Teach vrp that THIS pointer and references are non-zero

[Jan Hubicka]

Hi,
with multiple inheritance compiling the testcase bellow, the first call always
leads to call with offseted pointer, while the other call results in if
conditoinal testing if parameter is non-NULL.

This patch teach VRP that THIS pointers and references are non-zero.  I hope
this is true also for fortran and ada, but I think both languages do not really
have NULL.

I think VRP could basically assume all reference pointers to be non-zero, but
I am not sure how to do that with GIMPLE useless conversion rules.

Bootstrapped/regtested x86_64-linux, OK?

Honza

        * g++.dg/tree-ssa/nonzero-3.C: New testcase.
        * tree-vrp.c (nonnull_arg_p): THIS pointers and references are non-zero.
        (gimple_stmt_nonzero_warnv_p): Reference return values are non-zero.
Index: testsuite/g++.dg/tree-ssa/nonzero-3.C
===================================================================
--- testsuite/g++.dg/tree-ssa/nonzero-3.C       (revision 0)
+++ testsuite/g++.dg/tree-ssa/nonzero-3.C       (working copy)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
+struct A {int a;};
+struct B {int b;};
+struct C:A,B {int c;
+  void bar();};
+
+void foo (struct B *);
+void C::bar ()
+{
+  struct C *d = this;
+  foo(this);
+  foo(d);
+}
+void bar (struct C &c)
+{
+  struct C *d = &c;
+  foo(&c);
+  foo(d);
+}
+/* { dg-final { scan-tree-dump-not "if \\(" "vrp1"} } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */
Index: tree-vrp.c
===================================================================
--- tree-vrp.c  (revision 222016)
+++ tree-vrp.c  (working copy)
@@ -393,6 +393,17 @@ nonnull_arg_p (const_tree arg)
   if (arg == cfun->static_chain_decl)
     return true;
 
+  /* THIS argument of method is always non-NULL.  */
+  if (TREE_CODE (TREE_TYPE (current_function_decl)) == METHOD_TYPE
+      && arg == DECL_ARGUMENTS (current_function_decl)
+      && flag_delete_null_pointer_checks)
+    return true;
+
+  /* Values passed by reference are always non-NULL.  */
+  if (TREE_CODE (TREE_TYPE (arg)) == REFERENCE_TYPE
+      && flag_delete_null_pointer_checks)
+    return true;
+
   fntype = TREE_TYPE (current_function_decl);
   for (attrs = TYPE_ATTRIBUTES (fntype); attrs; attrs = TREE_CHAIN (attrs))
     {
@@ -1216,6 +1227,10 @@ gimple_stmt_nonzero_warnv_p (gimple stmt
            && DECL_IS_OPERATOR_NEW (fndecl)
            && !TREE_NOTHROW (fndecl))
          return true;
+       /* Referneces are alwyas non-NULL.  */
+       if (flag_delete_null_pointer_checks
+           && TREE_CODE (TREE_TYPE (fndecl)) == REFERENCE_TYPE)
+         return true;
        if (flag_delete_null_pointer_checks && 
            lookup_attribute ("returns_nonnull",
                              TYPE_ATTRIBUTES (gimple_call_fntype (stmt))))