diff --git a/docs/langref.rst b/docs/langref.rst
index 008f2a74b1..e6a0e2b3d5 100644
--- a/docs/langref.rst
+++ b/docs/langref.rst
@@ -583,6 +583,11 @@ allocation pass and beyond.
 .. autoinst:: spill
 .. autoinst:: fill
 
+Register values can be temporarily diverted to other registers by the
+:inst:`regmove` instruction.
+
+.. autoinst:: regmove
+
 Vector operations
 -----------------
 
diff --git a/filetests/parser/tiny.cton b/filetests/parser/tiny.cton
index 87140d9aad..5ad2f7a39d 100644
--- a/filetests/parser/tiny.cton
+++ b/filetests/parser/tiny.cton
@@ -155,3 +155,18 @@ ebb0(v1: i32):
 ; nextln:     store $v2, $v1
 ; nextln:     store aligned $v3, $v1+12
 ; nextln:     store notrap aligned $v3, $v1-12
+
+; Register diversions.
+; This test file has no ISA, so we can unly use register unit numbers.
+function diversion(i32) {
+ebb0(v1: i32):
+    regmove v1, %10 -> %20
+    regmove v1, %20 -> %10
+    return
+}
+; sameln: function diversion(i32) {
+; nextln: ebb0($v1: i32):
+; nextln:     regmove $v1, %10 -> %20
+; nextln:     regmove $v1, %20 -> %10
+; nextln:     return
+; nextln: }
diff --git a/lib/cretonne/meta/base/formats.py b/lib/cretonne/meta/base/formats.py
index 6e64e0e3f2..368fb13078 100644
--- a/lib/cretonne/meta/base/formats.py
+++ b/lib/cretonne/meta/base/formats.py
@@ -9,7 +9,7 @@ from __future__ import absolute_import
 from cdsl.formats import InstructionFormat
 from cdsl.operands import VALUE, VARIABLE_ARGS
 from .immediates import imm64, uimm8, ieee32, ieee64, offset32, uoffset32
-from .immediates import intcc, floatcc, memflags
+from .immediates import intcc, floatcc, memflags, regunit
 from .entities import ebb, sig_ref, func_ref, jump_table, stack_slot
 
 Nullary = InstructionFormat()
@@ -57,5 +57,7 @@ StackStore = InstructionFormat(VALUE, stack_slot, offset32)
 HeapLoad = InstructionFormat(VALUE, uoffset32)
 HeapStore = InstructionFormat(VALUE, VALUE, uoffset32)
 
+RegMove = InstructionFormat(VALUE, ('src', regunit), ('dst', regunit))
+
 # Finally extract the names of global variables in this module.
 InstructionFormat.extract_names(globals())
diff --git a/lib/cretonne/meta/base/immediates.py b/lib/cretonne/meta/base/immediates.py
index 8e643bb9ee..2458b76e70 100644
--- a/lib/cretonne/meta/base/immediates.py
+++ b/lib/cretonne/meta/base/immediates.py
@@ -96,3 +96,9 @@ memflags = ImmediateKind(
         'memflags',
         'Memory operation flags',
         default_member='flags', rust_type='MemFlags')
+
+#: A register unit in the current target ISA.
+regunit = ImmediateKind(
+        'regunit',
+        'A register unit in the target ISA',
+        rust_type='RegUnit')
diff --git a/lib/cretonne/meta/base/instructions.py b/lib/cretonne/meta/base/instructions.py
index 3035f2b98e..b9d2d5a5af 100644
--- a/lib/cretonne/meta/base/instructions.py
+++ b/lib/cretonne/meta/base/instructions.py
@@ -10,7 +10,7 @@ from cdsl.typevar import TypeVar
 from cdsl.instructions import Instruction, InstructionGroup
 from base.types import i8, f32, f64, b1
 from base.immediates import imm64, uimm8, ieee32, ieee64, offset32, uoffset32
-from base.immediates import intcc, floatcc, memflags
+from base.immediates import intcc, floatcc, memflags, regunit
 from base import entities
 import base.formats  # noqa
 
