Re: PR c++/36921 [4.3/4.4 Regression] warning "comparison does not have mathematical meaning" is not correct for overloaded operators that do not return boolean

["Manuel López-Ibáñez" <lopezibanez@gmail.com>]

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2008/10/25 Jakub Jelinek <jakub@redhat.com>:
>
> Are you sure we don't want to warn even about the:
>  if (code == EQ_EXPR || code == NE_EXPR)
>    {
>      if (TREE_CODE_CLASS (code_left) == tcc_comparison
>          || TREE_CODE_CLASS (code_right) == tcc_comparison)
>        warning (OPT_Wparentheses,
>                 "suggest parentheses around comparison in operand of %s",
>                 code == EQ_EXPR ? "==" : "!=");
>    }
> case if EQ_EXPR or NE_EXPR don't return boolean?

Thanks. I added your suggestion. Bootstrapped and regression tested on
x86_64-unknown-linux-gnu with --enable-languages=all.

OK for trunk?

2008-11-04  Manuel López-Ibáñez  <manu@gcc.gnu.org>

	PR c++/36921
cp/
	* typeck.c (build_x_binary_op): Do not warn for overloaded
	comparison operators that do not return boolean.
testsuite/
	* g++.dg/warn/pr36921.C: New.

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Index: gcc/testsuite/g++.dg/warn/pr36921.C
===================================================================
--- gcc/testsuite/g++.dg/warn/pr36921.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/pr36921.C	(revision 0)
@@ -0,0 +1,27 @@
+/* PR 36921: comparison operator can be overloaded. Do not emit
+   warnings in such case.
+ { dg-do compile }
+ { dg-options "-Wparentheses" }
+*/
+struct A {};
+A operator<(A, A) { return A(); }
+A operator>(A, A) { return A(); }
+A operator<=(A, A) { return A(); }
+A operator>=(A, A) { return A(); }
+A operator==(A, A) { return A(); }
+A operator!=(A, A) { return A(); }
+
+int main() {
+  A() < A() < A(); // should not emit warning
+  1 < 2 < 3; // { dg-warning "mathematical meaning" "parentheses" }
+  A() > A() > A(); // should not emit warning
+  1 > 2 > 3; // { dg-warning "mathematical meaning" "parentheses" }
+  A() <= A() <= A(); // should not emit warning
+  1 <= 2 <= 3; // { dg-warning "mathematical meaning" "parentheses" }
+  A() >= A() >= A(); // should not emit warning
+  1 >= 2 >= 3; // { dg-warning "mathematical meaning" "parentheses" }
+
+  A() == A() < A (); // { dg-warning "suggest parentheses" "parentheses" }
+  A() < A() != A (); // { dg-warning "suggest parentheses" "parentheses" }
+  return 0;
+}
Index: gcc/cp/typeck.c
===================================================================
--- gcc/cp/typeck.c	(revision 141531)
+++ gcc/cp/typeck.c	(working copy)
@@ -3155,11 +3155,17 @@ build_x_binary_op (enum tree_code code, 
   if (warn_parentheses
       && !processing_template_decl
       && !error_operand_p (arg1)
       && !error_operand_p (arg2)
       && (code != LSHIFT_EXPR
-	  || !CLASS_TYPE_P (TREE_TYPE (arg1))))
+	  || !CLASS_TYPE_P (TREE_TYPE (arg1)))
+      /* Do not warn about overloaded comparison operator that does
+	 not return boolean.  */
+      && (TREE_CODE_CLASS (code) != tcc_comparison 
+	  || code == EQ_EXPR 
+	  || code == NE_EXPR
+	  || TREE_CODE (TREE_TYPE (expr)) == BOOLEAN_TYPE))
     warn_about_parentheses (code, arg1_code, orig_arg1, arg2_code, orig_arg2);
 
   if (processing_template_decl && expr != error_mark_node)
     return build_min_non_dep (code, expr, orig_arg1, orig_arg2);