Address review comments:

- Undo temporary changes to default features (`all-arch`) and a
  signal-handler test.
- Remove `SIGTRAP` handler: no longer needed now that we've found an
  "undefined opcode" option on ARM64.
- Rename pp.rs to pretty_print.rs in machinst/.
- Only use empty stack-probe on non-x86. As per a comment in
  rust-lang/compiler-builtins [1], LLVM only supports stack probes on
  x86 and x86-64. Thus, on any other CPU architecture, we cannot refer
  to `__rust_probestack`, because it does not exist.
- Rename arm64 to aarch64.
- Use `target` directive in vcode filetests.
- Run the flags verifier, but without encinfo, when using new backends.
- Clean up warning overrides.
- Fix up use of casts: use u32::from(x) and siblings when possible,
  u32::try_from(x).unwrap() when not, to avoid silent truncation.
- Take immutable `Function` borrows as input; we don't actually
  mutate the input IR.
- Lots of other miscellaneous cleanups.

[1] cae3e6ea23/src/probestack.rs (L39)

cranelift/codegen/src/context.rs

@@ -180,8 +180,7 @@ impl Context {
         }
 
         if let Some(backend) = isa.get_mach_backend() {
-            let func = std::mem::replace(&mut self.func, Function::new());
-            let result = backend.compile_function(func, self.want_disasm)?;
+            let result = backend.compile_function(&mut self.func, self.want_disasm)?;
             let info = result.code_info();
             self.mach_compile_result = Some(result);
             Ok(info)
@@ -312,15 +311,15 @@ impl Context {
 
     /// Run the legalizer for `isa` on the function.
     pub fn legalize(&mut self, isa: &dyn TargetIsa) -> CodegenResult<()> {
+        // Legalization invalidates the domtree and loop_analysis by mutating the CFG.
+        // TODO: Avoid doing this when legalization doesn't actually mutate the CFG.
+        self.domtree.clear();
+        self.loop_analysis.clear();
         if isa.get_mach_backend().is_some() {
             // Run some specific legalizations only.
             simple_legalize(&mut self.func, &mut self.cfg, isa);
-            Ok(())
+            self.verify_if(isa)
         } else {
-            // Legalization invalidates the domtree and loop_analysis by mutating the CFG.
-            // TODO: Avoid doing this when legalization doesn't actually mutate the CFG.
-            self.domtree.clear();
-            self.loop_analysis.clear();
             legalize_function(&mut self.func, &mut self.cfg, isa);
             debug!("Legalized:\n{}", self.func.display(isa));
             self.verify_if(isa)