@@ -467,6 +467,23 @@ fill = Instruction(
         """,
         ins=x, outs=a)
 
+src = Operand('src', regunit)
+dst = Operand('dst', regunit)
+
+regmove = Instruction(
+        'regmove', r"""
+        Temporarily divert ``x`` from ``src`` to ``dst``.
+
+        This instruction moves the location of a value from one register to
+        another without creating a new SSA value. It is used by the register
+        allocator to temporarily rearrange register assignments in order to
+        satisfy instruction constraints.
+
+        The register diversions created by this instruction must be undone
+        before the value leaves the EBB. At the entry to a new EBB, all live
+        values must be in their originally assigned registers.
+        """,
+        ins=(x, src, dst))
 
 #
 # Vector operations
diff --git a/lib/cretonne/src/ir/builder.rs b/lib/cretonne/src/ir/builder.rs
index ae71f754c7..a5a3719299 100644
--- a/lib/cretonne/src/ir/builder.rs
+++ b/lib/cretonne/src/ir/builder.rs
@@ -9,6 +9,7 @@ use ir::{Opcode, Type, Inst, Value, Ebb, JumpTable, SigRef, FuncRef, StackSlot,
          MemFlags};
 use ir::immediates::{Imm64, Uimm8, Ieee32, Ieee64, Offset32, Uoffset32};
 use ir::condcodes::{IntCC, FloatCC};
+use isa::RegUnit;
 
 /// Base trait for instruction builders.
 ///
diff --git a/lib/cretonne/src/ir/dfg.rs b/lib/cretonne/src/ir/dfg.rs
index 063d7cbbd7..6e33c9d592 100644
--- a/lib/cretonne/src/ir/dfg.rs
+++ b/lib/cretonne/src/ir/dfg.rs
@@ -687,7 +687,7 @@ impl<'a> fmt::Display for DisplayInst<'a> {
         } else {
             write!(f, "{}.{}", inst.opcode(), typevar)?;
         }
-        write_operands(f, dfg, self.1)
+        write_operands(f, dfg, None, self.1)
     }
 }
 
diff --git a/lib/cretonne/src/ir/instructions.rs b/lib/cretonne/src/ir/instructions.rs
index 9484110d83..0b32929af6 100644
--- a/lib/cretonne/src/ir/instructions.rs
+++ b/lib/cretonne/src/ir/instructions.rs
@@ -14,6 +14,7 @@ use ir::{Value, Type, Ebb, JumpTable, SigRef, FuncRef, StackSlot, MemFlags};
 use ir::immediates::{Imm64, Uimm8, Ieee32, Ieee64, Offset32, Uoffset32};
 use ir::condcodes::*;
 use ir::types;
+use isa::RegUnit;
 
 use entity_list;
 use ref_slice::{ref_slice, ref_slice_mut};
@@ -203,6 +204,12 @@ pub enum InstructionData {
         args: [Value; 2],
         offset: Offset32,
     },
+    RegMove {
+        opcode: Opcode,
+        arg: Value,
+        src: RegUnit,
+        dst: RegUnit,
+    },
 }
 
 /// A variable list of `Value` operands used for function call arguments and passing arguments to
diff --git a/lib/cretonne/src/verifier/mod.rs b/lib/cretonne/src/verifier/mod.rs
index 82e95d7f1f..e1568d5bab 100644
--- a/lib/cretonne/src/verifier/mod.rs
+++ b/lib/cretonne/src/verifier/mod.rs
@@ -284,7 +284,8 @@ impl<'a> Verifier<'a> {
             &HeapLoad { .. } |
             &HeapStore { .. } |
             &Load { .. } |
-            &Store { .. } => {}
+            &Store { .. } |
+            &RegMove { .. } => {}
         }
 
         Ok(())
diff --git a/lib/cretonne/src/write.rs b/lib/cretonne/src/write.rs
index 5d46ccb624..af66cc8868 100644
--- a/lib/cretonne/src/write.rs
+++ b/lib/cretonne/src/write.rs
@@ -225,12 +225,16 @@ fn write_instruction(w: &mut Write,
         None => write!(w, "{}", opcode)?,
     }
 
