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Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:

From: Andi Kleen <andi at firstfloor dot org>
To: Paolo Carlini <paolo dot carlini at oracle dot com>
Cc: Andi Kleen <andi at firstfloor dot org>, Jakub Jelinek <jakub at redhat dot com>, Richard Guenther <richard dot guenther at gmail dot com>, gcc-patches at gcc dot gnu dot org
Date: Mon, 31 May 2010 17:48:34 +0200
Subject: Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
References: <20100531081916.GA20230@basil.fritz.box> <AANLkTim92f5e_fs1K2XgOIsH_zjwOMlAoeT7uRNuawMl@mail.gmail.com> <20100531124323.GB10766@basil.fritz.box> <20100531131516.GI10293@tyan-ft48-01.lab.bos.redhat.com> <20100531142050.GC10766@basil.fritz.box> <4C03C84F.2050005@oracle.com>

On Mon, May 31, 2010 at 04:31:43PM +0200, Paolo Carlini wrote:
> On 05/31/2010 04:20 PM, Andi Kleen wrote:
> > gcc/cp/
> > 2010-05-31  Andi Kleen  <ak@linux.intel.com>
> > 	* cp/parser.cx: (cp_parser_question_colon_clause):
> >   
>     * parser.c: ...

Thanks for the crucial contribution.

Here's an updated changelog.

gcc/
2010-05-31  Andi Kleen  <ak@linux.intel.com>
	* c-parser.c (c_parser_conditional_expression):
        Call warn_for_omitted_condop.
        * c-common.c (warn_for_omitted_condop): Add.
        * c-common.h (warn_for_omitted_condop): Add prototype.
        * doc/invoke.texi: Document omitted condop warning.

gcc/testsuite/
2010-05-31  Andi Kleen  <ak@linux.intel.com>
        * gcc.dg/warn-omitted-condop.c: Add.
        * g++.dg/warn-omitted-condop.C: Add.

gcc/cp/
2010-05-31  Andi Kleen  <ak@linux.intel.com>
	* parser.c: (cp_parser_question_colon_clause):
        Switch to use cp_lexer_peek_token.
        Call warn_for_omitted_condop. Call pedwarn for omitted
        middle operand.

diff --git a/gcc/c-common.c b/gcc/c-common.c
index 115e302..1cc62a4 100644
--- a/gcc/c-common.c
+++ b/gcc/c-common.c
@@ -8588,6 +8588,18 @@ fold_offsetof (tree expr, tree stop_ref)
   return convert (size_type_node, fold_offsetof_1 (expr, stop_ref));
 }
 
+/* Warn for A ?: C expressions (with B omitted) where A is a boolean
+   expression, because B will always be true. */
+
+void
+warn_for_omitted_condop (location_t location, tree cond)
+{
+  if (truth_value_p (TREE_CODE (cond)))
+      warning_at (location, OPT_Wparentheses,
+		"the omitted middle operand in ?: will always be %<true%>, "
+		"suggest explicit middle operand");
+}
+
 /* Print an error message for an invalid lvalue.  USE says
    how the lvalue is being used and so selects the error message.  */
 
diff --git a/gcc/c-common.h b/gcc/c-common.h
index f0541e9..928242b 100644
--- a/gcc/c-common.h
+++ b/gcc/c-common.h
@@ -918,6 +918,7 @@ extern void c_parse_file (void);
 /* This is misnamed, it actually performs end-of-compilation processing.  */
 extern void finish_file	(void);
 
+extern void warn_for_omitted_condop (location_t, tree);
 
 /* These macros provide convenient access to the various _STMT nodes.  */
 
diff --git a/gcc/c-parser.c b/gcc/c-parser.c
index b30b063..42f816b 100644
--- a/gcc/c-parser.c
+++ b/gcc/c-parser.c
@@ -4795,7 +4795,7 @@ static struct c_expr
 c_parser_conditional_expression (c_parser *parser, struct c_expr *after)
 {
   struct c_expr cond, exp1, exp2, ret;
-  location_t cond_loc, colon_loc;
+  location_t cond_loc, colon_loc, middle_loc;
 
   gcc_assert (!after || c_dialect_objc ());
 
