diff --git a/cranelift/codegen/meta/src/gen_inst.rs b/cranelift/codegen/meta/src/gen_inst.rs
index c975cef961..a93538ca3f 100644
--- a/cranelift/codegen/meta/src/gen_inst.rs
+++ b/cranelift/codegen/meta/src/gen_inst.rs
@@ -665,7 +665,7 @@ fn typeset_to_string(ts: &TypeSet) -> String {
 }
 
 /// Generate the table of ValueTypeSets described by type_sets.
-fn gen_typesets_table(type_sets: &UniqueTable<TypeSet>, fmt: &mut Formatter) {
+pub fn gen_typesets_table(type_sets: &UniqueTable<TypeSet>, fmt: &mut Formatter) {
     if type_sets.len() == 0 {
         return;
     }
diff --git a/cranelift/codegen/meta/src/gen_legalizer.rs b/cranelift/codegen/meta/src/gen_legalizer.rs
new file mode 100644
index 0000000000..de7a8068b9
--- /dev/null
+++ b/cranelift/codegen/meta/src/gen_legalizer.rs
@@ -0,0 +1,578 @@
+use crate::cdsl::ast::{Def, DefPool, VarPool};
+use crate::cdsl::formats::FormatRegistry;
+use crate::cdsl::isa::TargetIsa;
+use crate::cdsl::type_inference::Constraint;
+use crate::cdsl::typevar::{TypeSet, TypeVar};
+use crate::cdsl::xform::{Transform, TransformGroup, TransformGroups};
+
+use crate::error;
+use crate::gen_inst::gen_typesets_table;
+use crate::srcgen::Formatter;
+use crate::unique_table::UniqueTable;
+
+use std::collections::{HashMap, HashSet};
+use std::iter::FromIterator;
+
+/// Given a `Def` node, emit code that extracts all the instruction fields from
+/// `pos.func.dfg[iref]`.
+///
+/// Create local variables named after the `Var` instances in `node`.
+///
+/// Also create a local variable named `predicate` with the value of the evaluated instruction
+/// predicate, or `true` if the node has no predicate.
+fn unwrap_inst(
+    transform: &Transform,
+    format_registry: &FormatRegistry,
+    fmt: &mut Formatter,
+) -> bool {
+    let var_pool = &transform.var_pool;
+    let def_pool = &transform.def_pool;
+
+    let def = def_pool.get(transform.src);
+    let apply = &def.apply;
+    let inst = &apply.inst;
+    let iform = format_registry.get(inst.format);
+
+    fmt.comment(format!(
+        "Unwrap {}",
+        def.to_comment_string(&transform.var_pool)
+    ));
+
+    // Extract the Var arguments.
+    let arg_names = apply
+        .args
+        .iter()
+        .map(|arg| match arg.maybe_var() {
+            Some(var_index) => var_pool.get(var_index).name,
+            None => "_",
+        })
+        .collect::<Vec<_>>()
+        .join(", ");
+
+    fmtln!(
+        fmt,
+        "let ({}, predicate) = if let crate::ir::InstructionData::{} {{",
+        arg_names,
+        iform.name
+    );
+    fmt.indent(|fmt| {
+        // Fields are encoded directly.
+        for field in &iform.imm_fields {
+            fmtln!(fmt, "{},", field.member);
+        }
+
+        if iform.num_value_operands == 1 {
+            fmt.line("arg,");
+        } else if iform.has_value_list || iform.num_value_operands > 1 {
+            fmt.line("ref args,");
+        }
+
+        fmt.line("..");
+        fmt.outdented_line("} = pos.func.dfg[inst] {");
+        fmt.line("let func = &pos.func;");
+
+        if iform.has_value_list {
+            fmt.line("let args = args.as_slice(&func.dfg.value_lists);");
+        } else if iform.num_value_operands == 1 {
+            fmt.line("let args = [arg];")
+        }
+
+        // Generate the values for the tuple.
