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Re: [C PATCH] Warn if switch has boolean value (PR c/60439)
- From: Marek Polacek <polacek at redhat dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: Steven Bosscher <stevenb dot gcc at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, "Joseph S. Myers" <joseph at codesourcery dot com>, Jason Merrill <jason at redhat dot com>
- Date: Sat, 24 May 2014 10:00:48 +0200
- Subject: Re: [C PATCH] Warn if switch has boolean value (PR c/60439)
- Authentication-results: sourceware.org; auth=none
- References: <20140418053021 dot GH20332 at redhat dot com> <CABu31nO7XjjEJCZCf_vLFgfpvuejdxcmeF6YB4++8sAGkHjJ8A at mail dot gmail dot com> <20140418115013 dot GK20332 at redhat dot com> <53632870 dot 6030503 at redhat dot com>
On Thu, May 01, 2014 at 11:09:04PM -0600, Jeff Law wrote:
> Looks reasonable, though I do wonder if we should be warning for this in the
> C++ front-end as well?
Yep, I think so. Luckily the code for the C++ FE is pretty much the
same and, in fact, simpler.
Two issues came up:
1) I think there should be a way how to suppress the warning. This
can be done by casting the value of a controlling expression to
a type other than bool. The problem was in the C FE, because the
type of expressions like && is int - so the cast to int was already
lost in c_start_case. I resorted to a not very pretty, but
hopefully simple enough hack
2) Since the warning is now enabled even for the C++ FE, it's
exercised during bootstrap. Turned out that gengtype generates
code like
switch (TREE_CODE (...) == INTEGER_TYPE) { ... }
that would mar the bootstrap - so I tweaked it to generate
switch ((int) (TREE_CODE (...) == INTEGER_TYPE) { ... })
instead. Does that make sense?
Regtested/bootstrapped on x86_64-linux, ok for trunk?
2014-05-24 Marek Polacek <polacek@redhat.com>
PR c/60439
* doc/invoke.texi: Document -Wswitch-bool.
* function.c (stack_protect_epilogue): Cast controlling expression of
the switch to int.
* gengtype.c (walk_type): Generate switch expression with its
controlling expression cast to int.
c/
* c-parser.c (c_parser_switch_statement): Pass explicit_cast_p to
c_start_case.
* c-tree.h (c_start_case): Update.
* c-typeck.c (c_start_case): Add new boolean parameter. Warn if
switch condition has boolean value.
cp/
* semantics.c (finish_switch_cond): Warn if switch condition has
boolean value.
c-family/
* c.opt (Wswitch-bool): New option.
testsuite/
* c-c++-common/pr60439.c: New test.
* g++.dg/eh/scope1.C (f4): Add dg-warning.
diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index c586e65..5d36a80 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -534,6 +534,10 @@ Wswitch-enum
C ObjC C++ ObjC++ Var(warn_switch_enum) Warning
Warn about all enumerated switches missing a specific case
+Wswitch-bool
+C ObjC C++ ObjC++ Warning Init(1)
+Warn about switches with boolean controlling expression
+
Wmissing-format-attribute
C ObjC C++ ObjC++ Alias(Wsuggest-attribute=format)
;
diff --git gcc/c/c-parser.c gcc/c/c-parser.c
index 88edf36..fc4865e 100644
--- gcc/c/c-parser.c
+++ gcc/c/c-parser.c
@@ -5196,9 +5196,13 @@ c_parser_switch_statement (c_parser *parser)
gcc_assert (c_parser_next_token_is_keyword (parser, RID_SWITCH));
c_parser_consume_token (parser);
block = c_begin_compound_stmt (flag_isoc99);
+ bool explicit_cast_p = false;
if (c_parser_require (parser, CPP_OPEN_PAREN, "expected %<(%>"))
{
switch_cond_loc = c_parser_peek_token (parser)->location;
+ if (c_parser_next_token_is (parser, CPP_OPEN_PAREN)
+ && c_token_starts_typename (c_parser_peek_2nd_token (parser)))
+ explicit_cast_p = true;
ce = c_parser_expression (parser);
ce = convert_lvalue_to_rvalue (switch_cond_loc, ce, true, false);
expr = ce.value;
@@ -5216,7 +5220,7 @@ c_parser_switch_statement (c_parser *parser)
switch_cond_loc = UNKNOWN_LOCATION;
expr = error_mark_node;
}
- c_start_case (switch_loc, switch_cond_loc, expr);
+ c_start_case (switch_loc, switch_cond_loc, expr, explicit_cast_p);
save_break = c_break_label;
c_break_label = NULL_TREE;
body = c_parser_c99_block_statement (parser);
diff --git gcc/c/c-tree.h gcc/c/c-tree.h
index e7dcb35..133930f 100644
--- gcc/c/c-tree.h
+++ gcc/c/c-tree.h
@@ -614,7 +614,7 @@ extern void process_init_element (location_t, struct c_expr, bool,
struct obstack *);
extern tree build_compound_literal (location_t, tree, tree, bool);
extern void check_compound_literal_type (location_t, struct c_type_name *);
-extern tree c_start_case (location_t, location_t, tree);
+extern tree c_start_case (location_t, location_t, tree, bool);
extern void c_finish_case (tree);
extern tree build_asm_expr (location_t, tree, tree, tree, tree, tree, bool);
extern tree build_asm_stmt (tree, tree);
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 74a5ebd..24958c4 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -9347,12 +9347,13 @@ struct c_switch *c_switch_stack;
/* Start a C switch statement, testing expression EXP. Return the new
SWITCH_EXPR. SWITCH_LOC is the location of the `switch'.
