diff --git a/cranelift/codegen/meta/src/isa/x86/legalize.rs b/cranelift/codegen/meta/src/isa/x86/legalize.rs
new file mode 100644
index 0000000000..7a0cd8379c
--- /dev/null
+++ b/cranelift/codegen/meta/src/isa/x86/legalize.rs
@@ -0,0 +1,293 @@
+use crate::cdsl::ast::{bind, var, ExprBuilder, Literal};
+use crate::cdsl::inst::InstructionGroup;
+use crate::cdsl::xform::TransformGroupBuilder;
+
+use crate::shared::types::Int::{I32, I64};
+use crate::shared::Definitions as SharedDefinitions;
+
+pub fn define(shared: &mut SharedDefinitions, x86_instructions: &InstructionGroup) {
+    let mut group = TransformGroupBuilder::new(
+        "x86_expand",
+        r#"
+    Legalize instructions by expansion.
+
+    Use x86-specific instructions if needed."#,
+    )
+    .isa("x86")
+    .chain_with(shared.transform_groups.by_name("expand_flags").id);
+
+    // List of instructions.
+    let insts = &shared.instructions;
+    let band = insts.by_name("band");
+    let bor = insts.by_name("bor");
+    let clz = insts.by_name("clz");
+    let ctz = insts.by_name("ctz");
+    let fcmp = insts.by_name("fcmp");
+    let fcvt_from_uint = insts.by_name("fcvt_from_uint");
+    let fcvt_to_sint = insts.by_name("fcvt_to_sint");
+    let fcvt_to_uint = insts.by_name("fcvt_to_uint");
+    let fcvt_to_sint_sat = insts.by_name("fcvt_to_sint_sat");
+    let fcvt_to_uint_sat = insts.by_name("fcvt_to_uint_sat");
+    let fmax = insts.by_name("fmax");
+    let fmin = insts.by_name("fmin");
+    let iadd = insts.by_name("iadd");
+    let iconst = insts.by_name("iconst");
+    let imul = insts.by_name("imul");
+    let isub = insts.by_name("isub");
+    let popcnt = insts.by_name("popcnt");
+    let sdiv = insts.by_name("sdiv");
+    let selectif = insts.by_name("selectif");
+    let smulhi = insts.by_name("smulhi");
+    let srem = insts.by_name("srem");
+    let udiv = insts.by_name("udiv");
+    let umulhi = insts.by_name("umulhi");
+    let ushr_imm = insts.by_name("ushr_imm");
+    let urem = insts.by_name("urem");
+
+    let x86_bsf = x86_instructions.by_name("x86_bsf");
+    let x86_bsr = x86_instructions.by_name("x86_bsr");
+    let x86_umulx = x86_instructions.by_name("x86_umulx");
+    let x86_smulx = x86_instructions.by_name("x86_smulx");
+
+    // List of immediates.
+    let floatcc = shared.operand_kinds.by_name("floatcc");
+    let imm64 = shared.operand_kinds.by_name("imm64");
+    let intcc = shared.operand_kinds.by_name("intcc");
+
+    // Division and remainder.
+    //
+    // The srem expansion requires custom code because srem INT_MIN, -1 is not
+    // allowed to trap. The other ops need to check avoid_div_traps.
+    group.custom_legalize(sdiv, "expand_sdivrem");
+    group.custom_legalize(srem, "expand_sdivrem");
+    group.custom_legalize(udiv, "expand_udivrem");
+    group.custom_legalize(urem, "expand_udivrem");
+
+    // Double length (widening) multiplication.
+    let a = var("a");
+    let x = var("x");
+    let y = var("y");
+    let a1 = var("a1");
+    let a2 = var("a2");
+    let res_lo = var("res_lo");
+    let res_hi = var("res_hi");
+
+    group.legalize(
+        def!(res_hi = umulhi(x, y)),
+        vec![def!((res_lo, res_hi) = x86_umulx(x, y))],
+    );
+
+    group.legalize(
+        def!(res_hi = smulhi(x, y)),
+        vec![def!((res_lo, res_hi) = x86_smulx(x, y))],
+    );
+
+    // Floating point condition codes.
+    //
+    // The 8 condition codes in `supported_floatccs` are directly supported by a
+    // `ucomiss` or `ucomisd` instruction. The remaining codes need legalization
+    // patterns.
