[Bug c/84607] [6/7/8 Regression] Side effects discarded in address computation inside 'if'

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84607

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
             Status|UNCONFIRMED                 |ASSIGNED
      Known to work|                            |5.5.0
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2018-02-28
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org
     Ever confirmed|0                           |1
            Summary|Side effects discarded in   |[6/7/8 Regression] Side
                   |address computation inside  |effects discarded in
                   |'if'                        |address computation inside
                   |                            |'if'
   Target Milestone|---                         |6.5
      Known to fail|                            |6.1.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Note the same issue happens when using the C++ frontend.  IL
difference between 5.5 and 6.1:

--- t.c.003t.original   2018-02-28 09:47:04.783058082 +0100
+++ t.c.003t.original.6 2018-02-28 09:46:55.318915245 +0100
@@ -14,7 +14,7 @@


 {
-  if (&a[foo ()];, 1)
+  if (1)
     {
       puts ((const char *) "goodbye");
     }

so it looks like some folding issue.

Triggered by

 (simplify
  (cmp (convert? addr@0) integer_zerop)
  (if (tree_single_nonzero_warnv_p (@0, NULL))
   { constant_boolean_node (cmp == NE_EXPR, type); })))

which implements itself as

8294    /* #line 3553 "/space/rguenther/src/svn/early-lto-debug/gcc/match.pd"
*/
8295      if (tree_single_nonzero_warnv_p (captures[0], NULL))
8296        {
8297          if (TREE_SIDE_EFFECTS (op1)) return NULL_TREE;

^^^ this should have checked op0!

8298          if (dump_file && (dump_flags & TDF_FOLDING)) fprintf (dump_file,
"Applying pattern match.pd:3554, %s:%d\n", __FILE__, __LINE__);
8299          tree res;
8300          res =  constant_boolean_node (cmp == NE_EXPR, type);
8301          return res;