[PATCH v2] Re: OpenMP: Generate SIMD clones for functions with "declare target"

[Sandra Loosemore <sandra@codesourcery.com>]

[-- Attachment #1: Type: text/plain, Size: 1432 bytes --]

On 9/14/22 12:12, Jakub Jelinek wrote:

> If it is pure optimization thing and purely keyed on the definition,
> all the simd clones should be local to the TU, never exported from it.

OK, here is a revised patch that addresses that.  x86_64 target also 
generates a different set of clones for functions with internal linkage 
vs external so I hacked that to treat these implicit clones in the same 
way as other internal clones.

There is an existing problem with internal "declare simd" clones in that 
nothing ever DCEs clones that end up not being useful, or does a scan of 
the code in the compilation unit before clone generation to avoid 
generating useless clones in the first place.  I haven't tried to solve 
that problem, but I did attempt to mitigate it for these implicit 
"declare target" clones by tagging the option 
OPT_LEVELS_2_PLUS_SPEED_ONLY (instead of enabling it by default all the 
time) so the clones are not generated by default at -Os and -Og.  I 
added a couple new test cases to check this.

On 9/14/22 15:45, Thomas Schwinge wrote:
> However, OpenACC and OpenMP support may be active at the same time...
> 
>> +  if (attr == NULL_TREE
>> +      && flag_openmp_target_simd_clone && !flag_openacc)
> 
> ..., so '!flag_openacc' is not the right check here.  Instead you'd do
> '!oacc_get_fn_attrib (DECL_ATTRIBUTES (node->decl))' (untested) or
> similar.

This is fixed now too.

OK to check in?

-Sandra

[-- Attachment #2: declare-target-simd-clones-v2.patch --]
[-- Type: text/x-patch, Size: 28028 bytes --]

From dfdb9a2162978b964863f351c814211dca8e9a3f Mon Sep 17 00:00:00 2001
From: Sandra Loosemore <sandra@codesourcery.com>
Date: Thu, 22 Sep 2022 02:16:42 +0000
Subject: [PATCH] OpenMP: Generate SIMD clones for functions with "declare
 target"

This patch causes the IPA simdclone pass to generate clones for
functions with the "omp declare target" attribute as if they had
"omp declare simd", provided the function appears to be suitable for
SIMD execution.  The filter is conservative, rejecting functions
that write memory or that call other functions not known to be safe.
A new option -fopenmp-target-simd-clone is added to control this
transformation; it's enabled at -O2 and higher.

gcc/ChangeLog:

	* common.opt (fopenmp-target-simd-clone): New option.
	* opts.cc (default_options_table): Add -fopenmp-target-simd-clone.
	* doc/invoke.texi (-fopenmp-target-simd-clone): Document.
	* omp-simd-clone.cc (auto_simd_check_stmt): New function.
	(mark_auto_simd_clone): New function.
	(simd_clone_create): Add force_local argument, make the symbol
	have internal linkage if it is true.
	(expand_simd_clones): Also check for cloneable functions with
	"omp declare target".  Pass explicit_p argument to
	simd_clone.compute_vecsize_and_simdlen target hook.
	* target.def (TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN):
	Add bool explicit_p argument.
	* doc/tm.texi: Regenerated.
	* config/aarch64/aarch64.cc
	(aarch64_simd_clone_compute_vecsize_and_simdlen): Update.
	* config/gcn/gcn.cc
	(gcn_simd_clone_compute_vecsize_and_simdlen): Update.
	* config/i386/i386.cc
	(ix86_simd_clone_compute_vecsize_and_simdlen): Update.

gcc/testsuite/ChangeLog:

	* gcc.dg/gomp/target-simd-clone-1.c: New.
	* gcc.dg/gomp/target-simd-clone-2.c: New.
	* gcc.dg/gomp/target-simd-clone-3.c: New.
	* gcc.dg/gomp/target-simd-clone-4.c: New.
	* gcc.dg/gomp/target-simd-clone-5.c: New.
	* gcc.dg/gomp/target-simd-clone-6.c: New.
---
 gcc/common.opt                                |   4 +
 gcc/config/aarch64/aarch64.cc                 |  24 +-
 gcc/config/gcn/gcn.cc                         |  10 +-
 gcc/config/i386/i386.cc                       |  27 +-
 gcc/doc/invoke.texi                           |  12 +-
 gcc/doc/tm.texi                               |   2 +-
 gcc/omp-simd-clone.cc                         | 237 ++++++++++++++++--
 gcc/opts.cc                                   |   1 +
 gcc/target.def                                |   2 +-
 .../gcc.dg/gomp/target-simd-clone-1.c         |  18 ++
 .../gcc.dg/gomp/target-simd-clone-2.c         |  18 ++
 .../gcc.dg/gomp/target-simd-clone-3.c         |  17 ++
 .../gcc.dg/gomp/target-simd-clone-4.c         |  16 ++
 .../gcc.dg/gomp/target-simd-clone-5.c         |  13 +
 .../gcc.dg/gomp/target-simd-clone-6.c         |  13 +
 15 files changed, 362 insertions(+), 52 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-2.c
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-3.c
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-4.c
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-5.c
 create mode 100644 gcc/testsuite/gcc.dg/gomp/target-simd-clone-6.c

diff --git a/gcc/common.opt b/gcc/common.opt
index fba90ff6dcb..c735c62a8d4 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2217,6 +2217,10 @@ fomit-frame-pointer
 Common Var(flag_omit_frame_pointer) Optimization
 When possible do not generate stack frames.
 
+fopenmp-target-simd-clone
+Common Var(flag_openmp_target_simd_clone) Optimization
+Generate SIMD clones for functions with the OpenMP declare target directive.
+
 fopt-info
 Common Var(flag_opt_info) Optimization
 Enable all optimization info dumps on stderr.
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index f199e77cd42..c6d282c55ef 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -26612,7 +26612,8 @@ currently_supported_simd_type (tree t, tree b)
 static int
 aarch64_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 					struct cgraph_simd_clone *clonei,
-					tree base_type, int num)
+					tree base_type, int num,
+					bool explicit_p)
 {
   tree t, ret_type;
   unsigned int elt_bits, count;
@@ -26630,8 +26631,9 @@ aarch64_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 	  || const_simdlen > 1024
 	  || (const_simdlen & (const_simdlen - 1)) != 0))
     {
-      warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		  "unsupported simdlen %wd", const_simdlen);
+      if (explicit_p)
+	warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+		    "unsupported simdlen %wd", const_simdlen);
       return 0;
     }
 
@@ -26639,7 +26641,9 @@ aarch64_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
   if (TREE_CODE (ret_type) != VOID_TYPE
       && !currently_supported_simd_type (ret_type, base_type))
     {
-      if (TYPE_SIZE (ret_type) != TYPE_SIZE (base_type))
+      if (!explicit_p)
+	;
+      else if (TYPE_SIZE (ret_type) != TYPE_SIZE (base_type))
 	warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
 		    "GCC does not currently support mixed size types "
 		    "for %<simd%> functions");
@@ -26666,7 +26670,9 @@ aarch64_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
       if (clonei->args[i].arg_type != SIMD_CLONE_ARG_TYPE_UNIFORM
 	  && !currently_supported_simd_type (arg_type, base_type))
 	{
-	  if (TYPE_SIZE (arg_type) != TYPE_SIZE (base_type))
+	  if (!explicit_p)
+	    ;
+	  else if (TYPE_SIZE (arg_type) != TYPE_SIZE (base_type))
 	    warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
 			"GCC does not currently support mixed size types "
 			"for %<simd%> functions");
@@ -26696,9 +26702,11 @@ aarch64_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
       if (clonei->simdlen.is_constant (&const_simdlen)
 	  && maybe_ne (vec_bits, 64U) && maybe_ne (vec_bits, 128U))
 	{
-	  warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		      "GCC does not currently support simdlen %wd for type %qT",
-		      const_simdlen, base_type);
+	  if (explicit_p)
+	    warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+			"GCC does not currently support simdlen %wd for "
+			"type %qT",
+			const_simdlen, base_type);
 	  return 0;
 	}
     }
diff --git a/gcc/config/gcn/gcn.cc b/gcc/config/gcn/gcn.cc
index ceb69000807..5c80b8df852 100644
--- a/gcc/config/gcn/gcn.cc
+++ b/gcc/config/gcn/gcn.cc
@@ -4562,7 +4562,8 @@ static int
 gcn_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *ARG_UNUSED (node),
 					    struct cgraph_simd_clone *clonei,
 					    tree base_type,
-					    int ARG_UNUSED (num))
+					    int ARG_UNUSED (num),
+					    bool explicit_p)
 {
   unsigned int elt_bits = GET_MODE_BITSIZE (SCALAR_TYPE_MODE (base_type));
 