+
+    let floatcc_eq = Literal::enumerator_for(floatcc, "eq");
+    let floatcc_ord = Literal::enumerator_for(floatcc, "ord");
+    let floatcc_ueq = Literal::enumerator_for(floatcc, "ueq");
+    let floatcc_ne = Literal::enumerator_for(floatcc, "ne");
+    let floatcc_uno = Literal::enumerator_for(floatcc, "uno");
+    let floatcc_one = Literal::enumerator_for(floatcc, "one");
+
+    // Equality needs an explicit `ord` test which checks the parity bit.
+    group.legalize(
+        def!(a = fcmp(floatcc_eq, x, y)),
+        vec![
+            def!(a1 = fcmp(floatcc_ord, x, y)),
+            def!(a2 = fcmp(floatcc_ueq, x, y)),
+            def!(a = band(a1, a2)),
+        ],
+    );
+    group.legalize(
+        def!(a = fcmp(floatcc_ne, x, y)),
+        vec![
+            def!(a1 = fcmp(floatcc_uno, x, y)),
+            def!(a2 = fcmp(floatcc_one, x, y)),
+            def!(a = bor(a1, a2)),
+        ],
+    );
+
+    let floatcc_lt = &Literal::enumerator_for(floatcc, "lt");
+    let floatcc_gt = &Literal::enumerator_for(floatcc, "gt");
+    let floatcc_le = &Literal::enumerator_for(floatcc, "le");
+    let floatcc_ge = &Literal::enumerator_for(floatcc, "ge");
+    let floatcc_ugt = &Literal::enumerator_for(floatcc, "ugt");
+    let floatcc_ult = &Literal::enumerator_for(floatcc, "ult");
+    let floatcc_uge = &Literal::enumerator_for(floatcc, "uge");
+    let floatcc_ule = &Literal::enumerator_for(floatcc, "ule");
+
+    // Inequalities that need to be reversed.
+    for &(cc, rev_cc) in &[
+        (floatcc_lt, floatcc_gt),
+        (floatcc_le, floatcc_ge),
+        (floatcc_ugt, floatcc_ult),
+        (floatcc_uge, floatcc_ule),
+    ] {
+        group.legalize(def!(a = fcmp(cc, x, y)), vec![def!(a = fcmp(rev_cc, y, x))]);
+    }
+
+    // We need to modify the CFG for min/max legalization.
+    group.custom_legalize(fmin, "expand_minmax");
+    group.custom_legalize(fmax, "expand_minmax");
+
+    // Conversions from unsigned need special handling.
+    group.custom_legalize(fcvt_from_uint, "expand_fcvt_from_uint");
+    // Conversions from float to int can trap and modify the control flow graph.
+    group.custom_legalize(fcvt_to_sint, "expand_fcvt_to_sint");
+    group.custom_legalize(fcvt_to_uint, "expand_fcvt_to_uint");
+    group.custom_legalize(fcvt_to_sint_sat, "expand_fcvt_to_sint_sat");
+    group.custom_legalize(fcvt_to_uint_sat, "expand_fcvt_to_uint_sat");
+
+    // Count leading and trailing zeroes, for baseline x86_64
+    let c_minus_one = var("c_minus_one");
+    let c_thirty_one = var("c_thirty_one");
+    let c_thirty_two = var("c_thirty_two");
+    let c_sixty_three = var("c_sixty_three");
+    let c_sixty_four = var("c_sixty_four");
+    let index1 = var("index1");
+    let r2flags = var("r2flags");
+    let index2 = var("index2");
+
+    let intcc_eq = Literal::enumerator_for(intcc, "eq");
+    let imm64_minus_one = Literal::constant(imm64, -1);
+    let imm64_63 = Literal::constant(imm64, 63);
+    group.legalize(
+        def!(a = clz.I64(x)),
+        vec![
+            def!(c_minus_one = iconst(imm64_minus_one)),
+            def!(c_sixty_three = iconst(imm64_63)),
+            def!((index1, r2flags) = x86_bsr(x)),
+            def!(index2 = selectif(intcc_eq, r2flags, c_minus_one, index1)),
+            def!(a = isub(c_sixty_three, index2)),
+        ],
+    );
+
+    let imm64_31 = Literal::constant(imm64, 31);
+    group.legalize(
+        def!(a = clz.I32(x)),
+        vec![
