diff --git a/lib/cretonne/meta/cdsl/registers.py b/lib/cretonne/meta/cdsl/registers.py
index 6c1d379dac..243a72e669 100644
--- a/lib/cretonne/meta/cdsl/registers.py
+++ b/lib/cretonne/meta/cdsl/registers.py
@@ -19,7 +19,8 @@ The register allocator works with *register classes* which can allocate one or
 more register units at a time. A register class allocates more than one
 register unit at a time when its registers are composed of smaller alocatable
 units. For example, the ARM double precision floating point registers are
-composed of two single precision registers. """
+composed of two single precision registers.
+"""
 from __future__ import absolute_import
 from . import is_power_of_two, next_power_of_two
 
@@ -78,3 +79,53 @@ class RegBank(object):
         # type: () -> str
         return ('RegBank({}, units={}, first_unit={})'
                 .format(self.name, self.units, self.first_unit))
+
+
+class RegClass(object):
+    """
+    A register class is a subset of register units in a RegBank along with a
+    strategy for allocating registers.
+
+    The *width* parameter determines how many register units are allocated at a
+    time. Usually it that is one, but for example the ARM D registers are
+    allocated two units at a time. When multiple units are allocated, it is
+    always a contiguous set of unit numbers.
+
+    :param name: Name of this register class.
+    :param bank: The register bank we're allocating from.
+    :param count: The maximum number of allocations in this register class. By
+                  default, the whole register bank can be allocated.
+    :param width: How many units to allocate at a time.
+    :param start: The first unit to allocate, relative to `bank.first.unit`.
+    :param stride: How many units to skip to get to the next allocation.
+                   Default is `width`.
+    """
+
+    def __init__(self, name, bank, count=None, width=1, start=0, stride=None):
+        # type: (str, RegBank, int, int, int, int) -> None
+        self.name = name
+        self.bank = bank
+        self.start = start
+        self.width = width
+
+        assert width > 0
+        assert start >= 0 and start < bank.units
+
+        if stride is None:
+            stride = width
+        assert stride > 0
+        self.stride = stride
+
+        if count is None:
+            count = bank.units / stride
+        self.count = count
+
+        # When the stride is 1, we can wrap around to the beginning of the
+        # register bank, but with a larger stride, we wouldn't cover all the
+        # possible allocations with a simple modulo stride. For example,
+        # attempting to allocate the even registers before the odd ones
+        # wouldn't work. Only if stride is coprime to bank.units would it work,
+        # but that is unlikely since the bank size is almost always a power of
+        # two.
+        if start + count*stride > bank.units:
+            assert stride == 1, 'Wrapping with stride not supported'
diff --git a/lib/cretonne/meta/isa/arm32/registers.py b/lib/cretonne/meta/isa/arm32/registers.py
index 8d2b0480ae..3084c2bf98 100644
--- a/lib/cretonne/meta/isa/arm32/registers.py
+++ b/lib/cretonne/meta/isa/arm32/registers.py
@@ -2,7 +2,7 @@
 ARM32 register banks.
 """
 from __future__ import absolute_import
-from cdsl.registers import RegBank
+from cdsl.registers import RegBank, RegClass
 from .defs import ISA
 
 
@@ -27,3 +27,8 @@ FloatRegs = RegBank(
         - Q registers are 4 units each.
         """,
         units=64, prefix='s')
+
+GPR = RegClass('GPR', IntRegs)
+S = RegClass('S', FloatRegs, count=32)
+D = RegClass('D', FloatRegs, width=2)
+Q = RegClass('Q', FloatRegs, width=4)
diff --git a/lib/cretonne/meta/isa/arm64/registers.py b/lib/cretonne/meta/isa/arm64/registers.py
index fa1c87120b..fec3601367 100644
--- a/lib/cretonne/meta/isa/arm64/registers.py
+++ b/lib/cretonne/meta/isa/arm64/registers.py
@@ -2,7 +2,7 @@
 Aarch64 register banks.
 """
 from __future__ import absolute_import
-from cdsl.registers import RegBank
+from cdsl.registers import RegBank, RegClass
 from .defs import ISA
 
 
@@ -17,3 +17,6 @@ FloatRegs = RegBank(
         'FloatRegs', ISA,
         'Floating point registers',
         units=32, prefix='v')
+
+GPR = RegClass('GPR', IntRegs)
+FPR = RegClass('FPR', FloatRegs)
diff --git a/lib/cretonne/meta/isa/intel/registers.py b/lib/cretonne/meta/isa/intel/registers.py
index abd6353eb1..6a4c59403e 100644
--- a/lib/cretonne/meta/isa/intel/registers.py
+++ b/lib/cretonne/meta/isa/intel/registers.py
@@ -23,7 +23,7 @@ data types, and the H-registers even less so. Rather than trying to model the
 H-registers accurately, we'll avoid using them in both I32 and I64 modes.
 """
 from __future__ import absolute_import
-from cdsl.registers import RegBank
+from cdsl.registers import RegBank, RegClass
 from .defs import ISA
 
 
@@ -37,3 +37,6 @@ FloatRegs = RegBank(
         'FloatRegs', ISA,
         'SSE floating point registers',
         units=16, prefix='xmm')
+
+GPR = RegClass('GPR', IntRegs)
+FPR = RegClass('FPR', FloatRegs)
diff --git a/lib/cretonne/meta/isa/riscv/registers.py b/lib/cretonne/meta/isa/riscv/registers.py
index 9d1d0eaadb..f00c9a0f0d 100644
--- a/lib/cretonne/meta/isa/riscv/registers.py
+++ b/lib/cretonne/meta/isa/riscv/registers.py
@@ -2,7 +2,7 @@
 RISC-V register banks.
 """
 from __future__ import absolute_import
-from cdsl.registers import RegBank
+from cdsl.registers import RegBank, RegClass
 from .defs import ISA
 
 
@@ -16,3 +16,6 @@ FloatRegs = RegBank(
         'FloatRegs', ISA,
         'Floating point registers',
         units=32, prefix='f')
+
+GPR = RegClass('GPR', IntRegs)
+FPR = RegClass('FPR', FloatRegs)