@@ -4572,9 +4573,10 @@ gcn_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *ARG_UNUSED (node
     {
       /* Note that x86 has a similar message that is likely to trigger on
 	 sizes that are OK for gcn; the user can't win.  */
-      warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		  "unsupported simdlen %wd (amdgcn)",
-		  clonei->simdlen.to_constant ());
+      if (explicit_p)
+	warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+		    "unsupported simdlen %wd (amdgcn)",
+		    clonei->simdlen.to_constant ());
       return 0;
     }
 
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index c4d0e36e9c0..99ae388ad56 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -23647,7 +23647,8 @@ ix86_memmodel_check (unsigned HOST_WIDE_INT val)
 static int
 ix86_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 					     struct cgraph_simd_clone *clonei,
-					     tree base_type, int num)
+					     tree base_type, int num,
+					     bool explicit_p)
 {
   int ret = 1;
 
@@ -23656,8 +23657,9 @@ ix86_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 	  || clonei->simdlen > 1024
 	  || (clonei->simdlen & (clonei->simdlen - 1)) != 0))
     {
-      warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		  "unsupported simdlen %wd", clonei->simdlen.to_constant ());
+      if (explicit_p)
+	warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+		    "unsupported simdlen %wd", clonei->simdlen.to_constant ());
       return 0;
     }
 
@@ -23677,8 +23679,9 @@ ix86_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 	  break;
 	/* FALLTHRU */
       default:
-	warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		    "unsupported return type %qT for simd", ret_type);
+	if (explicit_p)
+	  warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+		      "unsupported return type %qT for simd", ret_type);
 	return 0;
       }
 
@@ -23707,13 +23710,14 @@ ix86_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 	default:
 	  if (clonei->args[i].arg_type == SIMD_CLONE_ARG_TYPE_UNIFORM)
 	    break;
-	  warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		      "unsupported argument type %qT for simd", arg_type);
+	  if (explicit_p)
+	    warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+			"unsupported argument type %qT for simd", arg_type);
 	  return 0;
 	}
     }
 
-  if (!TREE_PUBLIC (node->decl))
+  if (!TREE_PUBLIC (node->decl) || !explicit_p)
     {
       /* If the function isn't exported, we can pick up just one ISA
 	 for the clones.  */
@@ -23784,9 +23788,10 @@ ix86_simd_clone_compute_vecsize_and_simdlen (struct cgraph_node *node,
 	cnt /= clonei->vecsize_float;
       if (cnt > (TARGET_64BIT ? 16 : 8))
 	{
-	  warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
-		      "unsupported simdlen %wd",
-		      clonei->simdlen.to_constant ());
+	  if (explicit_p)
+	    warning_at (DECL_SOURCE_LOCATION (node->decl), 0,
+			"unsupported simdlen %wd",
+			clonei->simdlen.to_constant ());
 	  return 0;
 	}
       }
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 8def6baa904..e05739a334c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -204,7 +204,7 @@ in the following sections.
 -flax-vector-conversions  -fms-extensions @gol
 -foffload=@var{arg}  -foffload-options=@var{arg} @gol
 -fopenacc  -fopenacc-dim=@var{geom} @gol
--fopenmp  -fopenmp-simd @gol
+-fopenmp  -fopenmp-simd  -fopenmp-target-simd-clone @gol
 -fpermitted-flt-eval-methods=@var{standard} @gol
 -fplan9-extensions  -fsigned-bitfields  -funsigned-bitfields @gol
 -fsigned-char  -funsigned-char  -fsso-struct=@var{endianness}}
@@ -2749,6 +2749,16 @@ Enable handling of OpenMP's SIMD directives with @code{#pragma omp}
 in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives
 are ignored.
 