+            def!(c_minus_one = iconst(imm64_minus_one)),
+            def!(c_thirty_one = iconst(imm64_31)),
+            def!((index1, r2flags) = x86_bsr(x)),
+            def!(index2 = selectif(intcc_eq, r2flags, c_minus_one, index1)),
+            def!(a = isub(c_thirty_one, index2)),
+        ],
+    );
+
+    let imm64_64 = Literal::constant(imm64, 64);
+    group.legalize(
+        def!(a = ctz.I64(x)),
+        vec![
+            def!(c_sixty_four = iconst(imm64_64)),
+            def!((index1, r2flags) = x86_bsf(x)),
+            def!(a = selectif(intcc_eq, r2flags, c_sixty_four, index1)),
+        ],
+    );
+
+    let imm64_32 = Literal::constant(imm64, 32);
+    group.legalize(
+        def!(a = ctz.I32(x)),
+        vec![
+            def!(c_thirty_two = iconst(imm64_32)),
+            def!((index1, r2flags) = x86_bsf(x)),
+            def!(a = selectif(intcc_eq, r2flags, c_thirty_two, index1)),
+        ],
+    );
+
+    // Population count for baseline x86_64
+    let qv1 = var("qv1");
+    let qv3 = var("qv3");
+    let qv4 = var("qv4");
+    let qv5 = var("qv5");
+    let qv6 = var("qv6");
+    let qv7 = var("qv7");
+    let qv8 = var("qv8");
+    let qv9 = var("qv9");
+    let qv10 = var("qv10");
+    let qv11 = var("qv11");
+    let qv12 = var("qv12");
+    let qv13 = var("qv13");
+    let qv14 = var("qv14");
+    let qv15 = var("qv15");
+    let qv16 = var("qv16");
+    let qc77 = var("qc77");
+    #[allow(non_snake_case)]
+    let qc0F = var("qc0F");
+    let qc01 = var("qc01");
+
+    let imm64_1 = Literal::constant(imm64, 1);
+    let imm64_4 = Literal::constant(imm64, 4);
+    group.legalize(
+        def!(qv16 = popcnt.I64(qv1)),
+        vec![
+            def!(qv3 = ushr_imm(qv1, imm64_1)),
+            def!(qc77 = iconst(Literal::constant(imm64, 0x7777777777777777))),
+            def!(qv4 = band(qv3, qc77)),
+            def!(qv5 = isub(qv1, qv4)),
+            def!(qv6 = ushr_imm(qv4, imm64_1)),
+            def!(qv7 = band(qv6, qc77)),
+            def!(qv8 = isub(qv5, qv7)),
+            def!(qv9 = ushr_imm(qv7, imm64_1)),
+            def!(qv10 = band(qv9, qc77)),
+            def!(qv11 = isub(qv8, qv10)),
+            def!(qv12 = ushr_imm(qv11, imm64_4)),
+            def!(qv13 = iadd(qv11, qv12)),
+            def!(qc0F = iconst(Literal::constant(imm64, 0x0F0F0F0F0F0F0F0F))),
+            def!(qv14 = band(qv13, qc0F)),
+            def!(qc01 = iconst(Literal::constant(imm64, 0x0101010101010101))),
+            def!(qv15 = imul(qv14, qc01)),
+            def!(qv16 = ushr_imm(qv15, Literal::constant(imm64, 56))),
+        ],
+    );
+
+    let lv1 = var("lv1");
+    let lv3 = var("lv3");
+    let lv4 = var("lv4");
+    let lv5 = var("lv5");
+    let lv6 = var("lv6");
+    let lv7 = var("lv7");
+    let lv8 = var("lv8");
+    let lv9 = var("lv9");
+    let lv10 = var("lv10");
+    let lv11 = var("lv11");
+    let lv12 = var("lv12");
+    let lv13 = var("lv13");
+    let lv14 = var("lv14");
+    let lv15 = var("lv15");
+    let lv16 = var("lv16");
+    let lc77 = var("lc77");
+    #[allow(non_snake_case)]
+    let lc0F = var("lc0F");
+    let lc01 = var("lc01");
+
+    group.legalize(
+        def!(lv16 = popcnt.I32(lv1)),
+        vec![
+            def!(lv3 = ushr_imm(lv1, imm64_1)),
+            def!(lc77 = iconst(Literal::constant(imm64, 0x77777777))),
+            def!(lv4 = band(lv3, lc77)),
+            def!(lv5 = isub(lv1, lv4)),
+            def!(lv6 = ushr_imm(lv4, imm64_1)),
+            def!(lv7 = band(lv6, lc77)),
