add signed_bool_precision attribute for GIMPLE FE use

This adds __attribute__((signed_bool_precision(precision))) to be able
to construct nonstandard boolean types which for the included testcase
is needed to simulate Ada and LTO interaction (Ada uses a 8 bit
precision boolean_type_node).  This will also be useful for vector
unit testcases where we need to produce vector types with
non-standard precision signed boolean type components.

2021-01-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/95582
gcc/c-family/
	* c-attribs.c (c_common_attribute_table): Add entry for
	signed_bool_precision.
	(handle_signed_bool_precision_attribute): New.

gcc/testsuite/
	* gcc.dg/pr95582.c: New testcase.

2 files changed, 60 insertions, 0 deletions

diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index ef7cec9..84ec86b 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -161,6 +161,8 @@ static tree handle_copy_attribute (tree *, tree, tree, int, bool *);
 static tree handle_nsobject_attribute (tree *, tree, tree, int, bool *);
 static tree handle_objc_root_class_attribute (tree *, tree, tree, int, bool *);
 static tree handle_objc_nullability_attribute (tree *, tree, tree, int, bool *);
+static tree handle_signed_bool_precision_attribute (tree *, tree, tree, int,
+						    bool *);
 
 /* Helper to define attribute exclusions.  */
 #define ATTR_EXCL(name, function, type, variable)	\
@@ -274,6 +276,8 @@ const struct attribute_spec c_common_attribute_table[] =
 {
   /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
        affects_type_identity, handler, exclude } */
+  { "signed_bool_precision",  1, 1, false, true, false, true,
+			      handle_signed_bool_precision_attribute, NULL },
   { "packed",                 0, 0, false, false, false, false,
 			      handle_packed_attribute,
 	                      attr_aligned_exclusions },
@@ -894,6 +898,43 @@ validate_attr_arg (tree node[2], tree name, tree newarg)
 
 /* Attribute handlers common to C front ends.  */
 
+/* Handle a "signed_bool_precision" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_signed_bool_precision_attribute (tree *node, tree name, tree args,
+					int, bool *no_add_attrs)
+{
+  *no_add_attrs = true;
+  if (!flag_gimple)
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      return NULL_TREE;
+    }
+
+  if (!TYPE_P (*node) || TREE_CODE (*node) != BOOLEAN_TYPE)
+    {
+      warning (OPT_Wattributes, "%qE attribute only supported on "
+	       "boolean types", name);
+      return NULL_TREE;
+    }
+
+  unsigned HOST_WIDE_INT prec = HOST_WIDE_INT_M1U;
+  if (tree_fits_uhwi_p (TREE_VALUE (args)))
+    prec = tree_to_uhwi (TREE_VALUE (args));
+  if (prec > MAX_FIXED_MODE_SIZE)
+    {
+      warning (OPT_Wattributes, "%qE attribute with unsupported boolean "
+	       "precision", name);
+      return NULL_TREE;
+    }
+
+  tree new_type = build_nonstandard_boolean_type (prec);
+  *node = lang_hooks.types.reconstruct_complex_type (*node, new_type);
+
+  return NULL_TREE;
+}
+
 /* Handle a "packed" attribute; arguments as in
    struct attribute_spec.handler.  */
 
diff --git a/gcc/testsuite/gcc.dg/pr95582.c b/gcc/testsuite/gcc.dg/pr95582.c
new file mode 100644
index 0000000..cc2ab46
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr95582.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-fgimple -O3" } */
+
+typedef _Bool bool8 __attribute__((signed_bool_precision(8)));
+
+bool8 data[16];
+
+void __GIMPLE(ssa) foo(int f)
+{
+  _Bool t;
+  bool8 tp;
+
+__BB(2):
+   t_2 = f_1(D) != 0;
+   tp_3 = (bool8) t_2;
+   data[0] = tp_3;
+   data[1] = tp_3;
+   return;
+}