+@item -fopenmp-target-simd-clone
+@opindex fopenmp-target-simd-clone
+@cindex OpenMP target SIMD clone
+In addition to generating SIMD clones for functions marked with the
+@code{declare simd} directive, GCC also generates clones
+for functions marked with the OpenMP @code{declare target} directive
+that are suitable for vectorization when this option is in effect.
+It is enabled by default at @option{-O2} and higher (but not @option{-Os}
+or @option{-Og}).
+
 @item -fpermitted-flt-eval-methods=@var{style}
 @opindex fpermitted-flt-eval-methods
 @opindex fpermitted-flt-eval-methods=c11
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index c3001c6ded9..d0a366f1908 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -6249,7 +6249,7 @@ The default is @code{NULL_TREE} which means to not vectorize scatter
 stores.
 @end deftypefn
 
-@deftypefn {Target Hook} int TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN (struct cgraph_node *@var{}, struct cgraph_simd_clone *@var{}, @var{tree}, @var{int})
+@deftypefn {Target Hook} int TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN (struct cgraph_node *@var{}, struct cgraph_simd_clone *@var{}, @var{tree}, @var{int}, @var{bool})
 This hook should set @var{vecsize_mangle}, @var{vecsize_int}, @var{vecsize_float}
 fields in @var{simd_clone} structure pointed by @var{clone_info} argument and also
 @var{simdlen} field if it was previously 0.
diff --git a/gcc/omp-simd-clone.cc b/gcc/omp-simd-clone.cc
index 34cbee5afcd..f9e98b099d1 100644
--- a/gcc/omp-simd-clone.cc
+++ b/gcc/omp-simd-clone.cc
@@ -51,6 +51,152 @@ along with GCC; see the file COPYING3.  If not see
 #include "stringpool.h"
 #include "attribs.h"
 #include "omp-simd-clone.h"
+#include "omp-low.h"
+#include "omp-general.h"
+
+/* Helper function for mark_auto_simd_clone; return false if the statement
+   violates restrictions for an "omp declare simd" function.  Specifically,
+   the function must not
+   - throw or call setjmp/longjmp
+   - write memory that could alias parallel calls
+   - include openmp directives or calls
+   - call functions that might do those things */
+
+static bool
+auto_simd_check_stmt (gimple *stmt, tree outer)
+{
+  tree decl;
+
+  switch (gimple_code (stmt))
+    {
+    case GIMPLE_CALL:
+      decl = gimple_call_fndecl (stmt);
+
+      /* We can't know whether indirect calls are safe.  */
+      if (decl == NULL_TREE)
+	return false;
+
+      /* Calls to functions that are CONST or PURE are ok.  */
+      if (gimple_call_flags (stmt) & (ECF_CONST | ECF_PURE))
+	break;
+
+      /* Calls to functions that are already marked "omp declare simd" are
+	 OK.  */
+      if (lookup_attribute ("omp declare simd", DECL_ATTRIBUTES (decl)))
+	break;
+
+      /* Let recursive calls to the current function through.  */
+      if (decl == outer)
+	break;
+
+      /* Other function calls are not permitted.  */
+      return false;
+
+      /* OpenMP directives are not permitted.  */
+    CASE_GIMPLE_OMP:
+      return false;
+
+      /* Conservatively reject all EH-related constructs.  */
+    case GIMPLE_CATCH:
+    case GIMPLE_EH_FILTER:
+    case GIMPLE_EH_MUST_NOT_THROW:
+    case GIMPLE_EH_ELSE:
+    case GIMPLE_EH_DISPATCH:
+    case GIMPLE_RESX:
+    case GIMPLE_TRY:
+      return false;
+
+      /* Asms are not permitted since we don't know what they do.  */
+    case GIMPLE_ASM:
+      return false;
+
+    default:
+      break;
+    }
+
+  /* Memory writes are not permitted.
+     FIXME: this could be relaxed a little to permit writes to
+     function-local variables that could not alias other instances
+     of the function running in parallel.  */
+  if (gimple_store_p (stmt))
+    return false;
+  else
+    return true;
+}
+
+/* If the function NODE appears suitable for auto-annotation with "declare
+   simd", add and return such an attribute, otherwise return null.  */
+
+static tree
+mark_auto_simd_clone (struct cgraph_node *node)
+{
+  tree decl = node->decl;
+  tree t;
+  machine_mode m;
+  tree result;
+  basic_block bb;
+
+  /* Nothing to do if the function isn't a definition or doesn't
+     have a body.  */
+  if (!node->definition || !node->has_gimple_body_p ())
+    return NULL_TREE;
+
+  /* Nothing to do if the function already has the "omp declare simd"
+     attribute, is marked noclone, or is not "omp declare target".  */
+  if (lookup_attribute ("omp declare simd", DECL_ATTRIBUTES (decl))
+      || lookup_attribute ("noclone", DECL_ATTRIBUTES (decl))
+      || !lookup_attribute ("omp declare target", DECL_ATTRIBUTES (decl)))
+    return NULL_TREE;
+
+  /* Backends will check for vectorizable arguments/return types in a
+     target-specific way, but we can immediately filter out functions
+     that have non-scalar arguments/return types.  Also, atomic types
+     trigger warnings in simd_clone_clauses_extract.  */
+  t = TREE_TYPE (TREE_TYPE (decl));
+  m = TYPE_MODE (t);
+  if (!(VOID_TYPE_P (t) || is_a <scalar_mode> (m)) || TYPE_ATOMIC (t))
+    return NULL_TREE;
+
+  if (TYPE_ARG_TYPES (TREE_TYPE (decl)))
+    {
+      for (tree temp = TYPE_ARG_TYPES (TREE_TYPE (decl));
+	   temp; temp = TREE_CHAIN (temp))
+	{
+	  t = TREE_VALUE (temp);
+	  m = TYPE_MODE (t);
+	  if (!(VOID_TYPE_P (t) || is_a <scalar_mode> (m)) || TYPE_ATOMIC (t))
+	    return NULL_TREE;
+	}
+    }
+  else
+    {
+      for (tree temp = DECL_ARGUMENTS (decl); temp; temp = DECL_CHAIN (temp))
+	{
+	  t = TREE_TYPE (temp);
+	  m = TYPE_MODE (t);
+	  if (!(VOID_TYPE_P (t) || is_a <scalar_mode> (m)) || TYPE_ATOMIC (t))
+	    return NULL_TREE;
+	}
+    }
+
+  /* Scan the function body to see if it is suitable for SIMD-ization.  */
+  node->get_body ();
+
+  FOR_EACH_BB_FN (bb, DECL_STRUCT_FUNCTION (decl))
+    {
+      for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
+	   gsi_next (&gsi))
+	if (!auto_simd_check_stmt (gsi_stmt (gsi), decl))
+	  return NULL_TREE;
+    }
+
+  /* All is good.  */
+  result = tree_cons (get_identifier ("omp declare simd"), NULL,
+		      DECL_ATTRIBUTES (decl));
+  DECL_ATTRIBUTES (decl) = result;
+  return result;
+}
+
 
 /* Return the number of elements in vector type VECTYPE, which is associated
    with a SIMD clone.  At present these always have a constant length.  */
@@ -430,10 +576,12 @@ simd_clone_mangle (struct cgraph_node *node,
   return get_identifier (str);
 }
 
