d: Ensure casting from bool results in either 0 or 1 (PR96435)

If casting from bool, the result is either 0 or 1, any other value
violates @safe code, so enforce that it is never invalid.

	PR d/96435

gcc/d/ChangeLog:

	* d-convert.cc (convert_for_rvalue): New function.
	* d-tree.h (convert_for_rvalue): Declare.
	* expr.cc (ExprVisitor::visit (CastExp *)): Use convert_for_rvalue.
	(build_return_dtor): Likewise.

gcc/testsuite/ChangeLog:

	* gdc.dg/torture/pr96435.d: New test.

1 files changed, 21 insertions, 0 deletions

diff --git a/gcc/testsuite/gdc.dg/torture/pr96435.d b/gcc/testsuite/gdc.dg/torture/pr96435.d
new file mode 100644
index 0000000..c6d8785
--- /dev/null
+++ b/gcc/testsuite/gdc.dg/torture/pr96435.d
@@ -0,0 +1,21 @@
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96435
+// { dg-do run }
+
+@safe bool test96435()
+{
+    int[2] array = [16, 678];
+    union U { int i; bool b; }
+    U u;
+    u.i = 0xDEADBEEF;
+    assert(array[u.b] == 678);
+    return u.b;
+}
+
+@safe void main()
+{
+    auto b = test96435();
+    if (b)
+        assert(true);
+    if (!b)
+        assert(false);
+}