+            def!(lv8 = isub(lv5, lv7)),
+            def!(lv9 = ushr_imm(lv7, imm64_1)),
+            def!(lv10 = band(lv9, lc77)),
+            def!(lv11 = isub(lv8, lv10)),
+            def!(lv12 = ushr_imm(lv11, imm64_4)),
+            def!(lv13 = iadd(lv11, lv12)),
+            def!(lc0F = iconst(Literal::constant(imm64, 0x0F0F0F0F))),
+            def!(lv14 = band(lv13, lc0F)),
+            def!(lc01 = iconst(Literal::constant(imm64, 0x01010101))),
+            def!(lv15 = imul(lv14, lc01)),
+            def!(lv16 = ushr_imm(lv15, Literal::constant(imm64, 24))),
+        ],
+    );
+
+    group.finish_and_add_to(&mut shared.transform_groups);
+}
diff --git a/cranelift/codegen/meta/src/shared/legalize.rs b/cranelift/codegen/meta/src/shared/legalize.rs
new file mode 100644
index 0000000000..172d6fd981
--- /dev/null
+++ b/cranelift/codegen/meta/src/shared/legalize.rs
@@ -0,0 +1,785 @@
+use crate::cdsl::ast::{bind, var, ExprBuilder, Literal};
+use crate::cdsl::inst::{Instruction, InstructionGroup};
+use crate::cdsl::xform::{TransformGroupBuilder, TransformGroups};
+
+use crate::shared::OperandKinds;
+
+use crate::shared::types::Float::{F32, F64};
+use crate::shared::types::Int::{I16, I32, I64, I8};
+
+pub fn define(insts: &InstructionGroup, immediates: &OperandKinds) -> TransformGroups {
+    let mut narrow = TransformGroupBuilder::new(
+        "narrow",
+        r#"
+        Legalize instructions by narrowing.
+
+        The transformations in the 'narrow' group work by expressing
+        instructions in terms of smaller types. Operations on vector types are
+        expressed in terms of vector types with fewer lanes, and integer
+        operations are expressed in terms of smaller integer types.
+    "#,
+    );
+
+    let mut widen = TransformGroupBuilder::new(
+        "widen",
+        r#"
+        Legalize instructions by widening.
+
+        The transformations in the 'widen' group work by expressing
+        instructions in terms of larger types.
+    "#,
+    );
+
+    let mut expand = TransformGroupBuilder::new(
+        "expand",
+        r#"
+        Legalize instructions by expansion.
+
+        Rewrite instructions in terms of other instructions, generally
+        operating on the same types as the original instructions.
+    "#,
+    );
+
+    // List of instructions.
+    let band = insts.by_name("band");
+    let band_imm = insts.by_name("band_imm");
+    let band_not = insts.by_name("band_not");
+    let bint = insts.by_name("bint");
+    let bitrev = insts.by_name("bitrev");
+    let bnot = insts.by_name("bnot");
+    let bor = insts.by_name("bor");
+    let bor_imm = insts.by_name("bor_imm");
+    let bor_not = insts.by_name("bor_not");
+    let br_icmp = insts.by_name("br_icmp");
+    let br_table = insts.by_name("br_table");
+    let bxor = insts.by_name("bxor");
+    let bxor_imm = insts.by_name("bxor_imm");
+    let bxor_not = insts.by_name("bxor_not");
+    let cls = insts.by_name("cls");
+    let clz = insts.by_name("clz");
+    let ctz = insts.by_name("ctz");
+    let fabs = insts.by_name("fabs");
+    let f32const = insts.by_name("f32const");
+    let f64const = insts.by_name("f64const");
+    let fcopysign = insts.by_name("fcopysign");
+    let fneg = insts.by_name("fneg");
+    let iadd = insts.by_name("iadd");
+    let iadd_carry = insts.by_name("iadd_carry");
+    let iadd_cin = insts.by_name("iadd_cin");
+    let iadd_cout = insts.by_name("iadd_cout");
+    let iadd_imm = insts.by_name("iadd_imm");
