[Bug tree-optimization/69682] New: expression (a && (b==c)) with side effects rewritten to ((b==c) & a)

["mtliang at synopsys dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69682

            Bug ID: 69682
           Summary: expression (a && (b==c)) with side effects rewritten
                    to ((b==c) & a)
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mtliang at synopsys dot com
  Target Milestone: ---

Created attachment 37586
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37586&action=edit
test case

The attached test case should print pass in a cases but fails with SIGFPE when
built at -O1 and run with "1" to enable signaling NaNs.

Building with -fdump-tree-all shows that at -O0 the 004t.gimple for { if (same
&& (oldPriority == oldGroup)); } expands into { if (same) if (oldPriority ==
oldGroup); } as expected, but that at -O1 it's already transformed into { if
(oldPriority == oldGroup) & same); } .

At this point, oldPriority holds a signaling NaN but shouldn't be evaluated
because same is false.

With -fverbose-asm, I've gotten the 30+ extra flags that are set between -O0
and -O1 and have tried building the code with -O0 + all flags and with -O1 +
-fno-flags.  Neither way seems to make any difference.

By the way, even if the initial tree is generated properly, there is another
known issue where ifcombine will join them together again and that step will
need to be suppressed for testing purposes.  See bug 69308 for details.