gccrs: Fix ICE when compiling block expressions in array capacity

We need to reuse the existing compile_constant_item helper which handles
the case if this is a simple expression, fn-call or a block expression.
The patch extracts out this helper as a static method so this can be used
in more places.

Fixes Rust-GCC#3566

gcc/rust/ChangeLog:

	* backend/rust-compile-base.cc (HIRCompileBase::address_expression): new helper constexpr
	* backend/rust-compile-base.h: prototype
	* backend/rust-compile-type.cc (TyTyResolveCompile::visit): call constexpr helper

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3566-1.rs: New test.
	* rust/compile/issue-3566-2.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

2 files changed, 30 insertions, 0 deletions

diff --git a/gcc/testsuite/rust/compile/issue-3566-1.rs b/gcc/testsuite/rust/compile/issue-3566-1.rs
new file mode 100644
index 0000000..b7e5be0
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3566-1.rs
@@ -0,0 +1,8 @@
+mod a {
+    pub mod b {
+
+        pub fn f(x: [u8; { 100 }]) -> [u8; { 100 }] {
+            x
+        }
+    }
+}
diff --git a/gcc/testsuite/rust/compile/issue-3566-2.rs b/gcc/testsuite/rust/compile/issue-3566-2.rs
new file mode 100644
index 0000000..3f3ea73
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-3566-2.rs
@@ -0,0 +1,22 @@
+// run-pass
+
+#![allow(H8)]
+#![allow(dead_code)]
+
+
+// pretty-expanded FIXME #23616
+
+mod a {
+    pub mod b {
+        pub type t = isize;
+
+        pub fn f(x: [u8; { let s = 17; 100 }]) -> [u8;  { let z = 18; 100 }] {
+    //~^ WARN unused variable: `s`
+    //~| WARN unused variable: `z`
+    x
+}
+    }
+}
+
+pub fn main() {    //~ ERROR cannot move out
+    }