diff mbox

[C++] Further fix for constexpr SAVE_EXPR loop handling (PR c++/70135)

Message ID 20160308181247.GD3017@tucnak.redhat.com
State New
Headers show

Commit Message

Jakub Jelinek March 8, 2016, 6:12 p.m. UTC 
Hi!

The following testcases show that the recent cxx_eval_loop_expr
fix wasn't sufficient in certain cases, it works well if the
SAVE_EXPR contains increment of iterator that is initialized to some
constant before the loop, but if we have nested loops and might look up
the SAVE_EXPR again (usually by processing the LOOP_EXPR again), we can
get stale values.

Fixed by forgetting the saved SAVE_EXPR values at the end of the loop too,
not just in between iterations.

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

2016-03-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/70135
	* constexpr.c (cxx_eval_loop_expr): Forget saved values of SAVE_EXPRs
	even after the last iteration of the loop.

	* g++.dg/cpp1y/constexpr-loop4.C: New test.
	* g++.dg/ubsan/pr70135.C: New test.


	Jakub

Comments

Jason Merrill March 8, 2016, 7:57 p.m. UTC | #1 
OK, thanks.

Jason
diff mbox

Patch

--- gcc/cp/constexpr.c.jj	2016-03-08 09:01:48.000000000 +0100
+++ gcc/cp/constexpr.c	2016-03-08 16:36:27.192053214 +0100
@@ -3165,21 +3165,21 @@  cxx_eval_loop_expr (const constexpr_ctx
   constexpr_ctx new_ctx = *ctx;
 
   tree body = TREE_OPERAND (t, 0);
-  while (true)
+  do
     {
       hash_set<tree> save_exprs;
       new_ctx.save_exprs = &save_exprs;
 
       cxx_eval_statement_list (&new_ctx, body,
 			       non_constant_p, overflow_p, jump_target);
-      if (returns (jump_target) || breaks (jump_target) || *non_constant_p)
-	break;
 
       /* Forget saved values of SAVE_EXPRs.  */
       for (hash_set<tree>::iterator iter = save_exprs.begin();
 	   iter != save_exprs.end(); ++iter)
 	new_ctx.values->remove (*iter);
     }
+  while (!returns (jump_target) && !breaks (jump_target) && !*non_constant_p);
+
   if (breaks (jump_target))
     *jump_target = NULL_TREE;
 
--- gcc/testsuite/g++.dg/cpp1y/constexpr-loop4.C.jj	2016-03-08 16:35:01.352224129 +0100
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-loop4.C	2016-03-08 16:34:32.000000000 +0100
@@ -0,0 +1,27 @@ 
+// { dg-do compile { target c++14 } }
+
+struct A
+{
+  int i;
+};
+
+constexpr bool f()
+{
+  A ar[5] = { 6, 7, 8, 9, 10 };
+  A *ap = ar;
+  int i = 0, j = 0;
+  for (j = 0; j < 2; j++)
+    {
+      do
+	*ap++ = A{i};
+      while (++i < j * 2 + 2);
+    }
+  return (ar[0].i == 0
+	  && ar[1].i == 1
+	  && ar[2].i == 2
+	  && ar[3].i == 3
+	  && ar[4].i == 10);
+}
+
+#define SA(X) static_assert((X),#X)
+SA(f());
--- gcc/testsuite/g++.dg/ubsan/pr70135.C.jj	2016-03-08 16:16:06.863701979 +0100
+++ gcc/testsuite/g++.dg/ubsan/pr70135.C	2016-03-08 16:17:26.850610633 +0100
@@ -0,0 +1,36 @@ 
+// PR c++/70135
+// { dg-do run }
+// { dg-options "-fsanitize=bounds -std=c++14" }
+
+template <bool... b>
+struct S {
+  static constexpr bool c[] {b...};
+  static constexpr auto foo ()
+  {
+    unsigned long n = 0;
+    for (unsigned long i = 0; i < sizeof (c); i++)
+      if (!c[i])
+	++n;
+    return n;
+  }
+  static constexpr auto n = foo () + 1;
+  static constexpr auto bar ()
+  {
+    int h = 0;
+    for (int g = 0, i = 0; g < n; ++g)
+      {
+	while (i < sizeof...(b) && c[i++])
+	  ++h;
+	h += 64;
+      }
+    return h;
+  }
+};
+
+int
+main ()
+{
+  S <true, false, false, true, true, true, false, true> s;
+  constexpr auto c = s.bar ();
+  static_assert (s.bar () == 4 * 64 + 5);
+}