Add a Context::emit_to_memory function.

This function will emit the binary machine code into contiguous raw
memory while sending relocations to a RelocSink.

Add a MemoryCodeSink for generating machine code directly into memory
efficiently. Allow the TargetIsa to provide emit_function
implementations that are specialized to the MemoryCodeSink type to avoid
needless small virtual callbacks to put1() et etc.

lib/cretonne/src/context.rs

@@ -9,7 +9,7 @@
 //! contexts concurrently. Typically, you would have one context per compilation thread and only a
 //! single ISA instance.
 
-use binemit::{CodeOffset, relax_branches};
+use binemit::{CodeOffset, relax_branches, MemoryCodeSink, RelocSink};
 use dominator_tree::DominatorTree;
 use flowgraph::ControlFlowGraph;
 use ir::Function;
@@ -71,6 +71,16 @@ impl Context {
         self.relax_branches(isa)
     }
 
+    /// Emit machine code directly into raw memory.
+    ///
+    /// Write all of the function's machine code to the memory at `mem`. The size of the machine
+    /// code is returned by `compile` above.
+    ///
+    /// The machine code is not relocated. Instead, any relocations are emitted into `relocs`.
+    pub fn emit_to_memory(&self, mem: *mut u8, relocs: &mut RelocSink, isa: &TargetIsa) {
+        isa.emit_function(&self.func, &mut MemoryCodeSink::new(mem, relocs));
+    }
+
     /// Run the verifier on the function.
     ///
     /// Also check that the dominator tree and control flow graph are consistent with the function.