Fix PR ipa/60965 (placement new wrt ipa-devirt)
Jan Hubicka
hubicka@ucw.cz
Mon May 5 19:44:00 GMT 2014
Hi,
this patch fixes unfortunate thinko in get_class_context that invalidates
transitions from non-POD type to a polymorphic type that may happen by virtue
of placement new and apparently breaks openJDK and Qt. I really tried to keep
placement new in mind when implementing ipa-devirt, so hope there are no
similar negaitve surprises.
The patch disables about 200 out of 30000 devirtualizations happening in
Firefox.
I have commited it to 4.9 and will commit to mainline once testing finishes.
Honza
PR ipa/60965
* g++.dg/ipa/devirt-31.C: New testcase.
* g++.dg/ipa/devirt-11.C: Adjust testcase.
* ipa-devirt.c (get_class_context): Allow POD to change to non-POD.
Index: testsuite/g++.dg/ipa/devirt-31.C
===================================================================
--- testsuite/g++.dg/ipa/devirt-31.C (revision 0)
+++ testsuite/g++.dg/ipa/devirt-31.C (revision 0)
@@ -0,0 +1,23 @@
+/* { dg-options "-O2 -std=c++11 -fdump-ipa-inline" } */
+#include <new>
+
+class EmbeddedObject {
+public:
+ virtual int val() { return 2; }
+};
+
+class Container {
+ alignas(EmbeddedObject) char buffer[sizeof(EmbeddedObject)];
+public:
+ EmbeddedObject *obj() { return (EmbeddedObject*)buffer; }
+ Container() { new (buffer) EmbeddedObject(); }
+};
+
+Container o;
+
+int main()
+{
+ __builtin_printf("%d\n", o.obj()->val());
+}
+/* { dg-final { scan-ipa-dump-not "__builtin_unreachable" "inline" } } */
+/* { dg-final { cleanup-ipa-dump "inline" } } */
Index: testsuite/g++.dg/ipa/devirt-11.C
===================================================================
--- testsuite/g++.dg/ipa/devirt-11.C (revision 210049)
+++ testsuite/g++.dg/ipa/devirt-11.C (working copy)
@@ -45,5 +45,5 @@ bar ()
/* While inlining function called once we should devirtualize a new call to fn2
and two to fn3. While doing so the new symbol for fn2 needs to be
introduced. */
-/* { dg-final { scan-ipa-dump-times "Discovered a virtual call to a known target" 3 "inline" } } */
+/* { dg-final { scan-ipa-dump-times "Discovered a virtual call to a known target" 1 "inline" } } */
/* { dg-final { cleanup-ipa-dump "inline" } } */
Index: ipa-devirt.c
===================================================================
--- ipa-devirt.c (revision 210049)
+++ ipa-devirt.c (working copy)
@@ -987,6 +987,17 @@ give_up:
context->outer_type = expected_type;
context->offset = 0;
context->maybe_derived_type = true;
+ context->maybe_in_construction = true;
+ /* POD can be changed to an instance of a polymorphic type by
+ placement new. Here we play safe and assume that any
+ non-polymorphic type is POD. */
+ if ((TREE_CODE (type) != RECORD_TYPE
+ || !TYPE_BINFO (type)
+ || !polymorphic_type_binfo_p (TYPE_BINFO (type)))
+ && (TREE_CODE (TYPE_SIZE (type)) != INTEGER_CST
+ || (offset + tree_to_uhwi (TYPE_SIZE (expected_type)) <=
+ tree_to_uhwi (TYPE_SIZE (type)))))
+ return true;
return false;
}
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