@@ -4809,8 +4809,11 @@ c_parser_conditional_expression (c_parser *parser, struct c_expr *after)
   if (c_parser_next_token_is (parser, CPP_COLON))
     {
       tree eptype = NULL_TREE;
-      pedwarn (c_parser_peek_token (parser)->location, OPT_pedantic,
+
+      middle_loc = c_parser_peek_token (parser)->location;
+      pedwarn (middle_loc, OPT_pedantic,
 	       "ISO C forbids omitting the middle term of a ?: expression");
+      warn_for_omitted_condop (middle_loc, cond.value);
       if (TREE_CODE (cond.value) == EXCESS_PRECISION_EXPR)
 	{
 	  eptype = TREE_TYPE (cond.value);
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 4a50b55..6f448b9 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -6770,15 +6770,20 @@ cp_parser_question_colon_clause (cp_parser* parser, tree logical_or_expr)
 {
   tree expr;
   tree assignment_expr;
+  struct cp_token *token;
 
   /* Consume the `?' token.  */
   cp_lexer_consume_token (parser->lexer);
+  token = cp_lexer_peek_token (parser->lexer);
   if (cp_parser_allow_gnu_extensions_p (parser)
-      && cp_lexer_next_token_is (parser->lexer, CPP_COLON))
+      && token->type == CPP_COLON)
     {
+      pedwarn (token->location, OPT_pedantic,
+               "ISO C++ does not allow ?: with omitted middle operand");
       /* Implicit true clause.  */
       expr = NULL_TREE;
       c_inhibit_evaluation_warnings += logical_or_expr == truthvalue_true_node;
+      warn_for_omitted_condop (token->location, logical_or_expr);
     }
   else
     {
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 17b1b3f..1a078ae 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3258,6 +3258,12 @@ look like this:
 @end group
 @end smallexample
 
+Also warn for dangerous uses of the
+?: with omitted middle operand GNU extension. When the condition
+in the ?: operator is a boolean expression the omitted value will
+be always 1. Often the user expects it to be a value computed
+inside the conditional expression instead.
+
 This warning is enabled by @option{-Wall}.
 
