Add an Encoding meta-language class.

Start adding some RISC-V encodings too as a way of testing the ergonomics.

meta/cretonne/__init__.py

@@ -671,6 +671,16 @@ class CPUMode(object):
     def __init__(self, name, target):
         self.name = name
         self.target = target
+        self.encodings = []
+
+    def enc(self, *args, **kwargs):
+        """
+        Add a new encoding to this CPU mode.
+
+        Arguments are the `Encoding constructor arguments, except for the first
+        `CPUMode argument which is implied.
+        """
+        self.encodings.append(Encoding(self, *args, **kwargs))
 
 
 class EncRecipe(object):
@@ -689,6 +699,46 @@ class EncRecipe(object):
         self.name = name
         self.format = format
 
+
+class Encoding(object):
+    """
+    Encoding for a concrete instruction.
+
+    An `Encoding` object ties an instruction opcode with concrete type
+    variables together with and encoding recipe and encoding bits.
+
+    :param cpumode: The CPU mode where the encoding is active.
+    :param inst: The :py:class:`Instruction` being encoded.
+    :param typevars: Concete types for `inst`'s type variables, if any.
+    :param recipe: The :py:class:`EncRecipe` to use.
+    :param encbits: Additional encoding bits to be interpreted by `recipe`.
+    """
+
+    def __init__(self, cpumode, inst, typevars, recipe, encbits):
+        assert isinstance(cpumode, CPUMode)
+        assert isinstance(inst, Instruction)
+        assert isinstance(recipe, EncRecipe)
+        self.cpumode = cpumode
+        assert inst.format == recipe.format, (
+                "Format {} must match recipe: {}".format(
+                    inst.format, recipe.format))
+        self.inst = inst
+        self.typevars = self._to_type_tuple(typevars)
+        self.recipe = recipe
+        self.encbits = encbits
+
+    @staticmethod
+    def _to_type_tuple(x):
+        # Allow a single ValueType instance instead of the awkward singleton
+        # tuple syntax.
+        if isinstance(x, ValueType):
+            x = (x,)
+        else:
+            x = tuple(x)
+        for ty in x:
+            assert isinstance(ty, ValueType)
+        return x
+
 # Import the fixed instruction formats now so they can be added to the
 # registry.
 importlib.import_module('cretonne.formats')

meta/target/riscv/__init__.py

@@ -25,11 +25,9 @@ RV32G / RV64G
 
 """
 
-from cretonne import Target, CPUMode
-import cretonne.base
+import defs
+import encodings
 
-target = Target('riscv', [cretonne.base.instructions])
+# Re-export the primary target definition.
+target = defs.target
 
-# CPU modes for 32-bit and 64-bit operation.
-RV32 = CPUMode('RV32', target)
-RV64 = CPUMode('RV64', target)

meta/target/riscv/defs.py

@@ -0,0 +1,14 @@
+"""
+RISC-V definitions.
+
+Commonly used definitions.
+"""
+
+from cretonne import Target, CPUMode
+import cretonne.base
+
+target = Target('riscv', [cretonne.base.instructions])
+
+# CPU modes for 32-bit and 64-bit operation.
+RV32 = CPUMode('RV32', target)
+RV64 = CPUMode('RV64', target)

meta/target/riscv/encodings.py

@@ -0,0 +1,21 @@
+"""
+RISC-V Encodings.
+"""
+from cretonne import base
+from cretonne.types import i32, i64
+from defs import RV32, RV64
+from recipes import OP, R
+
+# Basic arithmetic binary instructions are encoded in an R-type instruction.
+for inst,           f3,    f7 in [
+        (base.iadd, 0b000, 0b0000000),
+        (base.isub, 0b000, 0b0100000),
+        (base.ishl, 0b001, 0b0000000),
+        (base.ushr, 0b101, 0b0000000),
+        (base.sshr, 0b101, 0b0100000),
+        (base.bxor, 0b100, 0b0000000),
+        (base.bor,  0b110, 0b0000000),
+        (base.band, 0b111, 0b0000000)
+        ]:
+    RV32.enc(inst, i32, R, OP(f3, f7))
+    RV64.enc(inst, i64, R, OP(f3, f7))

meta/target/riscv/recipes.py

@@ -0,0 +1,44 @@
+"""
+RISC-V Encoding recipes.
+
+The encoding recipes defined here more or less correspond to the RISC-V native
+instruction formats described in the reference:
+
+    The RISC-V Instruction Set Manual
+    Volume I: User-Level ISA
+    Version 2.1
+"""
+from cretonne import EncRecipe
+from cretonne.formats import Binary
+
+# The low 7 bits of a RISC-V instruction is the base opcode. All 32-bit
+# instructions have 11 as the two low bits, with bits 6:2 determining the base
+# opcode.
+#
+# Encbits for the 32-bit recipes are opcode[6:2] | (funct3 << 5) | ...
+# The functions below encode the encbits.
+
+def LOAD(funct3):
+    assert funct3 <= 0b111
+    return 0b00000 | (funct3 << 5)
+
+def STORE(funct3):
+    assert funct3 <= 0b111
+    return 0b01000 | (funct3 << 5)
+
+def BRANCH(funct3):
+    assert funct3 <= 0b111
+    return 0b11000 | (funct3 << 5)
+
+def OPIMM(funct3):
+    assert funct3 <= 0b111
+    return 0b00100 | (funct3 << 5)
+
+def OP(funct3, funct7):
+    assert funct3 <= 0b111
+    assert funct7 <= 0b1111111
+    return 0b01100 | (funct3 << 5) | (funct7 << 8)
+
+# R-type 32-bit instructions: These are mostly binary arithmetic instructions.
+# The encbits are `opcode[6:2] | (funct3 << 5) | (funct7 << 8)
+R = EncRecipe('R', Binary)