[PATCH, PR 52939] Gracefully deal with fold_ctor_reference returning NULL during devirtualization

[Martin Jambor <mjambor at suse dot cz>]

Hi,

currently we ICE when attempting to devirtualize a call to a virtual
method introduced in a descendant but with a base which is an ancestor
which does not have it.  This is because fold_ctor_reference returns
constant zero when it cannot find the particular value in the provided
constructor which is something gimple_get_virt_method_for_binfo cannot
cope with.  The patch below avoids it by simply testing for that
value and bailing out.

Bootstrapped and tested on x86_64-linux, OK for trunk?

Thanks,

Martin


2012-04-12  Martin Jambor  <mjambor@suse.cz>

	PR middle-end/52939
	* gimple-fold.c (gimple_get_virt_method_for_binfo): Bail out if
	fold_ctor_reference returns a zero constant.

	* testsuite/g++.dg/ipa/pr52939.C: New test.

Index: src/gcc/gimple-fold.c
===================================================================
--- src.orig/gcc/gimple-fold.c
+++ src/gcc/gimple-fold.c
@@ -3087,7 +3087,7 @@ gimple_get_virt_method_for_binfo (HOST_W
   offset += token * size;
   fn = fold_ctor_reference (TREE_TYPE (TREE_TYPE (v)), DECL_INITIAL (v),
 			    offset, size);
-  if (!fn)
+  if (!fn || integer_zerop (fn))
     return NULL_TREE;
   gcc_assert (TREE_CODE (fn) == ADDR_EXPR
 	      || TREE_CODE (fn) == FDESC_EXPR);
Index: src/gcc/testsuite/g++.dg/ipa/pr52939.C
===================================================================
--- /dev/null
+++ src/gcc/testsuite/g++.dg/ipa/pr52939.C
@@ -0,0 +1,58 @@
+/* Verify that we do not ICE on invalid devirtualizations (which might
+   be OK at run-time because never executed).  */
+/* { dg-do run } */
+/* { dg-options "-O3 -fno-early-inlining -fno-inline"  } */
+
+extern "C" void abort (void);
+
+class A
+{
+public:
+  int data;
+  virtual int foo (int i);
+};
+
+class B : public A
+{
+public:
+  virtual int foo (int i);
+  virtual int bar (int i);
+};
+
+int A::foo (int i)
+{
+  return i + 1;
+}
+
+int B::foo (int i)
+{
+  return i + 2;
+}
+
+int B::bar (int i)
+{
+  return i + 3;
+}
+
+static int middleman (class A *obj, int i)
+{
+  class B *b = (class B *) obj;
+
+  if (i != 1)
+    return b->bar (i);
+  else
+    return i;
+}
+
+int __attribute__ ((noinline,noclone)) get_input(void)
+{
+  return 1;
+}
+
+int main (int argc, char *argv[])
+{
+  class A o;
+  if (middleman (&o, get_input ()) != 1)
+    abort ();
+  return 0;
+}