+        fmt.line("(");
+        fmt.indent(|fmt| {
+            for (op_num, op) in inst.operands_in.iter().enumerate() {
+                if op.is_immediate() {
+                    let n = inst.imm_opnums.iter().position(|&i| i == op_num).unwrap();
+                    fmtln!(fmt, "{},", iform.imm_fields[n].member);
+                } else if op.is_value() {
+                    let n = inst.value_opnums.iter().position(|&i| i == op_num).unwrap();
+                    fmtln!(fmt, "func.dfg.resolve_aliases(args[{}]),", n);
+                }
+            }
+
+            // Evaluate the instruction predicate if any.
+            fmt.multi_line(
+                &apply
+                    .inst_predicate_with_ctrl_typevar(format_registry, var_pool)
+                    .rust_predicate(),
+            );
+        });
+        fmt.line(")");
+
+        fmt.outdented_line("} else {");
+        fmt.line(r#"unreachable!("bad instruction format")"#);
+    });
+    fmtln!(fmt, "};");
+
+    for &op_num in &inst.value_opnums {
+        let arg = &apply.args[op_num];
+        if let Some(var_index) = arg.maybe_var() {
+            let var = var_pool.get(var_index);
+            if var.has_free_typevar() {
+                fmtln!(
+                    fmt,
+                    "let typeof_{} = pos.func.dfg.value_type({});",
+                    var.name,
+                    var.name
+                );
+            }
+        }
+    }
+
+    // If the definition creates results, detach the values and place them in locals.
+    let mut replace_inst = false;
+    if def.defined_vars.len() > 0 {
+        if def.defined_vars
+            == def_pool
+                .get(var_pool.get(def.defined_vars[0]).dst_def.unwrap())
+                .defined_vars
+        {
+            // Special case: The instruction replacing node defines the exact same values.
+            fmt.comment(format!(
+                "Results handled by {}.",
+                def_pool
+                    .get(var_pool.get(def.defined_vars[0]).dst_def.unwrap())
+                    .to_comment_string(var_pool)
+            ));
+            replace_inst = true;
+        } else {
+            // Boring case: Detach the result values, capture them in locals.
+            for &var_index in &def.defined_vars {
+                fmtln!(fmt, "let {};", var_pool.get(var_index).name);
+            }
+
+            fmt.line("{");
+            fmt.indent(|fmt| {
+                fmt.line("let r = pos.func.dfg.inst_results(inst);");
+                for i in 0..def.defined_vars.len() {
+                    let var = var_pool.get(def.defined_vars[i]);
+                    fmtln!(fmt, "{} = r[{}];", var.name, i);
+                }
+            });
+            fmt.line("}");
+
+            for &var_index in &def.defined_vars {
+                let var = var_pool.get(var_index);
+                if var.has_free_typevar() {
+                    fmtln!(
+                        fmt,
+                        "let typeof_{} = pos.func.dfg.value_type({});",
+                        var.name,
+                        var.name
+                    );
+                }
+            }
+        }
+    }
+    replace_inst
+}
+
+fn build_derived_expr(tv: &TypeVar) -> String {
+    let base = match &tv.base {
+        Some(base) => base,
+        None => {
+            assert!(tv.name.starts_with("typeof_"));
+            return format!("Some({})", tv.name);
+        }
+    };
+    let base_expr = build_derived_expr(&base.type_var);
+    format!(
+        "{}.map(|t: crate::ir::Type| t.{}())",
+        base_expr,
+        base.derived_func.name()
+    )
+}
+
+/// Emit rust code for the given check.
+///
+/// The emitted code is a statement redefining the `predicate` variable like this:
+///     let predicate = predicate && ...
