diff --git a/cranelift/filetests/parser/instruction_encoding.cton b/cranelift/filetests/parser/instruction_encoding.cton
index 49c1913bcf..0e40d0b2f1 100644
--- a/cranelift/filetests/parser/instruction_encoding.cton
+++ b/cranelift/filetests/parser/instruction_encoding.cton
@@ -17,9 +17,9 @@ ebb1(v0: i32, v1: i32):
 ; nextln: $ebb1($v0: i32, $v1: i32):
 ; nextln:     [-]$WS $v2 = iadd $v0, $v1
 ; nextln:     [-]$WS trap
-; nextln:     [0#1234]$WS $v6, $v7 = iadd_cout $v2, $v0
+; nextln:     [R#1234]$WS $v6, $v7 = iadd_cout $v2, $v0
 ; TODO Add the full encoding information available: instruction recipe name and architectural registers if specified
-; nextln:     [2#beef]$WS $v8 = ishl_imm $v6, 2
+; nextln:     [Rshamt#beef]$WS $v8 = ishl_imm $v6, 2
 ; nextln:     [-]$WS $v9 = iadd $v8, $v7
-; nextln:     [3#05]$WS return $v0, $v8
-; nextln: }
\ No newline at end of file
+; nextln:     [Iret#05]$WS return $v0, $v8
+; nextln: }
diff --git a/cranelift/src/cat.rs b/cranelift/src/cat.rs
index 443c37dadc..fd49722ec0 100644
--- a/cranelift/src/cat.rs
+++ b/cranelift/src/cat.rs
@@ -61,6 +61,6 @@ impl SubTest for TestCat {
     }
 
     fn run(&self, func: Cow<Function>, context: &Context) -> STResult<()> {
-        subtest::run_filecheck(&func.to_string(), context)
+        subtest::run_filecheck(&func.display(context.isa).to_string(), context)
     }
 }
diff --git a/cranelift/src/filetest/runone.rs b/cranelift/src/filetest/runone.rs
index 06e4cfce6b..2067a245b9 100644
--- a/cranelift/src/filetest/runone.rs
+++ b/cranelift/src/filetest/runone.rs
@@ -90,7 +90,10 @@ fn test_tuples<'a>(tests: &'a [Box<SubTest>],
                 }
             }
         } else {
-            out.push((&**test, no_isa_flags, None));
+            // This test doesn't require an ISA, and we only want to run one instance of it.
+            // Still, give it an ISA ref if we happen to have a unique one.
+            // For example, `test cat` can use this to print encodings and register names.
+            out.push((&**test, no_isa_flags, isa_spec.unique_isa()));
         }
     }
     Ok(out)
diff --git a/cranelift/src/filetest/subtest.rs b/cranelift/src/filetest/subtest.rs
index 8ba3528a6c..170490fb3a 100644
--- a/cranelift/src/filetest/subtest.rs
+++ b/cranelift/src/filetest/subtest.rs
@@ -10,7 +10,7 @@ use filecheck::{self, CheckerBuilder, Checker, Value as FCValue};
 
 pub type Result<T> = result::Result<T, String>;
 
-/// Context for running a a test on a single function.
+/// Context for running a test on a single function.
 pub struct Context<'a> {
     /// Comments from the preamble f the test file. These apply to all functions.
     pub preamble_comments: &'a [Comment<'a>],
@@ -24,8 +24,8 @@ pub struct Context<'a> {
     /// ISA-independent flags for this test.
     pub flags: &'a Flags,
 
-    /// Target ISA to test against. Only present for sub-tests whose `needs_isa` method returned
-    /// true.
+    /// Target ISA to test against. Only guaranteed to be present for sub-tests whose `needs_isa`
+    /// method returned `true`. For other sub-tests, this is set if the test file has a unique ISA.
     pub isa: Option<&'a TargetIsa>,
 }
 
diff --git a/lib/cretonne/src/ir/function.rs b/lib/cretonne/src/ir/function.rs
index b0115a70e3..1abf9c4b35 100644
--- a/lib/cretonne/src/ir/function.rs
+++ b/lib/cretonne/src/ir/function.rs
@@ -6,7 +6,7 @@
 use std::fmt::{self, Display, Debug, Formatter};
 use ir::{FunctionName, Signature, Value, Inst, StackSlot, StackSlotData, JumpTable, JumpTableData,
          ValueLoc, DataFlowGraph, Layout};
-use isa::Encoding;
+use isa::{TargetIsa, Encoding};
 use entity_map::{EntityMap, PrimaryEntityData};
 use write::write_function;
 
@@ -64,6 +64,20 @@ impl Function {
     pub fn new() -> Function {
         Self::with_name_signature(FunctionName::default(), Signature::new())
     }
+
+    /// Return an object that can display this function with correct ISA-specific annotations.
+    pub fn display<'a, I: Into<Option<&'a TargetIsa>>>(&'a self, isa: I) -> DisplayFunction<'a> {
+        DisplayFunction(self, isa.into())
+    }
+}
+
+/// Wrapper type capable of displaying a `Function` with correct ISA annotations.
+pub struct DisplayFunction<'a>(&'a Function, Option<&'a TargetIsa>);
+
+impl<'a> Display for DisplayFunction<'a> {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        write_function(fmt, self.0, self.1)
+    }
 }
 
 impl Display for Function {