Use a unique ISA in 'test cat' file tests.

Add a Function::display() method which can include ISA-specific
information when printing the function.

If a test file has a unique ISA, use that in the `test cat`
implementation.

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)
     }
 }

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)

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>,
 }