re PR c++/70018 (Possible issue around IPO and C++ comdats discovered as pure/const)

	PR ipa/70018
	* cgraph.c (cgraph_set_const_flag_1): Only set as pure if
	function does not bind to current def.
	* ipa-pure-const.c (worse_state): Add FROM and TO parameters;
	handle conservatively calls to functions that does not need to bind
	to current def.
	(check_call): Update call of worse_state.
	(ignore_edge_for_nothrow): Update.
	(ignore_edge_for_pure_const): Likewise.
	(propagate_pure_const): Update calls to worse_state.
	(skip_function_for_local_pure_const): Reformat comments.

	* g++.dg/ipa/pure-const-1.C: New testcase.
	* g++.dg/ipa/pure-const-2.C: New testcase.
	* g++.dg/ipa/pure-const-3.C: New testcase.

From-SVN: r235065

1 files changed, 29 insertions, 1 deletions

diff --git a/gcc/cgraph.c b/gcc/cgraph.c
index 0ced2db..c43adb9 100644
--- a/gcc/cgraph.c
+++ b/gcc/cgraph.c
@@ -2393,7 +2393,35 @@ cgraph_set_const_flag_1 (cgraph_node *node, void *data)
       if (DECL_STATIC_DESTRUCTOR (node->decl))
 	DECL_STATIC_DESTRUCTOR (node->decl) = 0;
     }
-  TREE_READONLY (node->decl) = data != NULL;
+
+  /* Consider function:
+
+     bool a(int *p)
+     {
+       return *p==*p;
+     }
+
+     During early optimization we will turn this into:
+
+     bool a(int *p)
+     {
+       return true;
+     }
+
+     Now if this function will be detected as CONST however when interposed it
+     may end up being just pure.  We always must assume the worst scenario here.
+   */
+  if (TREE_READONLY (node->decl))
+    ;
+  else if (node->binds_to_current_def_p ())
+    TREE_READONLY (node->decl) = data != NULL;
+  else
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "Dropping state to PURE because function does "
+		 "not bind to current def.\n");
+      DECL_PURE_P (node->decl) = data != NULL;
+    }
   DECL_LOOPING_CONST_OR_PURE_P (node->decl) = ((size_t)data & 2) != 0;
   return false;
 }