Add a convenience function for displaying a BlockCall (#5677)

Add a display method to BlockCall that returns a std::fmt::Displayable result. Rework the display code in the write module of cranelift-codegen to use this method instead.

cranelift/codegen/src/ir/instructions.rs

@@ -118,6 +118,35 @@ impl BlockCall {
     {
         self.values.extend(elements, pool)
     }
+
+    /// Return a value that can display this block call.
+    pub fn display<'a>(&self, pool: &'a ValueListPool) -> DisplayBlockCall<'a> {
+        DisplayBlockCall { block: *self, pool }
+    }
+}
+
+/// Wrapper for the context needed to display a [BlockCall] value.
+pub struct DisplayBlockCall<'a> {
+    block: BlockCall,
+    pool: &'a ValueListPool,
+}
+
+impl<'a> Display for DisplayBlockCall<'a> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.block.block(&self.pool))?;
+        let args = self.block.args_slice(&self.pool);
+        if !args.is_empty() {
+            write!(f, "(")?;
+            for (ix, arg) in args.iter().enumerate() {
+                if ix > 0 {
+                    write!(f, ", ")?;
+                }
+                write!(f, "{}", arg)?;
+            }
+            write!(f, ")")?;
+        }
+        Ok(())
+    }
 }
 
 // Include code generated by `cranelift-codegen/meta/src/gen_inst.rs`. This file contains: