Generate binemit::emit_inst() functions.

Use the meta language encoding recipes to generate an emit_inst()
function for each ISA. The generated calls into recipe_*() functions
that must be implemented by hand.

Implement recipe_*() functions for the RISC-V recipes.

Add the TargetIsa::emit_inst() entry point which emits an instruction to
a CodeSink trait object.

lib/cretonne/meta/build.py

@@ -12,6 +12,7 @@ import gen_build_deps
 import gen_encoding
 import gen_legalizer
 import gen_registers
+import gen_binemit
 
 parser = argparse.ArgumentParser(description='Generate sources for Cretonne.')
 parser.add_argument('--out-dir', help='set output directory')
@@ -27,4 +28,5 @@ gen_settings.generate(isas, out_dir)
 gen_encoding.generate(isas, out_dir)
 gen_legalizer.generate(isas, out_dir)
 gen_registers.generate(isas, out_dir)
+gen_binemit.generate(isas, out_dir)
 gen_build_deps.generate()

lib/cretonne/meta/gen_binemit.py

@@ -0,0 +1,46 @@
+"""
+Generate binary emission code for each ISA.
+"""
+
+from __future__ import absolute_import
+import srcgen
+
+try:
+    from typing import Sequence, List  # noqa
+    from cdsl.isa import TargetISA  # noqa
+except ImportError:
+    pass
+
+
+def gen_isa(isa, fmt):
+    # type: (TargetISA, srcgen.Formatter) -> None
+    """
+    Generate Binary emission code for `isa`.
+    """
+    fmt.doc_comment(
+            '''
+            Emit binary machine code for `inst` for the {} ISA.
+            '''.format(isa.name))
+    if len(isa.all_recipes) == 0:
+        # No encoding recipes: Emit a stub.
+        with fmt.indented(
+                'pub fn emit_inst<CS: CodeSink + ?Sized>'
+                '(func: &Function, inst: Inst, _sink: &mut CS) {', '}'):
+            fmt.line('bad_encoding(func, inst)')
+    else:
+        with fmt.indented(
+                'pub fn emit_inst<CS: CodeSink + ?Sized>'
+                '(func: &Function, inst: Inst, sink: &mut CS) {', '}'):
+            with fmt.indented('match func.encodings[inst].recipe() {', '}'):
+                for i, recipe in enumerate(isa.all_recipes):
+                    fmt.line('{} => recipe_{}(func, inst, sink),'.format(
+                        i, recipe.name.lower()))
+                fmt.line('_ => bad_encoding(func, inst),')
+
+
+def generate(isas, out_dir):
+    # type: (Sequence[TargetISA], str) -> None
+    for isa in isas:
+        fmt = srcgen.Formatter()
+        gen_isa(isa, fmt)
+        fmt.update_file('binemit-{}.rs'.format(isa.name), out_dir)