Patchwork C++ PATCH for c++/48909 (constexpr ICE)

login
register
mail settings
Submitter Jason Merrill
Date May 6, 2011, 9:47 p.m.
Message ID <4DC46C60.4000304@redhat.com>
Download mbox | patch
Permalink /patch/94437/
State New
Headers show

Comments

Jason Merrill - May 6, 2011, 9:47 p.m.
Here, the problem was that in

(*(first + 1) < *first) != false

integral promotion changes the < expr to have type int.  Then 
fold_binary_op_with_conditional_arg wants to change this to

(*(first + 1) < *first) ? true : false

without changing the type, so the condition of a ?: has the wrong type 
by the time we get to the constexpr expander.  For 4.6, it seems 
simplest to fix this by making the constexpr code more permissive.

Tested x86_64-pc-linux-gnu, applying to 4.6 and trunk.
commit 1be580e74a6e959ffaa041b49be08c895d44eb01
Author: Jason Merrill <jason@redhat.com>
Date:   Fri May 6 10:48:52 2011 -0400

    	PR c++/48909
    	* semantics.c (cxx_eval_conditional_expression): Check
    	integer_zerop/onep instead.

Patch

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index d0c559b..cc8db90 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -6299,13 +6299,12 @@  cxx_eval_conditional_expression (const constexpr_call *call, tree t,
 					   allow_non_constant, addr,
 					   non_constant_p);
   VERIFY_CONSTANT (val);
-  if (val == boolean_true_node)
-    return cxx_eval_constant_expression (call, TREE_OPERAND (t, 1),
+  /* Don't VERIFY_CONSTANT the other operands.  */
+  if (integer_zerop (val))
+    return cxx_eval_constant_expression (call, TREE_OPERAND (t, 2),
 					 allow_non_constant, addr,
 					 non_constant_p);
-  gcc_assert (val == boolean_false_node);
-  /* Don't VERIFY_CONSTANT here.  */
-  return cxx_eval_constant_expression (call, TREE_OPERAND (t, 2),
+  return cxx_eval_constant_expression (call, TREE_OPERAND (t, 1),
 				       allow_non_constant, addr,
 				       non_constant_p);
 }
@@ -7872,12 +7871,12 @@  potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
       tmp = TREE_OPERAND (t, 0);
       if (!potential_constant_expression_1 (tmp, rval, flags))
 	return false;
-      else if (tmp == boolean_true_node)
-	return potential_constant_expression_1 (TREE_OPERAND (t, 1),
-						want_rval, flags);
-      else if (tmp == boolean_false_node)
+      else if (integer_zerop (tmp))
 	return potential_constant_expression_1 (TREE_OPERAND (t, 2),
 						want_rval, flags);
+      else if (TREE_CODE (tmp) == INTEGER_CST)
+	return potential_constant_expression_1 (TREE_OPERAND (t, 1),
+						want_rval, flags);
       for (i = 1; i < 3; ++i)
 	if (potential_constant_expression_1 (TREE_OPERAND (t, i),
 					     want_rval, tf_none))
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-condition2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-condition2.C
new file mode 100644
index 0000000..2434096
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-condition2.C
@@ -0,0 +1,18 @@ 
+// PR c++/48909
+// { dg-options -std=c++0x }
+
+#define SA(X) static_assert((X),#X)
+
+constexpr int const * is_sorted_until(int const * first, int const * last)
+{
+ return first == last || first + 1 == last ? last
+  : (*(first + 1) < *first) != false ? first + 1
+  : is_sorted_until(first + 1, last);
+}
+
+int main()
+{
+ static constexpr int array[2] = {0, 1};
+ constexpr int const * last = is_sorted_until(array, array + 2);
+ SA(last==array+2);
+}