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[PATCH] Fix devirt from dropping lhs with TREE_ADDRESSABLE type on noreturn calls (PR c++/71210)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jan Hubicka <jh at suse dot cz>, Jason Merrill <jason at redhat dot com>, Richard Biener <rguenther at suse dot de>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 20 May 2016 13:31:22 +0200
- Subject: [PATCH] Fix devirt from dropping lhs with TREE_ADDRESSABLE type on noreturn calls (PR c++/71210)
- Authentication-results: sourceware.org; auth=none
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
Hi!
This is another case in the never ending story of dropping lhs of noreturn
calls when we shouldn't.
Though, in this case, while we can optimize a call to a direct call to
normal [[noreturn]] method, we can also optimize into __cxa_pure_virtual
or __builtin_unreachable. And in those cases IMHO it is desirable to
not have the lhs, but we should also adjust gimple_call_set_fntype,
because we are now calling something different, we've just reused the
same call stmt for that.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-05-20 Jakub Jelinek <jakub@redhat.com>
PR c++/71210
* gimple-fold.c (gimple_fold_call): Do not remove lhs of noreturn
calls if the LHS is variable length or has addressable type.
If targets[0]->decl is a noreturn call with void return type and
zero arguments, adjust fntype and remove lhs in that case.
* g++.dg/opt/pr71210-1.C: New test.
* g++.dg/opt/pr71210-2.C: New test.
--- gcc/gimple-fold.c.jj 2016-05-03 14:12:19.000000000 +0200
+++ gcc/gimple-fold.c 2016-05-20 10:18:22.818728240 +0200
@@ -3039,10 +3039,25 @@ gimple_fold_call (gimple_stmt_iterator *
}
if (targets.length () == 1)
{
- gimple_call_set_fndecl (stmt, targets[0]->decl);
+ tree fndecl = targets[0]->decl;
+ gimple_call_set_fndecl (stmt, fndecl);
changed = true;
+ /* If changing the call to __cxa_pure_virtual
+ or similar noreturn function, adjust gimple_call_fntype
+ too. */
+ if ((gimple_call_flags (stmt) & ECF_NORETURN)
+ && VOID_TYPE_P (TREE_TYPE (TREE_TYPE (fndecl)))
+ && TYPE_ARG_TYPES (TREE_TYPE (fndecl))
+ && (TREE_VALUE (TYPE_ARG_TYPES (TREE_TYPE (fndecl)))
+ == void_type_node))
+ gimple_call_set_fntype (stmt, TREE_TYPE (fndecl));
/* If the call becomes noreturn, remove the lhs. */
- if (lhs && (gimple_call_flags (stmt) & ECF_NORETURN))
+ if (lhs
+ && (gimple_call_flags (stmt) & ECF_NORETURN)
+ && (VOID_TYPE_P (TREE_TYPE (gimple_call_fntype (stmt)))
+ || ((TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (lhs)))
+ == INTEGER_CST)
+ && !TREE_ADDRESSABLE (TREE_TYPE (lhs)))))
{
if (TREE_CODE (lhs) == SSA_NAME)
{
--- gcc/testsuite/g++.dg/opt/pr71210-1.C.jj 2016-05-20 09:30:13.119724805 +0200
+++ gcc/testsuite/g++.dg/opt/pr71210-1.C 2016-05-20 09:29:42.000000000 +0200
@@ -0,0 +1,14 @@
+// PR c++/71210
+// { dg-do compile }
+// { dg-options "-O2" }
+
+#include <typeinfo>
+
+void f1 (const std::type_info&) __attribute__((noreturn));
+struct S1 { ~S1 (); };
+struct S2
+{
+ virtual S1 f2 () const { f1 (typeid (*this)); }
+ S1 f3 () const { return f2 (); }
+};
+void f4 () { S2 a; a.f3 (); }
--- gcc/testsuite/g++.dg/opt/pr71210-2.C.jj 2016-05-20 10:20:00.918402232 +0200
+++ gcc/testsuite/g++.dg/opt/pr71210-2.C 2016-05-20 10:19:48.000000000 +0200
@@ -0,0 +1,23 @@
+// PR c++/71210
+// { dg-do compile }
+// { dg-options "-O2" }
+
+struct C { int a; int b; C (); ~C (); };
+
+namespace
+{
+ struct A
+ {
+ A () {}
+ virtual C bar (int) = 0;
+ C baz (int x) { return bar (x); }
+ };
+}
+
+A *a;
+
+void
+foo ()
+{
+ C c = a->baz (0);
+}
Jakub