-/* Create a simd clone of OLD_NODE and return it.  */
+/* Create a simd clone of OLD_NODE and return it.  If FORCE_LOCAL is true,
+   create it as a local symbol, otherwise copy the symbol linkage and
+   visibility attributes from OLD_NODE.  */
 
 static struct cgraph_node *
-simd_clone_create (struct cgraph_node *old_node)
+simd_clone_create (struct cgraph_node *old_node, bool force_local)
 {
   struct cgraph_node *new_node;
   if (old_node->definition)
@@ -463,23 +611,38 @@ simd_clone_create (struct cgraph_node *old_node)
     return new_node;
 
   set_decl_built_in_function (new_node->decl, NOT_BUILT_IN, 0);
-  TREE_PUBLIC (new_node->decl) = TREE_PUBLIC (old_node->decl);
-  DECL_COMDAT (new_node->decl) = DECL_COMDAT (old_node->decl);
-  DECL_WEAK (new_node->decl) = DECL_WEAK (old_node->decl);
-  DECL_EXTERNAL (new_node->decl) = DECL_EXTERNAL (old_node->decl);
-  DECL_VISIBILITY_SPECIFIED (new_node->decl)
-    = DECL_VISIBILITY_SPECIFIED (old_node->decl);
-  DECL_VISIBILITY (new_node->decl) = DECL_VISIBILITY (old_node->decl);
-  DECL_DLLIMPORT_P (new_node->decl) = DECL_DLLIMPORT_P (old_node->decl);
-  if (DECL_ONE_ONLY (old_node->decl))
-    make_decl_one_only (new_node->decl, DECL_ASSEMBLER_NAME (new_node->decl));
-
-  /* The method cgraph_version_clone_with_body () will force the new
-     symbol local.  Undo this, and inherit external visibility from
-     the old node.  */
-  new_node->local = old_node->local;
-  new_node->externally_visible = old_node->externally_visible;
-  new_node->calls_declare_variant_alt = old_node->calls_declare_variant_alt;
+  if (force_local)
+    {
+      TREE_PUBLIC (new_node->decl) = 0;
+      DECL_COMDAT (new_node->decl) = 0;
+      DECL_WEAK (new_node->decl) = 0;
+      DECL_EXTERNAL (new_node->decl) = 0;
+      DECL_VISIBILITY_SPECIFIED (new_node->decl) = 0;
+      DECL_VISIBILITY (new_node->decl) = VISIBILITY_DEFAULT;
+      DECL_DLLIMPORT_P (new_node->decl) = 0;
+    }
+  else
+    {
+      TREE_PUBLIC (new_node->decl) = TREE_PUBLIC (old_node->decl);
+      DECL_COMDAT (new_node->decl) = DECL_COMDAT (old_node->decl);
+      DECL_WEAK (new_node->decl) = DECL_WEAK (old_node->decl);
+      DECL_EXTERNAL (new_node->decl) = DECL_EXTERNAL (old_node->decl);
+      DECL_VISIBILITY_SPECIFIED (new_node->decl)
+	= DECL_VISIBILITY_SPECIFIED (old_node->decl);
+      DECL_VISIBILITY (new_node->decl) = DECL_VISIBILITY (old_node->decl);
+      DECL_DLLIMPORT_P (new_node->decl) = DECL_DLLIMPORT_P (old_node->decl);
+      if (DECL_ONE_ONLY (old_node->decl))
+	make_decl_one_only (new_node->decl,
+			    DECL_ASSEMBLER_NAME (new_node->decl));
+
+      /* The method cgraph_version_clone_with_body () will force the new
+	 symbol local.  Undo this, and inherit external visibility from
+	 the old node.  */
+      new_node->local = old_node->local;
+      new_node->externally_visible = old_node->externally_visible;
+      new_node->calls_declare_variant_alt
+	= old_node->calls_declare_variant_alt;
+    }
 
   return new_node;
 }
@@ -1683,13 +1846,32 @@ simd_clone_adjust (struct cgraph_node *node)
 void
 expand_simd_clones (struct cgraph_node *node)
 {
-  tree attr = lookup_attribute ("omp declare simd",
-				DECL_ATTRIBUTES (node->decl));
-  if (attr == NULL_TREE
-      || node->inlined_to
+  tree attr;
+  bool explicit_p = true;
+
+  if (node->inlined_to
       || lookup_attribute ("noclone", DECL_ATTRIBUTES (node->decl)))
     return;
 