+fn emit_runtime_typecheck<'a, 'b>(
+    constraint: &'a Constraint,
+    type_sets: &mut UniqueTable<'a, TypeSet>,
+    fmt: &mut Formatter,
+) {
+    match constraint {
+        Constraint::InTypeset(tv, ts) => {
+            let ts_index = type_sets.add(&ts);
+            fmt.comment(format!(
+                "{} must belong to {:?}",
+                tv.name,
+                type_sets.get(ts_index)
+            ));
+            fmtln!(
+                fmt,
+                "let predicate = predicate && TYPE_SETS[{}].contains({});",
+                ts_index,
+                tv.name
+            );
+        }
+        Constraint::Eq(tv1, tv2) => {
+            fmtln!(
+                fmt,
+                "let predicate = predicate && match ({}, {}) {{",
+                build_derived_expr(tv1),
+                build_derived_expr(tv2)
+            );
+            fmt.indent(|fmt| {
+                fmt.line("(Some(a), Some(b)) => a == b,");
+                fmt.comment("On overflow, constraint doesn\'t apply");
+                fmt.line("_ => false,");
+            });
+            fmtln!(fmt, "};");
+        }
+        Constraint::WiderOrEq(tv1, tv2) => {
+            fmtln!(
+                fmt,
+                "let predicate = predicate && match ({}, {}) {{",
+                build_derived_expr(tv1),
+                build_derived_expr(tv2)
+            );
+            fmt.indent(|fmt| {
+                fmt.line("(Some(a), Some(b)) => a.wider_or_equal(b),");
+                fmt.comment("On overflow, constraint doesn\'t apply");
+                fmt.line("_ => false,");
+            });
+            fmtln!(fmt, "};");
+        }
+    }
+}
+
+/// Determine if `node` represents one of the value splitting instructions: `isplit` or `vsplit.
+/// These instructions are lowered specially by the `legalize::split` module.
+fn is_value_split(def: &Def) -> bool {
+    let name = def.apply.inst.name;
+    name == "isplit" || name == "vsplit"
+}
+
+fn emit_dst_inst(def: &Def, def_pool: &DefPool, var_pool: &VarPool, fmt: &mut Formatter) {
+    let defined_vars = {
+        let vars = def
+            .defined_vars
+            .iter()
+            .map(|&var_index| var_pool.get(var_index).name)
+            .collect::<Vec<_>>();
+        if vars.len() == 1 {
+            vars[0].to_string()
+        } else {
+            format!("({})", vars.join(", "))
+        }
+    };
+
+    if is_value_split(def) {
+        // Split instructions are not emitted with the builder, but by calling special functions in
+        // the `legalizer::split` module. These functions will eliminate concat-split patterns.
+        fmt.line("let curpos = pos.position();");
+        fmt.line("let srcloc = pos.srcloc();");
+        fmtln!(
+            fmt,
+            "let {} = split::{}(pos.func, cfg, curpos, srcloc, {});",
+            defined_vars,
+            def.apply.inst.snake_name(),
+            def.apply.args[0].to_rust_code(var_pool)
+        );
+        return;
+    }
+
+    if def.defined_vars.is_empty() {
+        // This node doesn't define any values, so just insert the new instruction.
+        fmtln!(
+            fmt,
+            "pos.ins().{};",
+            def.apply.rust_builder(&def.defined_vars, var_pool)
+        );
+        return;
+    }
+
+    if let Some(src_def0) = var_pool.get(def.defined_vars[0]).src_def {
+        if def.defined_vars == def_pool.get(src_def0).defined_vars {
+            // The replacement instruction defines the exact same values as the source pattern.
+            // Unwrapping would have left the results intact.  Replace the whole instruction.
+            fmtln!(
+                fmt,
+                "let {} = pos.func.dfg.replace(inst).{};",
+                defined_vars,
+                def.apply.rust_builder(&def.defined_vars, var_pool)
+            );
+
+            // We need to bump the cursor so following instructions are inserted *after* the
+            // replaced instruction.
+            fmt.line("if pos.current_inst() == Some(inst) {");
+            fmt.indent(|fmt| {
+                fmt.line("pos.next_inst();");
+            });
+            fmt.line("}");
+            return;
+        }
+    }
+
+    // Insert a new instruction.
+    let mut builder = format!("let {} = pos.ins()", defined_vars);
+
+    if def.defined_vars.len() == 1 && var_pool.get(def.defined_vars[0]).is_output() {
+        // Reuse the single source result value.