-    write_operands(w, &func.dfg, inst)?;
+    write_operands(w, &func.dfg, isa, inst)?;
     writeln!(w, "")
 }
 
 /// Write the operands of `inst` to `w` with a prepended space.
-pub fn write_operands(w: &mut Write, dfg: &DataFlowGraph, inst: Inst) -> Result {
+pub fn write_operands(w: &mut Write,
+                      dfg: &DataFlowGraph,
+                      isa: Option<&TargetIsa>,
+                      inst: Inst)
+                      -> Result {
     let pool = &dfg.value_lists;
     use ir::instructions::InstructionData::*;
     match dfg[inst] {
@@ -321,6 +325,19 @@ pub fn write_operands(w: &mut Write, dfg: &DataFlowGraph, inst: Inst) -> Result
             offset,
             ..
         } => write!(w, "{} {}, {}{}", flags, args[0], args[1], offset),
+        RegMove { arg, src, dst, .. } => {
+            if let Some(isa) = isa {
+                let regs = isa.register_info();
+                write!(w,
+                       " {}, {} -> {}",
+                       arg,
+                       regs.display_regunit(src),
+                       regs.display_regunit(dst))
+            } else {
+                write!(w, " {}, %{} -> %{}", arg, src, dst)
+            }
+        }
+
     }
 }
 
diff --git a/lib/reader/src/parser.rs b/lib/reader/src/parser.rs
index 02ec88196e..b907ee426f 100644
--- a/lib/reader/src/parser.rs
+++ b/lib/reader/src/parser.rs
@@ -16,7 +16,7 @@ use cretonne::ir::types::VOID;
 use cretonne::ir::immediates::{Imm64, Offset32, Uoffset32, Ieee32, Ieee64};
 use cretonne::ir::entities::AnyEntity;
 use cretonne::ir::instructions::{InstructionFormat, InstructionData, VariableArgs};
-use cretonne::isa::{self, TargetIsa, Encoding};
+use cretonne::isa::{self, TargetIsa, Encoding, RegUnit};
 use cretonne::settings::{self, Configurable};
 use testfile::{TestFile, Details, Comment};
 use error::{Location, Error, Result};
@@ -551,6 +551,29 @@ impl<'a> Parser<'a> {
         }
     }
 
+    // Match and consume a register unit either by number `%15` or by name `%rax`.
+    fn match_regunit(&mut self, isa: Option<&TargetIsa>) -> Result<RegUnit> {
+        if let Some(Token::Name(name)) = self.token() {
+            self.consume();
+            match isa {
+                Some(isa) => {
+                    isa.register_info()
+                        .parse_regunit(name)
+                        .ok_or_else(|| self.error("invalid register name"))
+                }
+                None => {
+                    name.parse()
+                        .map_err(|_| self.error("invalid register number"))
+                }
+            }
+        } else {
+            match isa {
+                Some(isa) => err!(self.loc, "Expected {} register unit", isa.name()),
+                None => err!(self.loc, "Expected register unit number"),
+            }
+        }
+    }
+
     /// Parse a list of test commands.
     pub fn parse_test_commands(&mut self) -> Vec<TestCommand<'a>> {
         let mut list = Vec::new();
@@ -1664,6 +1687,19 @@ impl<'a> Parser<'a> {
                     offset,
                 }
             }
+            InstructionFormat::RegMove => {
+                let arg = self.match_value("expected SSA value operand")?;
+                self.match_token(Token::Comma, "expected ',' between operands")?;
+                let src = self.match_regunit(ctx.unique_isa)?;
+                self.match_token(Token::Arrow, "expected '->' between register units")?;
+                let dst = self.match_regunit(ctx.unique_isa)?;
+                InstructionData::RegMove {
+                    opcode,
+                    arg,
+                    src,
+                    dst,
+                }
+            }
         };
         Ok(idata)
     }