Allow for unencoded instructions in the binemit tests.

If an instruction doesn't have an associated encoding, use the standard
TargetIsa hook to encode it.

The test still fails if an instruction can't be encoded. There is no
legalization step.

docs/testing.rst

@@ -336,3 +336,11 @@ that instruction is compared to the directive::
         [R#200c,%x8]        v11 = isub v1, v2       ; bin: 40628433
         return
     }
+
+If any instructions are unencoded (indicated with a `[-]` encoding field), they
+will be encoded using the same mechanism as the legalizer uses. However,
+illegal instructions for the ISA won't be expanded into other instruction
+sequences. Instead the test will fail.
+
+Value locations must be present if they are required to compute the binary
+bits. Missing value locations will cause the test to crash.

filetests/isa/riscv/binary32.cton

@@ -6,7 +6,7 @@ function int32() {
 ebb0:
     [-,%x5]             v1 = iconst.i32 1
     [-,%x6]             v2 = iconst.i32 2
-    [R#0c,%x7]          v10 = iadd v1, v2       ; bin: 006283b3
+    [-,%x7]             v10 = iadd v1, v2       ; bin: 006283b3
     [R#200c,%x8]        v11 = isub v1, v2       ; bin: 40628433
     [R#10c]             v12 = imul v1, v2
     return

src/filetest/binemit.rs

@@ -3,7 +3,7 @@
 //! The `binemit` test command generates binary machine code for every instruction in the input
 //! functions and compares the results to the expected output.
 
-use std::borrow::{Borrow, Cow};
+use std::borrow::Cow;
 use std::fmt::Write;
 use cretonne::binemit;
 use cretonne::ir;
@@ -60,7 +60,7 @@ impl SubTest for TestBinEmit {
     }
 
     fn is_mutating(&self) -> bool {
-        false
+        true
     }
 
     fn needs_isa(&self) -> bool {
@@ -71,7 +71,7 @@ impl SubTest for TestBinEmit {
         let isa = context.isa.expect("binemit needs an ISA");
         // TODO: Run a verifier pass over the code first to detect any bad encodings or missing/bad
         // value locations. The current error reporting is just crashing...
-        let func = func.borrow();
+        let mut func = func.into_owned();
 
         let mut sink = TextSink { text: String::new() };
 
@@ -85,6 +85,22 @@ impl SubTest for TestBinEmit {
                                            comment.text))
                     }
                 };
+
+                // Compute an encoding for `inst` if one wasn't provided.
+                if !func.encodings
+                        .get(inst)
+                        .map(|e| e.is_legal())
+                        .unwrap_or(false) {
+                    match isa.encode(&func.dfg, &func.dfg[inst]) {
+                        Ok(enc) => *func.encodings.ensure(inst) = enc,
+                        Err(_) => {
+                            return Err(format!("{} can't be encoded: {}",
+                                               inst,
+                                               func.dfg.display_inst(inst)))
+                        }
+                    }
+                }
+
                 sink.text.clear();
                 isa.emit_inst(&func, inst, &mut sink);
                 let have = sink.text.trim();