Re: [C PATCH] Warn if switch has boolean value (PR c/60439)

[Marek Polacek <polacek at redhat dot com>]

On Fri, Apr 18, 2014 at 08:00:45AM +0200, Marek Polacek wrote:
> On Fri, Apr 18, 2014 at 07:49:22AM +0200, Marc Glisse wrote:
> > On Fri, 18 Apr 2014, Marek Polacek wrote:
> > 
> > >This patch implements a new warning that warns when controlling
> > >expression of a switch has boolean value.  (Intentionally I don't
> > >warn if the controlling expression is (un)signed:1 bit-field.)
> > >I guess the question is if this should be enabled by default or
> > >deserves some new warning option.  Since clang does the former,
> > >I did it too and currently this warning is enabled by default.
> > 
> > It can be enabled by -Wsome-name which is itself enabled by default but
> > at least gives the possibility to use -Wno-some-name, -Werror=some-name,
> > etc. No? I believe Manuel insists regularly that no new warning should
> > use 0 (and old ones should progressively lose it).
> 
> Yes, that's the other possibility and exactly what I wanted to
> discuss.  I think I'll prepare another version with -Wswitch-bool (and
> documentation).

Here.

2014-04-18  Marek Polacek  <polacek@redhat.com>

	PR c/60439
	* doc/invoke.texi: Document -Wswitch-bool.
c/
	* c-typeck.c (c_start_case): Warn if switch condition has boolean
	value.
c-family/
	* c.opt (Wswitch-bool): New option.
testsuite/
	* gcc.dg/pr60439.c: New test.

diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 390c056..9089496 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -529,6 +529,10 @@ Wswitch-enum
 C ObjC C++ ObjC++ Var(warn_switch_enum) Warning
 Warn about all enumerated switches missing a specific case
 
+Wswitch-bool
+C ObjC 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-typeck.c gcc/c/c-typeck.c
index 65aad45..44982d3 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -9344,6 +9344,28 @@ c_start_case (location_t switch_loc,
       else
 	{
 	  tree type = TYPE_MAIN_VARIANT (orig_type);
+	  tree e = exp;
+	  enum tree_code exp_code;
+
+	  while (TREE_CODE (e) == COMPOUND_EXPR)
+	    e = TREE_OPERAND (e, 1);
+	  exp_code = TREE_CODE (e);
+
+	  if (TREE_CODE (type) == BOOLEAN_TYPE
+	      || exp_code == TRUTH_ANDIF_EXPR
+	      || exp_code == TRUTH_AND_EXPR
+	      || exp_code == TRUTH_ORIF_EXPR
+	      || exp_code == TRUTH_OR_EXPR
+	      || exp_code == TRUTH_XOR_EXPR
+	      || exp_code == TRUTH_NOT_EXPR
+	      || exp_code == EQ_EXPR
+	      || exp_code == NE_EXPR
+	      || exp_code == LE_EXPR
+	      || exp_code == GE_EXPR
+	      || exp_code == LT_EXPR
+	      || exp_code == GT_EXPR)
+	    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/doc/invoke.texi gcc/doc/invoke.texi
index 8004da8..04e1c41 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -268,7 +268,7 @@ 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
@@ -3822,6 +3822,12 @@ 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.
+This warning is enabled by default for C programs.
+
 @item -Wsync-nand @r{(C and C++ only)}
 @opindex Wsync-nand
 @opindex Wno-sync-nand
diff --git gcc/testsuite/gcc.dg/pr60439.c gcc/testsuite/gcc.dg/pr60439.c
index e69de29..26e7c25 100644
--- gcc/testsuite/gcc.dg/pr60439.c
+++ gcc/testsuite/gcc.dg/pr60439.c
@@ -0,0 +1,112 @@
+/* PR c/60439 */
+/* { dg-do compile } */
+
+typedef _Bool bool;
+extern _Bool foo (void);
+
+void
+f1 (const _Bool b)
+{
+  switch (b) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f2 (int a, int b)
+{
+  switch (a && b) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch ((bool) (a && b)) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch ((a && b) || a) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f3 (int a)
+{
+  switch (!!a) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (!a) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f4 (void)
+{
+  switch (foo ()) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f5 (int a)
+{
+  switch (a == 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a != 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a > 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a < 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a <= 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a >= 3) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (foo (), foo (), a >= 42) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (a == 3, a & 4, a ^ 5, a)
+    case 1:
+      break;
+}
+
+void
+f6 (bool b)
+{
+  switch (b) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (!b) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+  switch (b++) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f7 (void)
+{
+  bool b;
+  switch (b = 1) /* { dg-warning "switch condition has boolean value" } */
+    case 1:
+      break;
+}
+
+void
+f8 (int i)
+{
+  switch (i)
+    case 0:
+      break;
+  switch ((unsigned int) i)
+    case 0:
+      break;
+  switch ((bool) i) /* { dg-warning "switch condition has boolean value" } */
+    case 0:
+      break;
+}

	Marek