+  attr = lookup_attribute ("omp declare simd",
+			   DECL_ATTRIBUTES (node->decl));
+
+  /* See if we can add an "omp declare simd" directive implicitly
+     before giving up.  */
+  /* FIXME: OpenACC "#pragma acc routine" translates into
+     "omp declare target", but appears also to have some other effects
+     that conflict with generating SIMD clones, causing ICEs.  So don't
+     do this if we've got OpenACC instead of OpenMP.  */
+  if (attr == NULL_TREE
+      && flag_openmp_target_simd_clone
+      && !oacc_get_fn_attrib (node->decl))
+    {
+      attr = mark_auto_simd_clone (node);
+      explicit_p = false;
+    }
+  if (attr == NULL_TREE)
+    return;
+
   /* Ignore
      #pragma omp declare simd
      extern int foo ();
@@ -1714,13 +1896,15 @@ expand_simd_clones (struct cgraph_node *node)
 
       poly_uint64 orig_simdlen = clone_info->simdlen;
       tree base_type = simd_clone_compute_base_data_type (node, clone_info);
+
       /* The target can return 0 (no simd clones should be created),
 	 1 (just one ISA of simd clones should be created) or higher
 	 count of ISA variants.  In that case, clone_info is initialized
 	 for the first ISA variant.  */
       int count
 	= targetm.simd_clone.compute_vecsize_and_simdlen (node, clone_info,
-							  base_type, 0);
+							  base_type, 0,
+							  explicit_p);
       if (count == 0)
 	continue;
 
@@ -1745,7 +1929,8 @@ expand_simd_clones (struct cgraph_node *node)
 	      /* And call the target hook again to get the right ISA.  */
 	      targetm.simd_clone.compute_vecsize_and_simdlen (node, clone,
 							      base_type,
-							      i / 2);
+							      i / 2,
+							      explicit_p);
 	      if ((i & 1) != 0)
 		clone->inbranch = 1;
 	    }
@@ -1763,7 +1948,7 @@ expand_simd_clones (struct cgraph_node *node)
 	  /* Only when we are sure we want to create the clone actually
 	     clone the function (or definitions) or create another
 	     extern FUNCTION_DECL (for prototypes without definitions).  */
-	  struct cgraph_node *n = simd_clone_create (node);
+	  struct cgraph_node *n = simd_clone_create (node, !explicit_p);
 	  if (n == NULL)
 	    {
 	      if (i == 0)
diff --git a/gcc/opts.cc b/gcc/opts.cc
index 54e57f36755..b8ca6fdca82 100644
--- a/gcc/opts.cc
+++ b/gcc/opts.cc
@@ -658,6 +658,7 @@ static const struct default_options default_options_table[] =
       REORDER_BLOCKS_ALGORITHM_STC },
     { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_ftree_loop_vectorize, NULL, 1 },
     { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_ftree_slp_vectorize, NULL, 1 },
+    { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_fopenmp_target_simd_clone, NULL, 1 },
 #ifdef INSN_SCHEDULING
   /* Only run the pre-regalloc scheduling pass if optimizing for speed.  */
     { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_fschedule_insns, NULL, 1 },
diff --git a/gcc/target.def b/gcc/target.def
index 4d49ffc2c88..6e830bed52a 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -1634,7 +1634,7 @@ fields in @var{simd_clone} structure pointed by @var{clone_info} argument and al
 not determined by the bitsize (in which case @var{simdlen} is always used).\n\
 The hook should return 0 if SIMD clones shouldn't be emitted,\n\
 or number of @var{vecsize_mangle} variants that should be emitted.",
-int, (struct cgraph_node *, struct cgraph_simd_clone *, tree, int), NULL)
+int, (struct cgraph_node *, struct cgraph_simd_clone *, tree, int, bool), NULL)
 
