[C++ Patch] PR 52299, bogus div by zero warning

[Paolo Carlini]

Hi,

I handled this issue as outlined by Jakub in the audit trail. For the 
purpose of the bogus div by zero warning just using 
c_inhibit_evaluation_warnings appears to work fine.

Tested x86_64-linux.

Thanks,
Paolo.

///////////////////////
/cp
2012-03-12  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/52299
        * pt.c (tsubst_copy_and_build, case COND_EXPR): Avoid bogus
        division by zero warnings.

/testsuite
2012-03-12  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/52299
        * g++.dg/warn/Wdiv-by-zero-bogus.C: New.

Index: testsuite/g++.dg/warn/Wdiv-by-zero-bogus.C
===================================================================
--- testsuite/g++.dg/warn/Wdiv-by-zero-bogus.C  (revision 0)
+++ testsuite/g++.dg/warn/Wdiv-by-zero-bogus.C  (revision 0)
@@ -0,0 +1,30 @@
+// PR c++/52299
+
+template<unsigned x>
+struct test0 {
+  static const unsigned a_
+  = x ? 10 / x : 10;
+};
+
+template<unsigned x>
+struct test1 {
+  static const unsigned a_
+  = !x ? 10 : 10 / x;
+};
+
+template<bool x>
+struct test2 {
+  static const unsigned a_
+  = x ? 10 / x : 10;
+};
+
+template<bool x>
+struct test3 {
+  static const unsigned a_
+  = !x ? 10 : 10 / x;
+};
+
+unsigned i0 = test0<0>::a_;
+unsigned i1 = test1<0>::a_;
+unsigned i2 = test2<false>::a_;
+unsigned i3 = test3<false>::a_;
Index: cp/pt.c
===================================================================
--- cp/pt.c     (revision 185247)
+++ cp/pt.c     (working copy)
@@ -13943,12 +13943,36 @@ tsubst_copy_and_build (tree t,
       }
 
     case COND_EXPR:
-      return build_x_conditional_expr
-       (RECUR (TREE_OPERAND (t, 0)),
-        RECUR (TREE_OPERAND (t, 1)),
-        RECUR (TREE_OPERAND (t, 2)),
-         complain);
+      {
+       tree cond = RECUR (TREE_OPERAND (t, 0));
+       tree op1, op2;
 
+       if (TREE_CODE (cond) == INTEGER_CST)
+         {
+           if (integer_zerop (cond))
+             {
+               ++c_inhibit_evaluation_warnings;
+               op1 = RECUR (TREE_OPERAND (t, 1));
+               --c_inhibit_evaluation_warnings;
+               op2 = RECUR (TREE_OPERAND (t, 2));
+             }
+           else
+             {
+               op1 = RECUR (TREE_OPERAND (t, 1));
+               ++c_inhibit_evaluation_warnings;
+               op2 = RECUR (TREE_OPERAND (t, 2));
+               --c_inhibit_evaluation_warnings;
+             }
+         }
+       else
+         {
+           op1 = RECUR (TREE_OPERAND (t, 1));
+           op2 = RECUR (TREE_OPERAND (t, 2));
+         }
+
+       return build_x_conditional_expr (cond, op1, op2, complain);
+      }
+
     case PSEUDO_DTOR_EXPR:
       return finish_pseudo_destructor_expr
        (RECUR (TREE_OPERAND (t, 0)),