- SWITCH_COND_LOC is the location of the switch's condition. */
+ SWITCH_COND_LOC is the location of the switch's condition.
+ EXPLICIT_CAST_P is true if the expression EXP has explicit cast. */
tree
c_start_case (location_t switch_loc,
location_t switch_cond_loc,
- tree exp)
+ tree exp, bool explicit_cast_p)
{
tree orig_type = error_mark_node;
struct c_switch *cs;
@@ -9373,6 +9374,19 @@ c_start_case (location_t switch_loc,
else
{
tree type = TYPE_MAIN_VARIANT (orig_type);
+ tree e = exp;
+
+ /* Warn if the condition has boolean value. */
+ while (TREE_CODE (e) == COMPOUND_EXPR)
+ e = TREE_OPERAND (e, 1);
+
+ if ((TREE_CODE (type) == BOOLEAN_TYPE
+ || truth_value_p (TREE_CODE (e)))
+ /* Explicit cast to int suppresses this warning. */
+ && !(TREE_CODE (type) == INTEGER_TYPE
+ && explicit_cast_p))
+ warning_at (switch_cond_loc, OPT_Wswitch_bool,
+ "switch condition has boolean value");
if (!in_system_header_at (input_location)
&& (type == long_integer_type_node
diff --git gcc/cp/semantics.c gcc/cp/semantics.c
index edab330..0f65ace 100644
--- gcc/cp/semantics.c
+++ gcc/cp/semantics.c
@@ -1129,6 +1129,17 @@ finish_switch_cond (tree cond, tree switch_stmt)
orig_type = TREE_TYPE (cond);
if (cond != error_mark_node)
{
+ /* Warn if the condition has boolean value. */
+ tree e = cond;
+ while (TREE_CODE (e) == COMPOUND_EXPR)
+ e = TREE_OPERAND (e, 1);
+
+ if (TREE_CODE (orig_type) == BOOLEAN_TYPE
+ || (truth_value_p (TREE_CODE (e))
+ && TREE_CODE (orig_type) != INTEGER_TYPE))
+ warning_at (input_location, OPT_Wswitch_bool,
+ "switch condition has boolean value");
+
/* [stmt.switch]
Integral promotions are performed. */
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index 34ba721..b1f36bf 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -271,7 +271,7 @@ Objective-C and Objective-C++ Dialects}.
-Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
-Wmissing-format-attribute @gol
--Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
+-Wswitch -Wswitch-default -Wswitch-enum -Wswitch-bool -Wsync-nand @gol
-Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol
-Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol
-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
@@ -3845,6 +3845,22 @@ between @option{-Wswitch} and this option is that this option gives a
warning about an omitted enumeration code even if there is a
@code{default} label.
+@item -Wswitch-bool
+@opindex Wswitch-bool
+@opindex Wno-switch-bool
+Warn whenever a @code{switch} statement has an index of boolean type.
+It is possible to suppress this warning by casting the controlling
+expression to a type other than @code{bool}. For example:
+@smallexample
+@group
+switch ((int) (a == 4))
+ @{
+ ...
+ @}
+@end group
+@end smallexample
+This warning is enabled by default for C and C++ programs.