+        builder = format!(
+            "{}.with_result({})",
+            builder,
+            var_pool.get(def.defined_vars[0]).to_rust_code()
+        );
+    } else if def
+        .defined_vars
+        .iter()
+        .any(|&var_index| var_pool.get(var_index).is_output())
+    {
+        // There are more than one output values that can be reused.
+        let array = def
+            .defined_vars
+            .iter()
+            .map(|&var_index| {
+                let var = var_pool.get(var_index);
+                if var.is_output() {
+                    format!("Some({})", var.name)
+                } else {
+                    "None".into()
+                }
+            })
+            .collect::<Vec<_>>()
+            .join(", ");
+        builder = format!("{}.with_results([{}])", builder, array);
+    }
+
+    fmtln!(
+        fmt,
+        "{}.{};",
+        builder,
+        def.apply.rust_builder(&def.defined_vars, var_pool)
+    );
+}
+
+/// Emit code for `transform`, assuming that the opcode of transform's root instruction
+/// has already been matched.
+///
+/// `inst: Inst` is the variable to be replaced. It is pointed to by `pos: Cursor`.
+/// `dfg: DataFlowGraph` is available and mutable.
+fn gen_transform<'a>(
+    transform: &'a Transform,
+    format_registry: &FormatRegistry,
+    type_sets: &mut UniqueTable<'a, TypeSet>,
+    fmt: &mut Formatter,
+) {
+    // Unwrap the source instruction, create local variables for the input variables.
+    let replace_inst = unwrap_inst(&transform, format_registry, fmt);
+
+    // Emit any runtime checks; these will rebind `predicate` emitted by unwrap_inst().
+    for constraint in &transform.type_env.constraints {
+        emit_runtime_typecheck(constraint, type_sets, fmt);
+    }
+
+    // Guard the actual expansion by `predicate`.
+    fmt.line("if predicate {");
+    fmt.indent(|fmt| {
+        // If we're going to delete `inst`, we need to detach its results first so they can be
+        // reattached during pattern expansion.
+        if !replace_inst {
+            fmt.line("pos.func.dfg.clear_results(inst);");
+        }
+
+        // Emit the destination pattern.
+        for &def_index in &transform.dst {
+            emit_dst_inst(
+                transform.def_pool.get(def_index),
+                &transform.def_pool,
+                &transform.var_pool,
+                fmt,
+            );
+        }
+
+        // Delete the original instruction if we didn't have an opportunity to replace it.
+        if !replace_inst {
+            fmt.line("let removed = pos.remove_inst();");
+            fmt.line("debug_assert_eq!(removed, inst);");
+        }
+        fmt.line("return true;");
+    });
+    fmt.line("}");
+}
+
+fn gen_transform_group<'a>(
+    group: &'a TransformGroup,
+    format_registry: &FormatRegistry,
+    transform_groups: &TransformGroups,
+    type_sets: &mut UniqueTable<'a, TypeSet>,
+    fmt: &mut Formatter,
+) {
+    fmt.doc_comment(group.doc);
+    fmt.line("#[allow(unused_variables,unused_assignments,non_snake_case)]");
+
+    // Function arguments.
+    fmtln!(fmt, "pub fn {}(", group.name);
+    fmt.indent(|fmt| {
+        fmt.line("inst: crate::ir::Inst,");
+        fmt.line("func: &mut crate::ir::Function,");
+        fmt.line("cfg: &mut crate::flowgraph::ControlFlowGraph,");
+        fmt.line("isa: &crate::isa::TargetIsa,");
+    });
+    fmtln!(fmt, ") -> bool {");
+
+    // Function body.
+    fmt.indent(|fmt| {
+        fmt.line("use crate::ir::InstBuilder;");
+        fmt.line("use crate::cursor::{Cursor, FuncCursor};");
+        fmt.line("let mut pos = FuncCursor::new(func).at_inst(inst);");
+        fmt.line("pos.use_srcloc(inst);");
+
+        // Group the transforms by opcode so we can generate a big switch.
+        // Preserve ordering.
