openmp: Tune omp_max_vf for offload targets

If requested, return the vectorization factor appropriate for the offload
device, if any.

This change gives a significant speedup in the BabelStream "dot" benchmark on
amdgcn.

The omp_adjust_chunk_size usecase is set "false", for now, but I intend to
change that in a follow-up patch.

Note that NVPTX SIMT offload does not use this code-path.

gcc/ChangeLog:

	* gimple-loop-versioning.cc (loop_versioning::loop_versioning): Set
	omp_max_vf to offload == false.
	* omp-expand.cc (omp_adjust_chunk_size): Likewise.
	* omp-general.cc (omp_max_vf): Add "offload" parameter, and detect
	amdgcn offload devices.
	* omp-general.h (omp_max_vf): Likewise.
	* omp-low.cc (lower_rec_simd_input_clauses): Pass offload state to
	omp_max_vf.

diff --git a/gcc/gimple-loop-versioning.cc b/gcc/gimple-loop-versioning.cc
index 107b00200247bba4139f5c5e217a8b3ab188d942..2968c929d04aeb2f77063f1ac6340e7f109a0c90 100644 (file)
--- a/gcc/gimple-loop-versioning.cc
+++ b/gcc/gimple-loop-versioning.cc
@@ -554,7 +554,7 @@ loop_versioning::loop_versioning (function *fn)
      handled efficiently by scalar code.  omp_max_vf calculates the
      maximum number of bytes in a vector, when such a value is relevant
      to loop optimization.  */
-  m_maximum_scale = estimated_poly_value (omp_max_vf ());
+  m_maximum_scale = estimated_poly_value (omp_max_vf (false));
   m_maximum_scale = MAX (m_maximum_scale, MAX_FIXED_MODE_SIZE);
 }
 

diff --git a/gcc/omp-expand.cc b/gcc/omp-expand.cc
index b0b4ddf5dbc8c2135dd4639f50253f8dfab2afa6..907fd46a5b26ea11079d40a1ca31bd7d102e2256 100644 (file)
--- a/gcc/omp-expand.cc
+++ b/gcc/omp-expand.cc
@@ -212,7 +212,7 @@ omp_adjust_chunk_size (tree chunk_size, bool simd_schedule)
   if (!simd_schedule || integer_zerop (chunk_size))
     return chunk_size;
 
-  poly_uint64 vf = omp_max_vf ();
+  poly_uint64 vf = omp_max_vf (false);
   if (known_eq (vf, 1U))
     return chunk_size;
 

diff --git a/gcc/omp-general.cc b/gcc/omp-general.cc
index f74b9bf5e96c349475da3ebadeb355a0ae92e7c5..1ae575ee181f6fd5b4d18153703f07eae9412c92 100644 (file)
--- a/gcc/omp-general.cc
+++ b/gcc/omp-general.cc
@@ -987,10 +987,11 @@ find_combined_omp_for (tree *tp, int *walk_subtrees, void *data)
   return NULL_TREE;
 }
 
-/* Return maximum possible vectorization factor for the target.  */
+/* Return maximum possible vectorization factor for the target, or for
+   the OpenMP offload target if one exists.  */
 
 poly_uint64
-omp_max_vf (void)
+omp_max_vf (bool offload)
 {
   if (!optimize
       || optimize_debug
@@ -999,6 +1000,18 @@ omp_max_vf (void)
          && OPTION_SET_P (flag_tree_loop_vectorize)))
     return 1;
 
+  if (ENABLE_OFFLOADING && offload)
+    {
+      for (const char *c = getenv ("OFFLOAD_TARGET_NAMES"); c;)
+       {
+         if (startswith (c, "amdgcn"))
+           return ordered_max (64, omp_max_vf (false));
+         else if ((c = strchr (c, ':')))
+           c++;
+       }
+      /* Otherwise, fall through to host VF.  */
+    }
+
   auto_vector_modes modes;
   targetm.vectorize.autovectorize_vector_modes (&modes, true);
   if (!modes.is_empty ())

diff --git a/gcc/omp-general.h b/gcc/omp-general.h
index f37781316269cd38076eb4900fe5d868091a3db9..70f78d2055b7439b14c3109e3bb8adb35cc2ec24 100644 (file)
--- a/gcc/omp-general.h
+++ b/gcc/omp-general.h
@@ -162,7 +162,7 @@ extern void omp_extract_for_data (gomp_for *for_stmt, struct omp_for_data *fd,
                                  struct omp_for_data_loop *loops);
 extern gimple *omp_build_barrier (tree lhs);
 extern tree find_combined_omp_for (tree *, int *, void *);
-extern poly_uint64 omp_max_vf (void);
+extern poly_uint64 omp_max_vf (bool);
 extern int omp_max_simt_vf (void);
 extern const char *omp_context_name_list_prop (tree);
 extern void omp_construct_traits_to_codes (tree, int, enum tree_code *);

diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc
index 44c4310075bfb5cd7ac1959157268d0b0afbe696..70a2c108fbca672fd3da8868bb1a212be2956aae 100644 (file)
--- a/gcc/omp-low.cc
+++ b/gcc/omp-low.cc
@@ -4589,7 +4589,8 @@ lower_rec_simd_input_clauses (tree new_var, omp_context *ctx,
 {
   if (known_eq (sctx->max_vf, 0U))
     {
-      sctx->max_vf = sctx->is_simt ? omp_max_simt_vf () : omp_max_vf ();
+      sctx->max_vf = (sctx->is_simt ? omp_max_simt_vf ()
+                     : omp_max_vf (omp_maybe_offloaded_ctx (ctx)));
       if (maybe_gt (sctx->max_vf, 1U))
        {
          tree c = omp_find_clause (gimple_omp_for_clauses (ctx->stmt),