+    let icmp = insts.by_name("icmp");
+    let icmp_imm = insts.by_name("icmp_imm");
+    let iconcat = insts.by_name("iconcat");
+    let iconst = insts.by_name("iconst");
+    let ifcmp = insts.by_name("ifcmp");
+    let ifcmp_imm = insts.by_name("ifcmp_imm");
+    let imul = insts.by_name("imul");
+    let imul_imm = insts.by_name("imul_imm");
+    let ireduce = insts.by_name("ireduce");
+    let irsub_imm = insts.by_name("irsub_imm");
+    let ishl = insts.by_name("ishl");
+    let ishl_imm = insts.by_name("ishl_imm");
+    let isplit = insts.by_name("isplit");
+    let istore8 = insts.by_name("istore8");
+    let istore16 = insts.by_name("istore16");
+    let isub = insts.by_name("isub");
+    let isub_bin = insts.by_name("isub_bin");
+    let isub_borrow = insts.by_name("isub_borrow");
+    let isub_bout = insts.by_name("isub_bout");
+    let load = insts.by_name("load");
+    let popcnt = insts.by_name("popcnt");
+    let rotl = insts.by_name("rotl");
+    let rotl_imm = insts.by_name("rotl_imm");
+    let rotr = insts.by_name("rotr");
+    let rotr_imm = insts.by_name("rotr_imm");
+    let sdiv = insts.by_name("sdiv");
+    let sdiv_imm = insts.by_name("sdiv_imm");
+    let select = insts.by_name("select");
+    let sextend = insts.by_name("sextend");
+    let sshr = insts.by_name("sshr");
+    let sshr_imm = insts.by_name("sshr_imm");
+    let srem = insts.by_name("srem");
+    let srem_imm = insts.by_name("srem_imm");
+    let store = insts.by_name("store");
+    let udiv = insts.by_name("udiv");
+    let udiv_imm = insts.by_name("udiv_imm");
+    let uextend = insts.by_name("uextend");
+    let uload8 = insts.by_name("uload8");
+    let uload16 = insts.by_name("uload16");
+    let ushr = insts.by_name("ushr");
+    let ushr_imm = insts.by_name("ushr_imm");
+    let urem = insts.by_name("urem");
+    let urem_imm = insts.by_name("urem_imm");
+    let trapif = insts.by_name("trapif");
+    let trapnz = insts.by_name("trapnz");
+    let trapz = insts.by_name("trapz");
+
+    // Custom expansions for memory objects.
+    expand.custom_legalize(insts.by_name("global_value"), "expand_global_value");
+    expand.custom_legalize(insts.by_name("heap_addr"), "expand_heap_addr");
+    expand.custom_legalize(insts.by_name("table_addr"), "expand_table_addr");
+
+    // Custom expansions for calls.
+    expand.custom_legalize(insts.by_name("call"), "expand_call");
+
+    // Custom expansions that need to change the CFG.
+    // TODO: Add sufficient XForm syntax that we don't need to hand-code these.
+    expand.custom_legalize(trapz, "expand_cond_trap");
+    expand.custom_legalize(trapnz, "expand_cond_trap");
+    expand.custom_legalize(br_table, "expand_br_table");
+    expand.custom_legalize(select, "expand_select");
+
+    // Custom expansions for floating point constants.
+    // These expansions require bit-casting or creating constant pool entries.
+    expand.custom_legalize(f32const, "expand_fconst");
+    expand.custom_legalize(f64const, "expand_fconst");
+
+    // Custom expansions for stack memory accesses.
+    expand.custom_legalize(insts.by_name("stack_load"), "expand_stack_load");
+    expand.custom_legalize(insts.by_name("stack_store"), "expand_stack_store");
+
+    // List of immediates.
+    let imm64 = immediates.by_name("imm64");
+    let ieee32 = immediates.by_name("ieee32");
+    let ieee64 = immediates.by_name("ieee64");
+    let intcc = immediates.by_name("intcc");
+
+    // List of variables to reuse in patterns.