+        let mut inst_to_transforms = HashMap::new();
+        for transform in &group.transforms {
+            let def_index = transform.src;
+            let inst = &transform.def_pool.get(def_index).apply.inst;
+            inst_to_transforms
+                .entry(inst.camel_name.clone())
+                .or_insert(Vec::new())
+                .push(transform);
+        }
+
+        let mut sorted_inst_names = Vec::from_iter(inst_to_transforms.keys());
+        sorted_inst_names.sort();
+
+        fmt.line("{");
+        fmt.indent(|fmt| {
+            fmt.line("match pos.func.dfg[inst].opcode() {");
+            fmt.indent(|fmt| {
+                for camel_name in sorted_inst_names {
+                    fmtln!(fmt, "ir::Opcode::{} => {{", camel_name);
+                    fmt.indent(|fmt| {
+                        for transform in inst_to_transforms.get(camel_name).unwrap() {
+                            gen_transform(transform, format_registry, type_sets, fmt);
+                        }
+                    });
+                    fmtln!(fmt, "}");
+                    fmt.empty_line();
+                }
+
+                // Emit the custom transforms. The Rust compiler will complain about any overlap with
+                // the normal transforms.
+                for (inst_camel_name, func_name) in &group.custom_legalizes {
+                    fmtln!(fmt, "ir::Opcode::{} => {{", inst_camel_name);
+                    fmt.indent(|fmt| {
+                        fmtln!(fmt, "{}(inst, pos.func, cfg, isa);", func_name);
+                        fmt.line("return true;");
+                    });
+                    fmtln!(fmt, "}");
+                    fmt.empty_line();
+                }
+
+                // We'll assume there are uncovered opcodes.
+                fmt.line("_ => {},");
+            });
+            fmt.line("}");
+        });
+        fmt.line("}");
+
+        // If we fall through, nothing was expanded; call the chain if any.
+        match &group.chain_with {
+            Some(group_id) => fmtln!(
+                fmt,
+                "{}(inst, pos.func, cfg, isa)",
+                transform_groups.get(*group_id).rust_name()
+            ),
+            None => fmt.line("false"),
+        };
+    });
+    fmtln!(fmt, "}");
+    fmt.empty_line();
+}
+
+/// Generate legalization functions for `isa` and add any shared `TransformGroup`s
+/// encountered to `shared_groups`.
+///
+/// Generate `TYPE_SETS` and `LEGALIZE_ACTIONS` tables.
+fn gen_isa(
+    isa: &TargetIsa,
+    format_registry: &FormatRegistry,
+    transform_groups: &TransformGroups,
+    shared_group_names: &mut HashSet<&'static str>,
+    fmt: &mut Formatter,
+) {
+    let mut type_sets = UniqueTable::new();
+    for group_index in isa.transitive_transform_groups(transform_groups) {
+        let group = transform_groups.get(group_index);
+        match group.isa_name {
+            Some(isa_name) => {
+                assert!(
+                    isa_name == isa.name,
+                    "ISA-specific legalizations must be used by the same ISA"
+                );
+                gen_transform_group(
+                    group,
+                    format_registry,
+                    transform_groups,
+                    &mut type_sets,
+                    fmt,
+                );
+            }
+            None => {
+                shared_group_names.insert(group.name);
+            }
+        }
+    }
+
+    gen_typesets_table(&type_sets, fmt);
+
+    let direct_groups = isa.direct_transform_groups();
+    fmtln!(
+        fmt,
+        "pub static LEGALIZE_ACTIONS: [isa::Legalize; {}] = [",
+        direct_groups.len()
+    );
+    fmt.indent(|fmt| {
+        for group_index in direct_groups {
+            fmtln!(fmt, "{},", transform_groups.get(group_index).rust_name());
+        }
+    });
+    fmtln!(fmt, "];");
+}
+
+/// Generate the legalizer files.