+
@item -Wsync-nand @r{(C and C++ only)}
@opindex Wsync-nand
@opindex Wno-sync-nand
diff --git gcc/function.c gcc/function.c
index ec2ea26..922f567 100644
--- gcc/function.c
+++ gcc/function.c
@@ -4649,7 +4649,7 @@ stack_protect_epilogue (void)
/* Allow the target to compare Y with X without leaking either into
a register. */
- switch (HAVE_stack_protect_test != 0)
+ switch ((int) (HAVE_stack_protect_test != 0))
{
case 1:
tmp = gen_stack_protect_test (x, y, label);
diff --git gcc/gengtype.c gcc/gengtype.c
index 808ef45..9da6545 100644
--- gcc/gengtype.c
+++ gcc/gengtype.c
@@ -3099,9 +3099,9 @@ walk_type (type_p t, struct walk_type_data *d)
t->u.s.tag);
desc = "1";
}
- oprintf (d->of, "%*sswitch (", d->indent, "");
+ oprintf (d->of, "%*sswitch ((int) (", d->indent, "");
output_escaped_param (d, desc, "desc");
- oprintf (d->of, ")\n");
+ oprintf (d->of, "))\n");
d->indent += 2;
oprintf (d->of, "%*s{\n", d->indent, "");
}
@@ -3121,9 +3121,9 @@ walk_type (type_p t, struct walk_type_data *d)
"missing `tag' option for type `%s'",
t->u.s.tag);
}
- oprintf (d->of, "%*sswitch (", d->indent, "");
+ oprintf (d->of, "%*sswitch ((int) (", d->indent, "");
output_escaped_param (d, desc, "desc");
- oprintf (d->of, ")\n");
+ oprintf (d->of, "))\n");
d->indent += 2;
oprintf (d->of, "%*s{\n", d->indent, "");
oprintf (d->of, "%*scase %s:\n", d->indent, "", type_tag);
diff --git gcc/testsuite/c-c++-common/pr60439.c gcc/testsuite/c-c++-common/pr60439.c
index e69de29..89288d7 100644
--- gcc/testsuite/c-c++-common/pr60439.c
+++ gcc/testsuite/c-c++-common/pr60439.c
@@ -0,0 +1,108 @@
+/* PR c/60439 */
+/* { dg-do compile } */
+
+#ifndef __cplusplus
+# define bool _Bool
+#endif
+
+extern bool foo (void);
+
+void
+f1 (bool b)
+{
+ switch (b) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
+
+void
+f2 (int a, int b)
+{
+ switch (a && b) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch ((bool) (a && b)) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch ((a && b) || a) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ /* No warnings on following. */
+ switch ((int) (a && b))
+ break;
+ switch ((unsigned int) (a && b))
+ break;
+ switch ((unsigned short int) (a && b))
+ break;
+ switch ((char) (a && b))
+ break;
+}
+
+void
+f3 (int a)
+{
+ switch (!!a) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (!a) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
+
+void
+f4 (void)
+{
+ switch (foo ()) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
+
+void
+f5 (int a)
+{
+ switch (a == 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a != 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a > 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a < 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a <= 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a >= 3) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (foo (), foo (), a >= 42) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (a == 3, a & 4, a ^ 5, a)
+ break;
+ switch ((int) (a == 3))
+ break;
+ switch ((int) (a != 3))
+ break;
+}
+
+void
+f6 (bool b)
+{
+ switch (b) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (!b) /* { dg-warning "switch condition has boolean value" } */
+ break;
+ switch (b++) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
+
+void
+f7 (void)
+{
+ bool b;
+ switch (b = 1) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
+
+void
+f8 (int i)
+{
+ switch (i)
+ break;
+ switch ((int) i)
+ break;
+ switch ((unsigned int) i)
+ break;
+ switch ((bool) i) /* { dg-warning "switch condition has boolean value" } */
+ break;
+}
diff --git gcc/testsuite/g++.dg/eh/scope1.C gcc/testsuite/g++.dg/eh/scope1.C
index 276e0d6..4884ec7 100644
--- gcc/testsuite/g++.dg/eh/scope1.C
+++ gcc/testsuite/g++.dg/eh/scope1.C
@@ -31,7 +31,7 @@ void f3 ()
void f4 ()
{
- switch (C br = C())
+ switch (C br = C()) /* { dg-warning "switch condition has boolean value" } */
{
default:
abort ();
Marek