Add reference types R32 and R64

-Add resumable_trap, safepoint, isnull, and null instructions
-Add Stackmap struct and StackmapSink trait

Co-authored-by: Mir Ahmed <mirahmed753@gmail.com>
Co-authored-by: Dan Gohman <sunfish@mozilla.com>

cranelift/filetests/src/test_safepoint.rs

@@ -0,0 +1,39 @@
+use crate::subtest::{run_filecheck, Context, SubTest, SubtestResult};
+use cranelift_codegen::ir::Function;
+use cranelift_codegen::print_errors::pretty_error;
+use cranelift_reader::TestCommand;
+use std::borrow::Cow;
+
+struct TestSafepoint;
+
+pub fn subtest(parsed: &TestCommand) -> SubtestResult<Box<SubTest>> {
+    assert_eq!(parsed.command, "safepoint");
+    if !parsed.options.is_empty() {
+        Err(format!("No options allowed on {}", parsed))
+    } else {
+        Ok(Box::new(TestSafepoint))
+    }
+}
+
+impl SubTest for TestSafepoint {
+    fn name(&self) -> &'static str {
+        "safepoint"
+    }
+
+    fn run(&self, func: Cow<Function>, context: &Context) -> SubtestResult<()> {
+        let mut comp_ctx = cranelift_codegen::Context::for_function(func.into_owned());
+
+        let isa = context.isa.expect("register allocator needs an ISA");
+        comp_ctx.compute_cfg();
+        comp_ctx
+            .legalize(isa)
+            .map_err(|e| pretty_error(&comp_ctx.func, context.isa, e))?;
+        comp_ctx.compute_domtree();
+        comp_ctx
+            .regalloc(isa)
+            .map_err(|e| pretty_error(&comp_ctx.func, context.isa, e))?;
+
+        let text = comp_ctx.func.display(context.isa).to_string();
+        run_filecheck(&text, context)
+    }
+}