gccrs: fix ICE on break with a label and a value

A `break 'label value` expression looks up a temporary variable
associated with the labeled loop to hold the value, but labeled loops
never registered that temporary, leading to an ICE in the code
generator. Register the loop result temporary against the label.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Associate the loop
	result temporary with the loop label.

gcc/testsuite/ChangeLog:

	* rust/compile/break-label-loop.rs: New test.

Signed-off-by: Lucas Ly Ba <lucas.ly-ba@outlook.com>

gcc/rust/backend/rust-compile-expr.cc

diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index 7fabc25..79fe6c4 100644
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -794,6 +794,10 @@
       ctx->add_statement (label_decl);
       ctx->insert_label_decl (
 	loop_label.get_lifetime ().get_mappings ().get_hirid (), label);
+      // Associate the loop's result temporary with the label so that a
+      // `break 'label value` can locate it (see visit (HIR::BreakExpr)).
+      ctx->insert_var_decl (
+	loop_label.get_lifetime ().get_mappings ().get_hirid (), tmp);
     }
 
   tree loop_begin_label

gcc/testsuite/rust/compile/break-label-loop.rs

diff --git a/gcc/testsuite/rust/compile/break-label-loop.rs b/gcc/testsuite/rust/compile/break-label-loop.rs
new file mode 100644
index 0000000..60169e3
--- /dev/null
+++ b/gcc/testsuite/rust/compile/break-label-loop.rs
@@ -0,0 +1,10 @@
+// `break 'label loop {}` used to ICE in the code generator because the
+// labeled loop never registered its result temporary against the label.
+#![feature(no_core)]
+#![no_core]
+
+pub fn foo() {
+    'a: loop {
+        break 'a loop {};
+    }
+}