Re: [PATCH] Allow new/delete operator deletion only for replaceable.

["Martin Liška" <mliska@suse.cz>]

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On 4/10/20 10:18 AM, Jonathan Wakely wrote:
> On Fri, 10 Apr 2020 at 09:08, Martin Liška <mliska@suse.cz> wrote:
>> Marc pointed out that some targets do not use the leading '_' (or use 2 dashes?) for mangled named?
> 
> Double underscore at the start. I think darwin uses that.
> 

Ah yeah, not dashes, but underscores ;)
It's fixed in attached patch that I've been testing right now.

Martin

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From 4043b187ee8e6d7d0c05a6463e38ca54ba4acf75 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Thu, 9 Apr 2020 15:50:58 +0200
Subject: [PATCH] List valid pairs for new and delete operators.

gcc/ChangeLog:

2020-04-09  Martin Liska  <mliska@suse.cz>

	PR c++/94314
	* cgraphclones.c (set_new_clone_decl_and_node_flags): Drop
	DECL_IS_REPLACEABLE_OPERATOR during cloning.
	* tree-ssa-dce.c (valid_new_delete_pair_p): New function.
	(propagate_necessity): Check operator names.
	(perform_tree_ssa_dce): Delete valid_pairs.

gcc/testsuite/ChangeLog:

2020-04-09  Martin Liska  <mliska@suse.cz>

	PR c++/94314
	* g++.dg/pr94314-4.C: New test.
---
 gcc/cgraphclones.c               |  2 +
 gcc/testsuite/g++.dg/pr94314-4.C | 33 +++++++++++
 gcc/tree-ssa-dce.c               | 99 ++++++++++++++++++++++++++++----
 3 files changed, 124 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/pr94314-4.C

diff --git a/gcc/cgraphclones.c b/gcc/cgraphclones.c
index c73b8f810f0..8f541a28b6e 100644
--- a/gcc/cgraphclones.c
+++ b/gcc/cgraphclones.c
@@ -165,6 +165,7 @@ set_new_clone_decl_and_node_flags (cgraph_node *new_node)
   DECL_STATIC_DESTRUCTOR (new_node->decl) = 0;
   DECL_SET_IS_OPERATOR_NEW (new_node->decl, 0);
   DECL_SET_IS_OPERATOR_DELETE (new_node->decl, 0);
+  DECL_IS_REPLACEABLE_OPERATOR (new_node->decl) = 0;
 
   new_node->externally_visible = 0;
   new_node->local = 1;
@@ -1030,6 +1031,7 @@ cgraph_node::create_version_clone_with_body
   DECL_STATIC_DESTRUCTOR (new_decl) = 0;
   DECL_SET_IS_OPERATOR_NEW (new_decl, 0);
   DECL_SET_IS_OPERATOR_DELETE (new_decl, 0);
+  DECL_IS_REPLACEABLE_OPERATOR (new_decl) = 0;
 
   /* Create the new version's call-graph node.
      and update the edges of the new node. */
diff --git a/gcc/testsuite/g++.dg/pr94314-4.C b/gcc/testsuite/g++.dg/pr94314-4.C
new file mode 100644
index 00000000000..afa2a443dc4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr94314-4.C
@@ -0,0 +1,33 @@
+/* PR c++/94314.  */
+/* { dg-do run } */
+/* { dg-options "-O2 -fdump-tree-cddce-details -std=c++14" } */
+/* { dg-additional-options "-fdelete-null-pointer-checks" } */
+
+#include <stdio.h>
+
+int count = 0;
+
+__attribute__((malloc, noinline)) void* operator new[](__SIZE_TYPE__ sz) {
+  ++count;
+  return ::operator new(sz);
+}
+
+void operator delete[](void* ptr) noexcept {
+  --count;
+  ::operator delete(ptr);
+}
+
+void operator delete[](void* ptr, __SIZE_TYPE__ sz) noexcept {
+  --count;
+  ::operator delete(ptr, sz);
+}
+
+int main() {
+  delete[] new int[1];
+  if (count != 0)
+    __builtin_abort ();
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-not "Deleting : operator delete" "cddce1"} } */
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index fd5f24c746c..f66069e410d 100644
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -646,6 +646,76 @@ degenerate_phi_p (gimple *phi)
   return true;
 }
 
