #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32) \
 		       reduction(^:res)
   {
-    #pragma acc loop gang
+    #pragma acc loop gang /* { dg-warning "nested loop in reduction needs reduction clause for 'res'" "TODO" } */
     for (j = 0; j < 32; j++)
       {
 	#pragma acc loop worker vector reduction(^:res)
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c
index 6369d7fbb330..ace1e005e2e2 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-3.c
@@ -16,7 +16,7 @@  main (int argc, char *argv[])
   #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32) \
     reduction(+:res) copy(res)
   {
-    #pragma acc loop gang
+    #pragma acc loop gang /* { dg-warning "nested loop in reduction needs reduction clause for 'res'" "TODO" } */
     for (j = 0; j < 32; j++)
       {
 	#pragma acc loop worker vector reduction(+:res)
diff --git a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c
index 140c32263278..c3cc12fa953a 100644
--- a/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c
+++ b/libgomp/testsuite/libgomp.oacc-c-c++-common/par-loop-comb-reduction-4.c
@@ -16,7 +16,7 @@  main (int argc, char *argv[])
   #pragma acc parallel num_gangs(32) num_workers(32) vector_length(32) \
     reduction(+:res) reduction(max:mres) copy(res, mres)
   {
-    #pragma acc loop gang
+    #pragma acc loop gang /* { dg-warning "nested loop in reduction needs reduction clause for 'm\?res'" "TODO" } */
     for (j = 0; j < 32; j++)
       {
 	#pragma acc loop worker vector reduction(+:res) reduction(max:mres)