diff --git a/lib/cretonne/meta/base/formats.py b/lib/cretonne/meta/base/formats.py
index acb9ce0131..6e64e0e3f2 100644
--- a/lib/cretonne/meta/base/formats.py
+++ b/lib/cretonne/meta/base/formats.py
@@ -18,14 +18,10 @@ Unary = InstructionFormat(VALUE)
 UnaryImm = InstructionFormat(imm64)
 UnaryIeee32 = InstructionFormat(ieee32)
 UnaryIeee64 = InstructionFormat(ieee64)
-UnarySplit = InstructionFormat(VALUE, multiple_results=True)
 
 Binary = InstructionFormat(VALUE, VALUE)
 BinaryImm = InstructionFormat(VALUE, imm64)
 
-# Generate result + overflow flag.
-BinaryOverflow = InstructionFormat(VALUE, VALUE, multiple_results=True)
-
 # The select instructions are controlled by the second VALUE operand.
 # The first VALUE operand is the controlling flag which has a derived type.
 # The fma instruction has the same constraint on all inputs.
@@ -33,7 +29,7 @@ Ternary = InstructionFormat(VALUE, VALUE, VALUE, typevar_operand=1)
 
 # Catch-all for instructions with many outputs and inputs and no immediate
 # operands.
-MultiAry = InstructionFormat(VARIABLE_ARGS, multiple_results=True)
+MultiAry = InstructionFormat(VARIABLE_ARGS)
 
 InsertLane = InstructionFormat(VALUE, ('lane', uimm8), VALUE)
 ExtractLane = InstructionFormat(VALUE, ('lane', uimm8))
@@ -47,11 +43,8 @@ Branch = InstructionFormat(VALUE, ebb, VARIABLE_ARGS)
 BranchIcmp = InstructionFormat(intcc, VALUE, VALUE, ebb, VARIABLE_ARGS)
 BranchTable = InstructionFormat(VALUE, jump_table)
 
-Call = InstructionFormat(
-        func_ref, VARIABLE_ARGS, multiple_results=True)
-IndirectCall = InstructionFormat(
-        sig_ref, VALUE, VARIABLE_ARGS,
-        multiple_results=True)
+Call = InstructionFormat(func_ref, VARIABLE_ARGS)
+IndirectCall = InstructionFormat(sig_ref, VALUE, VARIABLE_ARGS)
 
 Load = InstructionFormat(memflags, VALUE, offset32)
 Store = InstructionFormat(memflags, VALUE, VALUE, offset32)
diff --git a/lib/cretonne/meta/cdsl/formats.py b/lib/cretonne/meta/cdsl/formats.py
index f08d6fa119..0b7a72fe0a 100644
--- a/lib/cretonne/meta/cdsl/formats.py
+++ b/lib/cretonne/meta/cdsl/formats.py
@@ -18,13 +18,6 @@ class InstructionFormat(object):
     identified structurally, i.e., the format of an instruction is derived from
     the kinds of operands used in its declaration.
 
-    Most instruction formats produce a single result, or no result at all. If
-    an instruction can produce more than one result, the `multiple_results`
-    flag must be set on its format. All results are of the `value` kind, and
-    the instruction format does not keep track of how many results are
-    produced. Some instructions, like `call`, may have a variable number of
-    results.
-
     The instruction format stores two separate lists of operands: Immediates
     and values. Immediate operands (including entity references) are
     represented as explicit members in the `InstructionData` variants. The
@@ -40,16 +33,14 @@ class InstructionFormat(object):
     :param name: Instruction format name in CamelCase. This is used as a Rust
         variant name in both the `InstructionData` and `InstructionFormat`
         enums.
-    :param multiple_results: Set to `True` if this instruction format allows
-        more than one result to be produced.
     :param typevar_operand: Index of the value input operand that is used to
         infer the controlling type variable. By default, this is `0`, the first
         `value` operand. The index is relative to the values only, ignoring
         immediate operands.
     """
 
