From: Sergei Trofimovich <siarheit@google.com>
Date: Mon, 11 Jan 2021 18:05:57 +0000 (+0000)
Subject: tree-optimization/98499 - fix modref analysis on RVO statements
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=11056ab7687f7156846e93557c9171b77713bd7e;p=gcc.git

tree-optimization/98499 - fix modref analysis on RVO statements

Before the change RVO gimple statements were treated as local
stores by modres analysis. But in practice RVO escapes target.

2021-02-01  Sergei Trofimovich  <siarheit@google.com>

gcc/ChangeLog:

	PR tree-optimization/98499
	* ipa-modref.c (analyze_ssa_name_flags): treat RVO
	conservatively and assume all possible side-effects.

gcc/testsuite/ChangeLog:

	PR tree-optimization/98499
	* g++.dg/pr98499.C: new test.
---

diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
index 8a5669c7f9b..7aaf53be8f4 100644
--- a/gcc/ipa-modref.c
+++ b/gcc/ipa-modref.c
@@ -36,7 +36,7 @@ along with GCC; see the file COPYING3.  If not see
 
    The following information is computed
      1) load/store access tree described in ipa-modref-tree.h
-	This is used by tree-ssa-alias to disambiguate load/dtores
+	This is used by tree-ssa-alias to disambiguate load/stores
      2) EAF flags used by points-to analysis (in tree-ssa-structlias).
 	and defined in tree-core.h.
    and stored to optimization_summaries.
@@ -1604,7 +1604,7 @@ analyze_ssa_name_flags (tree name, vec<modref_lattice> &lattice, int depth,
 	continue;
       if (dump_file)
 	{
-	  fprintf (dump_file, "%*s  Analyzing stmt:", depth * 4, "");
+	  fprintf (dump_file, "%*s  Analyzing stmt: ", depth * 4, "");
 	  print_gimple_stmt (dump_file, use_stmt, 0);
 	}
 
@@ -1621,9 +1621,19 @@ analyze_ssa_name_flags (tree name, vec<modref_lattice> &lattice, int depth,
       else if (gcall *call = dyn_cast <gcall *> (use_stmt))
 	{
 	  tree callee = gimple_call_fndecl (call);
-
+	  /* Return slot optiomization would require bit of propagation;
+	     give up for now.  */
+	  if (gimple_call_return_slot_opt_p (call)
+	      && gimple_call_lhs (call) != NULL_TREE
+	      && TREE_ADDRESSABLE (TREE_TYPE (gimple_call_lhs (call))))
+	    {
+	      if (dump_file)
+		fprintf (dump_file, "%*s  Unhandled return slot opt\n",
+			 depth * 4, "");
+	      lattice[index].merge (0);
+	    }
 	  /* Recursion would require bit of propagation; give up for now.  */
-	  if (callee && !ipa && recursive_call_p (current_function_decl,
+	  else if (callee && !ipa && recursive_call_p (current_function_decl,
 						  callee))
 	    lattice[index].merge (0);
 	  else
diff --git a/gcc/testsuite/g++.dg/pr98499.C b/gcc/testsuite/g++.dg/pr98499.C
new file mode 100644
index 00000000000..ace088aeed9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr98499.C
@@ -0,0 +1,31 @@
+/* PR tree-optimization/98499.  */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+struct string {
+  // pointer to local store
+  char * _M_buf;
+  // local store
+  char _M_local_buf[16];
+
+  __attribute__((noinline)) string() : _M_buf(_M_local_buf) {}
+
+  ~string() {
+    if (_M_buf != _M_local_buf)
+      __builtin_trap();
+  }
+
+  string(const string &__str); // no copies
+};
+
+__attribute__((noinline)) static string dir_name() { return string(); }
+class Importer {
+  string base_path;
+
+public:
+  __attribute__((noinline)) Importer() : base_path (dir_name()) {}
+};
+
+int main() {
+  Importer imp;
+}