 @item -Wsequence-point
diff --git a/gcc/testsuite/g++.dg/warn/warn-omitted-condop.C b/gcc/testsuite/g++.dg/warn/warn-omitted-condop.C
new file mode 100644
index 0000000..9fda387
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/warn-omitted-condop.C
@@ -0,0 +1,58 @@
+/* { dg-options "-Wparentheses" } */
+
+extern void f2 (int);
+
+void bar (int x, int y, int z)
+{
+#define T(op) f2 (x op y ? : 1)
+#define T2(op) f2 (x op y ? 2 : 1)
+
+  T(<); /* { dg-warning "omitted middle operand" } */
+  T(>); /* { dg-warning "omitted middle operand" } */
+  T(<=); /* { dg-warning "omitted middle operand" } */
+  T(>=); /* { dg-warning "omitted middle operand" } */
+  T(==); /* { dg-warning "omitted middle operand" } */
+  T(!=); /* { dg-warning "omitted middle operand" } */
+  T(||); /* { dg-warning "omitted middle operand" } */
+  T(&&); /* { dg-warning "omitted middle operand" } */
+  f2 (!x ? : 1);  /* { dg-warning "omitted middle operand" } */
+  T2(<); /* { dg-bogus "omitted middle operand" } */
+  T2(>); /* { dg-bogus "omitted middle operand" } */
+  T2(==); /* { dg-bogus "omitted middle operand" } */
+  T2(||); /* { dg-bogus "omitted middle operand" } */
+  T2(&&); /* { dg-bogus "omitted middle operand" } */
+  T(+); /* { dg-bogus "omitted middle operand" } */
+  T(-); /* { dg-bogus "omitted middle operand" } */
+  T(*); /* { dg-bogus "omitted middle operand" } */
+  T(/); /* { dg-bogus "omitted middle operand" } */
+  T(^); /* { dg-bogus "omitted middle operand" } */
+}
+/* { dg-options "-Wparentheses" } */
+
+extern void f2 (int);
+
+void bar (int x, int y, int z)
+{
+#define T(op) f2 (x op y ? : 1)
+#define T2(op) f2 (x op y ? 2 : 1)
+
+  T(<); /* { dg-warning "omitted middle operand" } */
+  T(>); /* { dg-warning "omitted middle operand" } */
+  T(<=); /* { dg-warning "omitted middle operand" } */
+  T(>=); /* { dg-warning "omitted middle operand" } */
+  T(==); /* { dg-warning "omitted middle operand" } */
+  T(!=); /* { dg-warning "omitted middle operand" } */
+  T(||); /* { dg-warning "omitted middle operand" } */
+  T(&&); /* { dg-warning "omitted middle operand" } */
+  f2 (!x ? : 1);  /* { dg-warning "omitted middle operand" } */
+  T2(<); /* { dg-bogus "omitted middle operand" } */
+  T2(>); /* { dg-bogus "omitted middle operand" } */
+  T2(==); /* { dg-bogus "omitted middle operand" } */
+  T2(||); /* { dg-bogus "omitted middle operand" } */
+  T2(&&); /* { dg-bogus "omitted middle operand" } */
+  T(+); /* { dg-bogus "omitted middle operand" } */
+  T(-); /* { dg-bogus "omitted middle operand" } */
+  T(*); /* { dg-bogus "omitted middle operand" } */
+  T(/); /* { dg-bogus "omitted middle operand" } */
+  T(^); /* { dg-bogus "omitted middle operand" } */
+}
diff --git a/gcc/testsuite/gcc.dg/warn-omitted-condop.c b/gcc/testsuite/gcc.dg/warn-omitted-condop.c
new file mode 100644
index 0000000..9fda387
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/warn-omitted-condop.c
@@ -0,0 +1,58 @@
+/* { dg-options "-Wparentheses" } */
+
+extern void f2 (int);
+
+void bar (int x, int y, int z)
+{
+#define T(op) f2 (x op y ? : 1)
+#define T2(op) f2 (x op y ? 2 : 1)
+
+  T(<); /* { dg-warning "omitted middle operand" } */
+  T(>); /* { dg-warning "omitted middle operand" } */
+  T(<=); /* { dg-warning "omitted middle operand" } */
+  T(>=); /* { dg-warning "omitted middle operand" } */
+  T(==); /* { dg-warning "omitted middle operand" } */
+  T(!=); /* { dg-warning "omitted middle operand" } */
+  T(||); /* { dg-warning "omitted middle operand" } */
+  T(&&); /* { dg-warning "omitted middle operand" } */
+  f2 (!x ? : 1);  /* { dg-warning "omitted middle operand" } */
+  T2(<); /* { dg-bogus "omitted middle operand" } */
+  T2(>); /* { dg-bogus "omitted middle operand" } */
+  T2(==); /* { dg-bogus "omitted middle operand" } */
+  T2(||); /* { dg-bogus "omitted middle operand" } */
+  T2(&&); /* { dg-bogus "omitted middle operand" } */
+  T(+); /* { dg-bogus "omitted middle operand" } */
+  T(-); /* { dg-bogus "omitted middle operand" } */
+  T(*); /* { dg-bogus "omitted middle operand" } */
+  T(/); /* { dg-bogus "omitted middle operand" } */
+  T(^); /* { dg-bogus "omitted middle operand" } */
+}
+/* { dg-options "-Wparentheses" } */
+
+extern void f2 (int);
+
+void bar (int x, int y, int z)
+{
+#define T(op) f2 (x op y ? : 1)
+#define T2(op) f2 (x op y ? 2 : 1)
+
+  T(<); /* { dg-warning "omitted middle operand" } */
+  T(>); /* { dg-warning "omitted middle operand" } */
+  T(<=); /* { dg-warning "omitted middle operand" } */
+  T(>=); /* { dg-warning "omitted middle operand" } */
+  T(==); /* { dg-warning "omitted middle operand" } */
+  T(!=); /* { dg-warning "omitted middle operand" } */
+  T(||); /* { dg-warning "omitted middle operand" } */
+  T(&&); /* { dg-warning "omitted middle operand" } */
+  f2 (!x ? : 1);  /* { dg-warning "omitted middle operand" } */
+  T2(<); /* { dg-bogus "omitted middle operand" } */
+  T2(>); /* { dg-bogus "omitted middle operand" } */
+  T2(==); /* { dg-bogus "omitted middle operand" } */
+  T2(||); /* { dg-bogus "omitted middle operand" } */
+  T2(&&); /* { dg-bogus "omitted middle operand" } */
+  T(+); /* { dg-bogus "omitted middle operand" } */
+  T(-); /* { dg-bogus "omitted middle operand" } */
+  T(*); /* { dg-bogus "omitted middle operand" } */
+  T(/); /* { dg-bogus "omitted middle operand" } */
+  T(^); /* { dg-bogus "omitted middle operand" } */
+}


-- 
ak@linux.intel.com -- Speaking for myself only.

References:
- [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Andi Kleen
- Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Richard Guenther
- Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Andi Kleen
- Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Jakub Jelinek
- Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Andi Kleen
- Re: [PATCH] Warn for dangerous use of omitted middle operand in ?:
  - From: Paolo Carlini

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