+pub fn generate(
+    isas: &Vec<TargetIsa>,
+    format_registry: &FormatRegistry,
+    transform_groups: &TransformGroups,
+    filename_prefix: &str,
+    out_dir: &str,
+) -> Result<(), error::Error> {
+    let mut shared_group_names = HashSet::new();
+
+    for isa in isas {
+        let mut fmt = Formatter::new();
+        gen_isa(
+            isa,
+            format_registry,
+            transform_groups,
+            &mut shared_group_names,
+            &mut fmt,
+        );
+        fmt.update_file(format!("{}-{}.rs", filename_prefix, isa.name), out_dir)?;
+    }
+
+    // Generate shared legalize groups.
+    let mut fmt = Formatter::new();
+    let mut type_sets = UniqueTable::new();
+    let mut sorted_shared_group_names = Vec::from_iter(shared_group_names);
+    sorted_shared_group_names.sort();
+    for group_name in &sorted_shared_group_names {
+        let group = transform_groups.by_name(group_name);
+        gen_transform_group(
+            group,
+            format_registry,
+            transform_groups,
+            &mut type_sets,
+            &mut fmt,
+        );
+    }
+    gen_typesets_table(&type_sets, &mut fmt);
+    fmt.update_file(format!("{}r.rs", filename_prefix), out_dir)?;
+
+    Ok(())
+}
diff --git a/cranelift/codegen/meta/src/lib.rs b/cranelift/codegen/meta/src/lib.rs
index fccba327e0..bbf2a031a3 100644
--- a/cranelift/codegen/meta/src/lib.rs
+++ b/cranelift/codegen/meta/src/lib.rs
@@ -6,6 +6,7 @@ pub mod error;
 pub mod isa;
 
 mod gen_inst;
+mod gen_legalizer;
 mod gen_registers;
 mod gen_settings;
 mod gen_types;
@@ -45,6 +46,14 @@ pub fn generate(isas: &Vec<isa::Isa>, out_dir: &str) -> Result<(), error::Error>
         &out_dir,
     )?;
 
+    gen_legalizer::generate(
+        &isas,
+        &shared_defs.format_registry,
+        &shared_defs.transform_groups,
+        "new_legalize",
+        &out_dir,
+    )?;
+
     for isa in isas {
         gen_registers::generate(&isa, &format!("registers-{}.rs", isa.name), &out_dir)?;
         gen_settings::generate(
diff --git a/cranelift/codegen/meta/src/srcgen.rs b/cranelift/codegen/meta/src/srcgen.rs
index ac2b8e8e03..0a1d21c7b9 100644
--- a/cranelift/codegen/meta/src/srcgen.rs
+++ b/cranelift/codegen/meta/src/srcgen.rs
@@ -79,7 +79,7 @@ impl Formatter {
 
     /// Get a string containing whitespace outdented one level. Used for
     /// lines of code that are inside a single indented block.
-    fn _get_outdent(&mut self) -> String {
+    fn get_outdent(&mut self) -> String {
         self.indent_pop();
         let s = self.get_indent();
         self.indent_push();
@@ -98,8 +98,8 @@ impl Formatter {
     }
 
     /// Emit a line outdented one level.
-    pub fn _outdented_line(&mut self, s: &str) {
-        let new_line = format!("{}{}\n", self._get_outdent(), s);
+    pub fn outdented_line(&mut self, s: &str) {
+        let new_line = format!("{}{}\n", self.get_outdent(), s);
         self.lines.push(new_line);
     }
 
diff --git a/cranelift/codegen/meta/src/unique_table.rs b/cranelift/codegen/meta/src/unique_table.rs
index d7a26f67cc..e50a64f437 100644
--- a/cranelift/codegen/meta/src/unique_table.rs
+++ b/cranelift/codegen/meta/src/unique_table.rs
@@ -31,6 +31,9 @@ impl<'entries, T: Eq + Hash> UniqueTable<'entries, T> {
     pub fn len(&self) -> usize {
         self.table.len()
     }
+    pub fn get(&self, index: usize) -> &T {
+        self.table[index]
+    }
     pub fn iter(&self) -> slice::Iter<&'entries T> {
         self.table.iter()
     }