[C++ PATCH] Fix replace_placeholders (PR c++/83556)

[Jakub Jelinek]

Hi!

Recently I've changed replace_placeholders to walk trees without duplicates
to avoid compile time explosion with lots of nested SAVE_EXPRs.
The problem as the following testcase shows is that it also prevents
replacement of PLACEHOLDER_EXPRs we want to replace, if the same
PLACEHOLDER_EXPR appears multiple time in the expression.

The following patch changes the walk_tree not to use pset itself, but rather
stops walking children if we've seen some tree already.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/7.3?

2017-12-23  Jakub Jelinek  <ja...@redhat.com>

        PR c++/83556
        * tree.c (replace_placeholders_r): Pass NULL as last argument to
        cp_walk_tree instead of d->pset.  If non-TREE_CONSTANT and
        non-PLACEHOLDER_EXPR tree has been seen already, set *walk_subtrees
        to false and return.
        (replace_placeholders): Pass NULL instead of &pset as last argument
        to cp_walk_tree.

        * g++.dg/cpp0x/pr83556.C: New test.

--- gcc/cp/tree.c.jj    2017-12-15 16:10:37.000000000 +0100
+++ gcc/cp/tree.c       2017-12-22 23:24:16.720428548 +0100
@@ -3106,6 +3106,11 @@ replace_placeholders_r (tree* t, int* wa
       {
        constructor_elt *ce;
        vec<constructor_elt,va_gc> *v = CONSTRUCTOR_ELTS (*t);
+       if (d->pset->add (*t))
+         {
+           *walk_subtrees = false;
+           return NULL_TREE;
+         }
        for (unsigned i = 0; vec_safe_iterate (v, i, &ce); ++i)
          {
            tree *valp = &ce->value;
@@ -3125,7 +3130,7 @@ replace_placeholders_r (tree* t, int* wa
                  valp = &TARGET_EXPR_INITIAL (*valp);
              }
            d->obj = subob;
-           cp_walk_tree (valp, replace_placeholders_r, data_, d->pset);
+           cp_walk_tree (valp, replace_placeholders_r, data_, NULL);
            d->obj = obj;
          }
        *walk_subtrees = false;
@@ -3133,6 +3138,8 @@ replace_placeholders_r (tree* t, int* wa
       }
 
     default:
+      if (d->pset->add (*t))
+       *walk_subtrees = false;
       break;
     }
 
@@ -3161,7 +3168,7 @@ replace_placeholders (tree exp, tree obj
   replace_placeholders_t data = { obj, false, &pset };
   if (TREE_CODE (exp) == TARGET_EXPR)
     tp = &TARGET_EXPR_INITIAL (exp);
-  cp_walk_tree (tp, replace_placeholders_r, &data, &pset);
+  cp_walk_tree (tp, replace_placeholders_r, &data, NULL);
   if (seen_p)
     *seen_p = data.seen;
   return exp;
--- gcc/testsuite/g++.dg/cpp0x/pr83556.C.jj     2017-12-22 23:30:10.771126002 
+0100
+++ gcc/testsuite/g++.dg/cpp0x/pr83556.C        2017-12-22 23:29:21.000000000 
+0100
@@ -0,0 +1,28 @@
+// PR c++/83556
+// { dg-do run { target c++11 } }
+
+int
+foo ()
+{
+  return 1;
+}
+
+struct A
+{
+  int a = foo ();
+  int b = 1;
+  int c = a ? 1 * b : 2 * b;
+};
+
+struct B
+{
+  A d {};
+};
+
+int
+main ()
+{
+  B e {};
+  if (e.d.c != 1)
+    __builtin_abort ();
+}

        Jakub