[gcc r13-4983] OpenMP: GC unused SIMD clones

[gcc r13-4983] OpenMP: GC unused SIMD clones

[Sandra Loosemore]

https://gcc.gnu.org/g:0425ae780fb2b055d985b5719af5edfaaad5e980

commit r13-4983-g0425ae780fb2b055d985b5719af5edfaaad5e980
Author: Sandra Loosemore <sandra@codesourcery.com>
Date:   Tue Jan 3 17:46:02 2023 +0000

    OpenMP: GC unused SIMD clones
    
    SIMD clones are created during the IPA phase when it is not known whether
    or not the vectorizer can use them.  Clones for functions with external
    linkage are part of the ABI, but local clones can be GC'ed if no calls are
    found in the compilation unit after vectorization.
    
    gcc/ChangeLog
            * cgraph.h (struct cgraph_node): Add gc_candidate bit, modify
            default constructor to initialize it.
            * cgraphunit.cc (expand_all_functions): Save gc_candidate functions
            for last and iterate to handle recursive calls.  Delete leftover
            candidates at the end.
            * omp-simd-clone.cc (simd_clone_create): Set gc_candidate bit
            on local clones.
            * tree-vect-stmts.cc (vectorizable_simd_clone_call): Clear
            gc_candidate bit when a clone is used.
    
    gcc/testsuite/ChangeLog
            * g++.dg/gomp/target-simd-clone-1.C: Tweak to test
            that the unused clone is GC'ed.
            * gcc.dg/gomp/target-simd-clone-1.c: Likewise.

Diff:
---
 gcc/cgraph.h                                    |  7 +++-
 gcc/cgraphunit.cc                               | 49 +++++++++++++++++++++----
 gcc/omp-simd-clone.cc                           |  5 +++
 gcc/testsuite/g++.dg/gomp/target-simd-clone-1.C |  7 +++-
 gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c |  6 ++-
 gcc/tree-vect-stmts.cc                          |  3 ++
 6 files changed, 66 insertions(+), 11 deletions(-)

diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index 8dee2f6e591..5d3ced1b5d5 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -891,7 +891,8 @@ struct GTY((tag ("SYMTAB_FUNCTION"))) cgraph_node : public symtab_node
       versionable (false), can_change_signature (false),
       redefined_extern_inline (false), tm_may_enter_irr (false),
       ipcp_clone (false), declare_variant_alt (false),
-      calls_declare_variant_alt (false), m_uid (uid), m_summary_id (-1)
+      calls_declare_variant_alt (false), gc_candidate (false),
+      m_uid (uid), m_summary_id (-1)
   {}
 
   /* Remove the node from cgraph and all inline clones inlined into it.
@@ -1490,6 +1491,10 @@ struct GTY((tag ("SYMTAB_FUNCTION"))) cgraph_node : public symtab_node
   unsigned declare_variant_alt : 1;
   /* True if the function calls declare_variant_alt functions.  */
   unsigned calls_declare_variant_alt : 1;
+  /* True if the function should only be emitted if it is used.  This flag
+     is set for local SIMD clones when they are created and cleared if the
+     vectorizer uses them.  */
+  unsigned gc_candidate : 1;
 
 private:
   /* Unique id of the node.  */
diff --git a/gcc/cgraphunit.cc b/gcc/cgraphunit.cc
index 548bb853a18..59ce2708b7b 100644
--- a/gcc/cgraphunit.cc
+++ b/gcc/cgraphunit.cc
@@ -1996,19 +1996,52 @@ expand_all_functions (void)
 
   /* Output functions in RPO so callees get optimized before callers.  This
      makes ipa-ra and other propagators to work.
-     FIXME: This is far from optimal code layout.  */
-  for (i = new_order_pos - 1; i >= 0; i--)
-    {
-      node = order[i];
+     FIXME: This is far from optimal code layout.
+     Make multiple passes over the list to defer processing of gc
+     candidates until all potential uses are seen.  */
+  int gc_candidates = 0;
+  int prev_gc_candidates = 0;
 
-      if (node->process)
+  while (1)
+    {
+      for (i = new_order_pos - 1; i >= 0; i--)
 	{
-	  expanded_func_count++;
-	  node->process = 0;
-	  node->expand ();
+	  node = order[i];
+
+	  if (node->gc_candidate)
+	    gc_candidates++;
+	  else if (node->process)
+	    {
+	      expanded_func_count++;
+	      node->process = 0;
+	      node->expand ();
+	    }
 	}
+      if (!gc_candidates || gc_candidates == prev_gc_candidates)
+	break;
+      prev_gc_candidates = gc_candidates;
+      gc_candidates = 0;
     }
 
+  /* Free any unused gc_candidate functions.  */
+  if (gc_candidates)
+    for (i = new_order_pos - 1; i >= 0; i--)
+      {
+	node = order[i];
+	if (node->gc_candidate)
+	  {
+	    struct function *fn = DECL_STRUCT_FUNCTION (node->decl);
+	    if (symtab->dump_file)
+	      fprintf (symtab->dump_file,
+		       "Deleting unused function %s\n",
+		       IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)));
+	    node->process = false;
+	    free_dominance_info (fn, CDI_DOMINATORS);
+	    free_dominance_info (fn, CDI_POST_DOMINATORS);
+	    node->release_body (false);
+	  }
+      }
+
   if (dump_file)
     fprintf (dump_file, "Expanded functions with time profile (%s):%u/%u\n",
 	     main_input_filename, profiled_func_count, expanded_func_count);
diff --git a/gcc/omp-simd-clone.cc b/gcc/omp-simd-clone.cc
index b0fd2d2ddc5..92b629b1021 100644
--- a/gcc/omp-simd-clone.cc
+++ b/gcc/omp-simd-clone.cc
@@ -702,6 +702,11 @@ simd_clone_create (struct cgraph_node *old_node, bool force_local)
 	= old_node->calls_declare_variant_alt;
     }
 
+  /* Mark clones with internal linkage as gc'able, so they will not be
+     emitted unless the vectorizer can actually use them.  */
+  if (!TREE_PUBLIC (new_node->decl))
+    new_node->gc_candidate = true;
+
   return new_node;
 }
 
diff --git a/gcc/testsuite/g++.dg/gomp/target-simd-clone-1.C b/gcc/testsuite/g++.dg/gomp/target-simd-clone-1.C
index 10b5ac38812..b96473642bb 100644
--- a/gcc/testsuite/g++.dg/gomp/target-simd-clone-1.C
+++ b/gcc/testsuite/g++.dg/gomp/target-simd-clone-1.C
@@ -1,5 +1,5 @@
 /* { dg-options "-fopenmp -O2" } */
-/* { dg-additional-options "-fopenmp-target-simd-clone=any -fdump-ipa-simdclone-details" } */
+/* { dg-additional-options "-fopenmp-target-simd-clone=any -fdump-ipa-simdclone-details -fdump-ipa-cgraph" } */
 
 /* Test that simd clones are generated for functions with "declare target".  */
 
@@ -23,3 +23,8 @@ void callit (int *a, int *b, int *c)
 
 /* { dg-final { scan-ipa-dump "Generated local clone _ZGV.*N.*__Z5additii" "simdclone" { target x86_64-*-* } } } */
 /* { dg-final { scan-ipa-dump "Generated local clone _ZGV.*M.*__Z5additii" "simdclone" { target x86_64-*-* } } } */
+
+/* Only the "N" clone is used.  The other one should be GC'ed.  */
+
+/* { dg-final { scan-ipa-dump "Deleting unused function _ZGV.*M.*__Z5additii" "cgraph" { target x86_64-*-* } } } */
+
diff --git a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
index 388dc2a956c..0d74aa971f9 100644
--- a/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
+++ b/gcc/testsuite/gcc.dg/gomp/target-simd-clone-1.c
@@ -1,5 +1,5 @@
 /* { dg-options "-fopenmp -O2" } */
-/* { dg-additional-options "-fopenmp-target-simd-clone=any -fdump-ipa-simdclone-details" } */
+/* { dg-additional-options "-fopenmp-target-simd-clone=any -fdump-ipa-simdclone-details -fdump-ipa-cgraph" } */
 
 /* Test that simd clones are generated for functions with "declare target".  */
 
@@ -23,3 +23,7 @@ void callit (int *a, int *b, int *c)
 
 /* { dg-final { scan-ipa-dump "Generated local clone _ZGV.*N.*_addit" "simdclone" { target x86_64-*-* } } } */
 /* { dg-final { scan-ipa-dump "Generated local clone _ZGV.*M.*_addit" "simdclone" { target x86_64-*-* } } } */
+
+/* Only the "N" clone is used.  The other one should be GC'ed.  */
+
+/* { dg-final { scan-ipa-dump "Deleting unused function _ZGV.*M.*_addit" "cgraph" { target x86_64-*-* } } } */
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index fb367518396..6ddd41fb473 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -4620,6 +4620,9 @@ vectorizable_simd_clone_call (vec_info *vinfo, stmt_vec_info stmt_info,
     }
   vargs.release ();
 
+  /* Mark the clone as no longer being a candidate for GC.  */
+  bestn->gc_candidate = false;
+
   /* The call in STMT might prevent it from being removed in dce.
      We however cannot remove it here, due to the way the ssa name
      it defines is mapped to the new definition.  So just replace