re PR c/84607 (Side effects discarded in address computation inside 'if')

2018-02-28  Richard Biener  <rguenther@suse.de>

	PR middle-end/84607
	* genmatch.c (capture_info::walk_match): Do not mark
	captured expressions without operands as expr_p given
	they act more like predicates and should be subject to
	"lost tail" side-effect preserving.

	* gcc.dg/pr84607.c: New testcase.

From-SVN: r258061

gcc/ChangeLog

+2018-02-28  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/84607
+	* genmatch.c (capture_info::walk_match): Do not mark
+	captured expressions without operands as expr_p given
+	they act more like predicates and should be subject to
+	"lost tail" side-effect preserving.
+
 2018-02-28  Alexandre Oliva <aoliva@redhat.com>
 
 	PR rtl-optimization/81611

gcc/genmatch.c

@@ -2104,7 +2104,11 @@ capture_info::walk_match (operand *o, unsigned toplevel_arg,
       if (c->what
 	  && (e = dyn_cast <expr *> (c->what)))
 	{
-	  info[where].expr_p = true;
+	  /* Zero-operand expression captures like ADDR_EXPR@0 are
+	     similar as predicates -- if they are not mentioned in
+	     the result we have to force them to have no side-effects.  */
+	  if (e->ops.length () != 0)
+	    info[where].expr_p = true;
 	  info[where].force_single_use |= e->force_single_use;
 	}
     }

gcc/testsuite/ChangeLog

+2018-02-28  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/84607
+	* gcc.dg/pr84607.c: New testcase.
+
 2018-02-28  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/84602

gcc/testsuite/gcc.dg/pr84607.c

+/* { dg-do run } */
+
+extern void exit(int);
+extern void abort(void);
+int a[10];
+int foo()
+{
+  exit (0);
+  return 0;
+}
+int main()
+{
+  if (&a[foo()])
+    abort ();
+  return 0;
+}