[PATCH] Fix PR84607

[Richard Biener]

genmatch was fooled by singelton expression leafs so it omitted
the required TREE_SIDE_EFFECTS check and building a COMPOUND_EXPR
for the side-effects.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2018-02-28  Richard Biener  <rguent...@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.

Index: gcc/genmatch.c
===================================================================
--- gcc/genmatch.c      (revision 258056)
+++ gcc/genmatch.c      (working copy)
@@ -2104,7 +2104,11 @@ capture_info::walk_match (operand *o, un
       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;
        }
     }
Index: gcc/testsuite/gcc.dg/pr84607.c
===================================================================
--- gcc/testsuite/gcc.dg/pr84607.c      (nonexistent)
+++ gcc/testsuite/gcc.dg/pr84607.c      (working copy)
@@ -0,0 +1,16 @@
+/* { 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;
+}