-    # Map (multiple_results, imm_kinds, num_value_operands) -> format
-    _registry = dict()  # type: Dict[Tuple[bool, Tuple[OperandKind, ...], int, bool], InstructionFormat]  # noqa
+    # Map (imm_kinds, num_value_operands) -> format
+    _registry = dict()  # type: Dict[Tuple[Tuple[OperandKind, ...], int, bool], InstructionFormat]  # noqa
 
     # All existing formats.
     all_formats = list()  # type: List[InstructionFormat]
@@ -57,7 +48,6 @@ class InstructionFormat(object):
     def __init__(self, *kinds, **kwargs):
         # type: (*Union[OperandKind, Tuple[str, OperandKind]], **Any) -> None # noqa
         self.name = kwargs.get('name', None)  # type: str
-        self.multiple_results = kwargs.get('multiple_results', False)
 
         # The number of value operands stored in the format, or `None` when
         # `has_value_list` is set.
@@ -81,9 +71,7 @@ class InstructionFormat(object):
 
         # Compute a signature for the global registry.
         imm_kinds = tuple(f.kind for f in self.imm_fields)
-        sig = (
-                self.multiple_results, imm_kinds, self.num_value_operands,
-                self.has_value_list)
+        sig = (imm_kinds, self.num_value_operands, self.has_value_list)
         if sig in InstructionFormat._registry:
             raise RuntimeError(
                 "Format '{}' has the same signature as existing format '{}'"
@@ -158,37 +146,24 @@ class InstructionFormat(object):
         :py:class:`Instruction` arguments of the same name, except they must be
         tuples of :py:`Operand` objects.
         """
-        if len(outs) == 1:
-            multiple_results = outs[0].kind == VARIABLE_ARGS
-        else:
-            multiple_results = len(outs) > 1
-
         # Construct a signature.
         imm_kinds = tuple(op.kind for op in ins if op.is_immediate())
         num_values = sum(1 for op in ins if op.is_value())
         has_varargs = (VARIABLE_ARGS in tuple(op.kind for op in ins))
 
-        sig = (multiple_results, imm_kinds, num_values, has_varargs)
+        sig = (imm_kinds, num_values, has_varargs)
         if sig in InstructionFormat._registry:
             return InstructionFormat._registry[sig]
 
         # Try another value list format as an alternative.
-        sig = (True, imm_kinds, num_values, has_varargs)
-        if sig in InstructionFormat._registry:
-            return InstructionFormat._registry[sig]
-
-        sig = (multiple_results, imm_kinds, 0, True)
-        if sig in InstructionFormat._registry:
-            return InstructionFormat._registry[sig]
-
-        sig = (True, imm_kinds, 0, True)
+        sig = (imm_kinds, 0, True)
         if sig in InstructionFormat._registry:
             return InstructionFormat._registry[sig]
 
         raise RuntimeError(
-                'No instruction format matches multiple_results={},'
+                'No instruction format matches '
                 'imms={}, vals={}, varargs={}'.format(
-                    multiple_results, imm_kinds, num_values, has_varargs))
+                    imm_kinds, num_values, has_varargs))
 
     @staticmethod
     def extract_names(globs):
diff --git a/lib/cretonne/meta/cdsl/isa.py b/lib/cretonne/meta/cdsl/isa.py
index 1ead583c5a..a44a1e6333 100644
--- a/lib/cretonne/meta/cdsl/isa.py
+++ b/lib/cretonne/meta/cdsl/isa.py
@@ -207,8 +207,6 @@ class EncRecipe(object):
         if not format.has_value_list:
             assert len(self.ins) == format.num_value_operands
         self.outs = self._verify_constraints(outs)
-        if len(self.outs) > 1:
-            assert format.multiple_results
 
