c: Diagnose char argument to __builtin_stdc_*

When working on __builtin_stdc_rotate_*, I've noticed that while the
second argument to those is explicitly allowed to have char type,
the first argument to all the stdc_* type-generic functions is
- standard unsigned integer type, excluding bool;
- extended unsigned integer type;
- or, bit-precise unsigned integer type whose width matches a standard
  or extended integer type, excluding bool.
but the __builtin_stdc_* lowering code was diagnosing just
!INTEGRAL_TYPE_P
ENUMERAL_TYPE
BOOLEAN_TYPE
!TYPE_UNSIGNED
Now, with -funsigned-char plain char type is TYPE_UNSIGNED, yet it isn't
allowed because it isn't standard unsigned integer type, nor
extended unsigned integer type, nor bit-precise unsigned integer type.

The following patch diagnoses char arguments and adds testsuite coverage
for that.

Or should I make it a pedwarn instead?

2024-10-30  Jakub Jelinek  <jakub@redhat.com>

gcc/c/
	* c-parser.cc (c_parser_postfix_expression): Diagnose if
	first __builtin_stdc_* argument has char type even when
	-funsigned-char.
gcc/testsuite/
	* gcc.dg/builtin-stdc-bit-3.c: New test.
	* gcc.dg/builtin-stdc-rotate-3.c: New test.

3 files changed, 38 insertions, 0 deletions

diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 88dd0be..90c3397 100644
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -12382,6 +12382,14 @@ c_parser_postfix_expression (c_parser *parser)
 		expr.set_error ();
 		break;
 	      }
+	    if (TYPE_MAIN_VARIANT (TREE_TYPE (arg_p->value))
+		== char_type_node)
+	      {
+		error_at (loc, "argument 1 in call to function "
+			  "%qs has %<char%> type", name);
+		expr.set_error ();
+		break;
+	      }
 	    tree arg = arg_p->value;
 	    tree type = TYPE_MAIN_VARIANT (TREE_TYPE (arg));
 	    /* Expand:
diff --git a/gcc/testsuite/gcc.dg/builtin-stdc-bit-3.c b/gcc/testsuite/gcc.dg/builtin-stdc-bit-3.c
new file mode 100644
index 0000000..bb73768
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/builtin-stdc-bit-3.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-funsigned-char" } */
+
+void
+foo (void)
+{
+  __builtin_stdc_leading_zeros ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_leading_zeros' has 'char' type" } */
+  __builtin_stdc_leading_ones ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_leading_ones' has 'char' type" } */
+  __builtin_stdc_trailing_zeros ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_trailing_zeros' has 'char' type" } */
+  __builtin_stdc_trailing_ones ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_trailing_ones' has 'char' type" } */
+  __builtin_stdc_first_leading_zero ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_first_leading_zero' has 'char' type" } */
+  __builtin_stdc_first_leading_one ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_first_leading_one' has 'char' type" } */
+  __builtin_stdc_first_trailing_zero ((char) 0);	/* { dg-error "argument 1 in call to function '__builtin_stdc_first_trailing_zero' has 'char' type" } */
+  __builtin_stdc_first_trailing_one ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_first_trailing_one' has 'char' type" } */
+  __builtin_stdc_count_zeros ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_count_zeros' has 'char' type" } */
+  __builtin_stdc_count_ones ((char) 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_count_ones' has 'char' type" } */
+  __builtin_stdc_has_single_bit ((char) 0);		/* { dg-error "argument 1 in call to function '__builtin_stdc_has_single_bit' has 'char' type" } */
+  __builtin_stdc_bit_width ((char) 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_bit_width' has 'char' type" } */
+  __builtin_stdc_bit_floor ((char) 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_bit_floor' has 'char' type" } */
+  __builtin_stdc_bit_ceil ((char) 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_bit_ceil' has 'char' type" } */
+}
diff --git a/gcc/testsuite/gcc.dg/builtin-stdc-rotate-3.c b/gcc/testsuite/gcc.dg/builtin-stdc-rotate-3.c
new file mode 100644
index 0000000..6eac145
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/builtin-stdc-rotate-3.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-funsigned-char" } */
+
+void
+foo (void)
+{
+  __builtin_stdc_rotate_left ((char) 0, 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_rotate_left' has 'char' type" } */
+  __builtin_stdc_rotate_right ((char) 0, 0);			/* { dg-error "argument 1 in call to function '__builtin_stdc_rotate_right' has 'char' type" } */
+}