+/* Valid pairs of new and delete operators for DCE.  */
+static hash_set<nofree_string_hash> *valid_pairs = NULL;
+
+/* Return that NEW_CALL and DELETE_CALL are a valid pair of new
+   and delete  operators.  */
+
+static bool
+valid_new_delete_pair_p (gimple *new_call, gimple *delete_call)
+{
+  const char *new_name
+    = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call)));
+  const char *delete_name
+    = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call)));
+
+  if (new_name[0] == '_' and new_name[1] == '_')
+    ++new_name;
+  if (delete_name[0] == '_' and delete_name[1] == '_')
+    ++delete_name;
+
+  char *needle = concat (new_name, ":", delete_name, NULL);
+
+  if (valid_pairs == NULL)
+    {
+      valid_pairs = new hash_set<nofree_string_hash> ();
+      /* Invalid pairs:
+	 non-[] and []
+	 aligned and non-aligned
+      */
+
+      const char *pairs[] = {
+	  /* non-[] operators.  */
+	  "_Znwm:_ZdlPv" ,
+	  "_Znwm:_ZdlPvm" ,
+	  "_Znwm:_ZdlPvRKSt9nothrow_t" ,
+	  "_ZnwmRKSt9nothrow_t:_ZdlPv" ,
+	  "_ZnwmRKSt9nothrow_t:_ZdlPvm" ,
+	  "_ZnwmRKSt9nothrow_t:_ZdlPvRKSt9nothrow_t" ,
+	  /* non-[] operators with alignment.  */
+	  "_ZnwmSt11align_val_t:_ZdlPvmSt11align_val_t" ,
+	  "_ZnwmSt11align_val_t:_ZdlPvSt11align_val_t" ,
+	  "_ZnwmSt11align_val_t:_ZdlPvSt11align_val_tRKSt9nothrow_t" ,
+	  "_ZnwmSt11align_val_tRKSt9nothrow_t:_ZdlPvmSt11align_val_t" ,
+	  "_ZnwmSt11align_val_tRKSt9nothrow_t:_ZdlPvSt11align_val_t" ,
+	  "_ZnwmSt11align_val_tRKSt9nothrow_t:_ZdlPvSt11align_val_tRKSt9nothrow_t" ,
+	  /* [] operators.  */
+	   "_Znam:_ZdaPv" ,
+	   "_Znam:_ZdaPvm" ,
+	   "_Znam:_ZdaPvRKSt9nothrow_t" ,
+	   "_ZnamRKSt9nothrow_t:_ZdaPv" ,
+	   "_ZnamRKSt9nothrow_t:_ZdaPvm" ,
+	   "_ZnamRKSt9nothrow_t:_ZdaPvRKSt9nothrow_t" ,
+	  /* [] operators with alignment.  */
+	   "_ZnamSt11align_val_t:_ZdaPvmSt11align_val_t" ,
+	   "_ZnamSt11align_val_t:_ZdaPvSt11align_val_t" ,
+	   "_ZnamSt11align_val_t:_ZdaPvSt11align_val_tRKSt9nothrow_t" ,
+	   "_ZnamSt11align_val_tRKSt9nothrow_t:_ZdaPvmSt11align_val_t",
+	   "_ZnamSt11align_val_tRKSt9nothrow_t:_ZdaPvSt11align_val_t",
+	   "_ZnamSt11align_val_tRKSt9nothrow_t:_ZdaPvSt11align_val_tRKSt9nothrow_t",
+	   NULL
+      };
+
+      for (unsigned i = 0; pairs[i] != NULL; i++)
+	valid_pairs->add (pairs[i]);
+    }
+
+  bool r = valid_pairs->contains (needle);
+  free (needle);
+  return r;
+}
+
 /* Propagate necessity using the operands of necessary statements.
    Process the uses on each statement in the worklist, and add all
    feeding statements which contribute to the calculation of this
@@ -824,16 +894,23 @@ propagate_necessity (bool aggressive)
 			   || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
 		      || DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee)))
 		{
-		  /* Delete operators can have alignment and (or) size as next
-		     arguments.  When being a SSA_NAME, they must be marked
-		     as necessary.  */
-		  if (is_delete_operator && gimple_call_num_args (stmt) >= 2)
-		    for (unsigned i = 1; i < gimple_call_num_args (stmt); i++)
-		      {
-			tree arg = gimple_call_arg (stmt, i);
-			if (TREE_CODE (arg) == SSA_NAME)
-			  mark_operand_necessary (arg);
-		      }
+		  if (is_delete_operator)
+		    {
+		      if (!valid_new_delete_pair_p (def_stmt, stmt))
+			mark_operand_necessary (gimple_call_arg (stmt, 0));
+
+		      /* Delete operators can have alignment and (or) size
+			 as next arguments.  When being a SSA_NAME, they
+			 must be marked as necessary.  */
+		      if (gimple_call_num_args (stmt) >= 2)
+			for (unsigned i = 1; i < gimple_call_num_args (stmt);
+			     i++)
+			  {
+			    tree arg = gimple_call_arg (stmt, i);
+			    if (TREE_CODE (arg) == SSA_NAME)
+			      mark_operand_necessary (arg);
+			  }
+		    }
 
 		  continue;
 		}
@@ -1662,6 +1739,8 @@ perform_tree_ssa_dce (bool aggressive)
   visited = BITMAP_ALLOC (NULL);
   propagate_necessity (aggressive);
   BITMAP_FREE (visited);
+  delete valid_pairs;
+  valid_pairs = NULL;
 
   something_changed |= eliminate_unnecessary_stmts ();
   something_changed |= cfg_altered;
-- 
2.26.0