 DEFHOOK
 (adjust,
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
new file mode 100644
index 00000000000..ab027a60970
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
@@ -0,0 +1,18 @@
+/* { dg-options "-fopenmp -O2" } */
+
+/* Test that simd clones are generated for functions with "declare target".  */
+
+#pragma omp declare target
+int addit(int a, int b, int c)
+{
+  return a + b;
+}
+#pragma omp end declare target
+
+/* Although addit has external linkage, we expect clones to be generated as
+   for a function with internal linkage.  */
+
+/* { dg-final { scan-assembler "\\.type.*_ZGVbN4vvv_addit,.*function" { target i?86-*-* x86_64-*-* } } } */
+/* { dg-final { scan-assembler "\\.type.*_ZGVbM4vvv_addit,.*function" { target i?86-*-* x86_64-*-* } } } */
+/* { dg-final { scan-assembler-not "\\.globl.*_ZGVbN4vvv_addit" { target i?86-*-* x86_64-*-* } } } */
+/* { dg-final { scan-assembler-not "\\.globl.*_ZGVbM4vvv_addit" { target i?86-*-* x86_64-*-* } } } */
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-2.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-2.c
new file mode 100644
index 00000000000..0ccbfe1d765
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-2.c
@@ -0,0 +1,18 @@
+/* { dg-options "-fopenmp -O2" } */
+
+/* Test that simd clones are not generated for functions with 
+   "declare target" but unsuitable arguments.  */
+
+struct s {
+  int a;
+  int b;
+};
+  
+#pragma omp declare target
+int addit (struct s x)
+{
+  return x.a + x.b;
+}
+#pragma omp end declare target
+
+/* { dg-final { scan-assembler-not "_Z.*_addit" { target i?86-*-* x86_64-*-* } } } */
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-3.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-3.c
new file mode 100644
index 00000000000..c313cfe53b0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-3.c
@@ -0,0 +1,17 @@
+/* { dg-options "-fopenmp -O2" } */
+
+/* Test that simd clones are not generated for functions with 
+   "declare target" but that call possibly side-effecting functions 
+   in the body.  */
+
+extern int f (int);
+
+#pragma omp declare target
+int addit(int a, int b, int c)
+{
+  return f(a) + b;
+}
+#pragma omp end declare target
+
+/* { dg-final { scan-assembler-not "_Z.*_addit" { target i?86-*-* x86_64-*-* } } } */
+
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-4.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-4.c
new file mode 100644
index 00000000000..e32b22f6a59
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-4.c
@@ -0,0 +1,16 @@
+/* { dg-options "-fopenmp -O2" } */
+
+/* Test that simd clones are not generated for functions with 
+   "declare target" but that write memory in the body.  */
+
+extern int save;
+
+#pragma omp declare target
+int addit(int a, int b, int c)
+{
+  save = c;
+  return a + b;
+}
+#pragma omp end declare target
+
+/* { dg-final { scan-assembler-not "_Z.*_addit" { target i?86-*-* x86_64-*-* } } } */
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-5.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-5.c
new file mode 100644
index 00000000000..d39a9ab737f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-5.c
@@ -0,0 +1,13 @@
+/* { dg-options "-fopenmp -Os" } */
+
+/* Test that simd clones are not generated for functions with 
+   "declare target" at -Os.  */
+
+#pragma omp declare target
+int addit(int a, int b, int c)
+{
+  return a + b;
+}
+#pragma omp end declare target
+
+/* { dg-final { scan-assembler-not "_Z.*_addit" { target i?86-*-* x86_64-*-* } } } */
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-6.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-6.c
new file mode 100644
index 00000000000..a0c529b1c4e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-6.c
@@ -0,0 +1,13 @@
+/* { dg-options "-fopenmp -Og" } */
+
+/* Test that simd clones are not generated for functions with 
+   "declare target" at -Og.  */
+
+#pragma omp declare target
+int addit(int a, int b, int c)
+{
+  return a + b;
+}
+#pragma omp end declare target
+
+/* { dg-final { scan-assembler-not "_Z.*_addit" { target i?86-*-* x86_64-*-* } } } */
-- 
2.31.1