     def __str__(self):
         # type: () -> str
diff --git a/lib/cretonne/src/ir/instructions.rs b/lib/cretonne/src/ir/instructions.rs
index 61ed2f1eeb..9484110d83 100644
--- a/lib/cretonne/src/ir/instructions.rs
+++ b/lib/cretonne/src/ir/instructions.rs
@@ -105,14 +105,12 @@ pub enum InstructionData {
     UnaryImm { opcode: Opcode, imm: Imm64 },
     UnaryIeee32 { opcode: Opcode, imm: Ieee32 },
     UnaryIeee64 { opcode: Opcode, imm: Ieee64 },
-    UnarySplit { opcode: Opcode, arg: Value },
     Binary { opcode: Opcode, args: [Value; 2] },
     BinaryImm {
         opcode: Opcode,
         arg: Value,
         imm: Imm64,
     },
-    BinaryOverflow { opcode: Opcode, args: [Value; 2] },
     Ternary { opcode: Opcode, args: [Value; 3] },
     MultiAry { opcode: Opcode, args: ValueList },
     InsertLane {
diff --git a/lib/cretonne/src/verifier.rs b/lib/cretonne/src/verifier.rs
index ba2f03ec9d..ee78a07501 100644
--- a/lib/cretonne/src/verifier.rs
+++ b/lib/cretonne/src/verifier.rs
@@ -255,10 +255,8 @@ impl<'a> Verifier<'a> {
             &UnaryImm { .. } |
             &UnaryIeee32 { .. } |
             &UnaryIeee64 { .. } |
-            &UnarySplit { .. } |
             &Binary { .. } |
             &BinaryImm { .. } |
-            &BinaryOverflow { .. } |
             &Ternary { .. } |
             &InsertLane { .. } |
             &ExtractLane { .. } |
diff --git a/lib/cretonne/src/write.rs b/lib/cretonne/src/write.rs
index 09e5ee6641..fcfb843c0c 100644
--- a/lib/cretonne/src/write.rs
+++ b/lib/cretonne/src/write.rs
@@ -245,10 +245,8 @@ pub fn write_operands(w: &mut Write, dfg: &DataFlowGraph, inst: Inst) -> Result
         UnaryImm { imm, .. } => write!(w, " {}", imm),
         UnaryIeee32 { imm, .. } => write!(w, " {}", imm),
         UnaryIeee64 { imm, .. } => write!(w, " {}", imm),
-        UnarySplit { arg, .. } => write!(w, " {}", arg),
         Binary { args, .. } => write!(w, " {}, {}", args[0], args[1]),
         BinaryImm { arg, imm, .. } => write!(w, " {}, {}", arg, imm),
-        BinaryOverflow { args, .. } => write!(w, " {}, {}", args[0], args[1]),
         Ternary { args, .. } => write!(w, " {}, {}, {}", args[0], args[1], args[2]),
         MultiAry { ref args, .. } => {
             if args.is_empty() {
diff --git a/lib/reader/src/parser.rs b/lib/reader/src/parser.rs
index ac2754a46c..f133732e8e 100644
--- a/lib/reader/src/parser.rs
+++ b/lib/reader/src/parser.rs
@@ -1429,12 +1429,6 @@ impl<'a> Parser<'a> {
                     imm: self.match_ieee64("expected immediate 64-bit float operand")?,
                 }
             }
-            InstructionFormat::UnarySplit => {
-                InstructionData::UnarySplit {
-                    opcode: opcode,
-                    arg: self.match_value("expected SSA value operand")?,
-                }
-            }
             InstructionFormat::Binary => {
                 let lhs = self.match_value("expected SSA value first operand")?;
                 self.match_token(Token::Comma, "expected ',' between operands")?;
@@ -1454,15 +1448,6 @@ impl<'a> Parser<'a> {
                     imm: rhs,
                 }
             }
-            InstructionFormat::BinaryOverflow => {
-                let lhs = self.match_value("expected SSA value first operand")?;
-                self.match_token(Token::Comma, "expected ',' between operands")?;
-                let rhs = self.match_value("expected SSA value second operand")?;
-                InstructionData::BinaryOverflow {
-                    opcode: opcode,
-                    args: [lhs, rhs],
-                }
-            }
             InstructionFormat::Ternary => {
                 // Names here refer to the `select` instruction.
                 // This format is also use by `fma`.