[Bug c++/40389] optimizer bug (possibly)

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #13 from rguenth at gcc dot gnu dot org  2009-06-10 20:58 -------
Well.  I see as final difference (no SRA vs. with SRA)

 <bb 2>:
   D.2249 = baz (); [return slot optimization]
-  D.2417_8 = D.2249.a;
-  g.a = D.2417_8;
-  D.2415_10 = &D.2417_8->k;
+  SR.101_9 = D.2249.a;
+  SR.102_31 = D.2249.p;
+  SR.103_32 = D.2249.n;
+  g.a = SR.101_9;
+  D.2415_10 = &SR.101_9->k;
   S<H>::bar (D.2415_10, &g);
-  if (D.2417_8 != 0B)
+  if (SR.101_9 != 0B)
     goto <bb 3>;
   else
     goto <bb 9>;

 <bb 3>:
-  D.2421_13 = D.2249.p;
-  if (D.2421_13 != 0B)
+  if (SR.102_31 != 0B)
     goto <bb 4>;
   else
     goto <bb 5>;

 <bb 4>:
-  D.2422_15 = D.2249.n;
-  D.2421_13->n = D.2422_15;
+  SR.102_31->n = SR.103_32;
   goto <bb 6>;

etc.

So you say that

   D.2249 = baz (); [return slot optimization]
-  D.2417_8 = D.2249.a;
-  g.a = D.2417_8;

makes D.2249.a escape and thus

   S<H>::bar (D.2415_10, &g);

is allowed to modify D.2249.a because D.2249.a->... may point to D.2249
itself?

If

  D.2249 = baz (); [return slot optimization]

makes D.2249 escape then this is a bug in both points-to analysis and
addressability analysis (the C++ FE should then make sure to set
TREE_ADDRESSABLE on D.2249 as well if it doesn't do so already).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40389