+    let x = var("x");
+    let y = var("y");
+    let z = var("z");
+    let a = var("a");
+    let a1 = var("a1");
+    let a2 = var("a2");
+    let a3 = var("a3");
+    let a4 = var("a4");
+    let b = var("b");
+    let b1 = var("b1");
+    let b2 = var("b2");
+    let b3 = var("b3");
+    let b4 = var("b4");
+    let b_in = var("b_in");
+    let b_int = var("b_int");
+    let c = var("c");
+    let c1 = var("c1");
+    let c2 = var("c2");
+    let c3 = var("c3");
+    let c4 = var("c4");
+    let c_in = var("c_in");
+    let c_int = var("c_int");
+    let d = var("d");
+    let d1 = var("d1");
+    let d2 = var("d2");
+    let d3 = var("d3");
+    let d4 = var("d4");
+    let e = var("e");
+    let e1 = var("e1");
+    let e2 = var("e2");
+    let e3 = var("e3");
+    let e4 = var("e4");
+    let f = var("f");
+    let f1 = var("f1");
+    let f2 = var("f2");
+    let xl = var("xl");
+    let xh = var("xh");
+    let yl = var("yl");
+    let yh = var("yh");
+    let al = var("al");
+    let ah = var("ah");
+    let cc = var("cc");
+    let ptr = var("ptr");
+    let flags = var("flags");
+    let offset = var("off");
+
+    narrow.legalize(
+        def!(a = iadd(x, y)),
+        vec![
+            def!((xl, xh) = isplit(x)),
+            def!((yl, yh) = isplit(y)),
+            def!((al, c) = iadd_cout(xl, yl)),
+            def!(ah = iadd_cin(xh, yh, c)),
+            def!(a = iconcat(al, ah)),
+        ],
+    );
+
+    narrow.legalize(
+        def!(a = isub(x, y)),
+        vec![
+            def!((xl, xh) = isplit(x)),
+            def!((yl, yh) = isplit(y)),
+            def!((al, b) = isub_bout(xl, yl)),
+            def!(ah = isub_bin(xh, yh, b)),
+            def!(a = iconcat(al, ah)),
+        ],
+    );
+
+    for &bin_op in &[band, bor, bxor] {
+        narrow.legalize(
+            def!(a = bin_op(x, y)),
+            vec![
+                def!((xl, xh) = isplit(x)),
+                def!((yl, yh) = isplit(y)),
+                def!(al = bin_op(xl, yl)),
+                def!(ah = bin_op(xh, yh)),
+                def!(a = iconcat(al, ah)),
+            ],
+        );
+    }
+
+    narrow.legalize(
+        def!(a = select(c, x, y)),
+        vec![
+            def!((xl, xh) = isplit(x)),
+            def!((yl, yh) = isplit(y)),
+            def!(al = select(c, xl, yl)),
+            def!(ah = select(c, xh, yh)),
+            def!(a = iconcat(al, ah)),
+        ],
+    );
+
+    // Widen instructions with one input operand.
+    for &op in &[bnot, popcnt] {
+        for &int_ty in &[I8, I16] {
+            widen.legalize(
+                def!(a = op.int_ty(b)),
+                vec![
+                    def!(x = uextend.I32(b)),
+                    def!(z = op.I32(x)),
+                    def!(a = ireduce.int_ty(z)),
+                ],
+            );
+        }
+    }
+
+    // Widen instructions with two input operands.
+    let mut widen_two_arg = |signed: bool, op: &Instruction| {
+        for &int_ty in &[I8, I16] {
+            let sign_ext_op = if signed { sextend } else { uextend };
+            widen.legalize(
+                def!(a = op.int_ty(b, c)),
+                vec![
+                    def!(x = sign_ext_op.I32(b)),
+                    def!(y = sign_ext_op.I32(c)),
+                    def!(z = op.I32(x, y)),
+                    def!(a = ireduce.int_ty(z)),
+                ],
+            );
+        }
+    };
+
+    for bin_op in &[
+        iadd, isub, imul, udiv, urem, band, bor, bxor, band_not, bor_not, bxor_not,
+    ] {
+        widen_two_arg(false, bin_op);
+    }
+    for bin_op in &[sdiv, srem] {
+        widen_two_arg(true, bin_op);
+    }
+
+    // Widen instructions using immediate operands.
+    let mut widen_imm = |signed: bool, op: &Instruction| {
+        for &int_ty in &[I8, I16] {
+            let sign_ext_op = if signed { sextend } else { uextend };
+            widen.legalize(
+                def!(a = op.int_ty(b, c)),
+                vec![
+                    def!(x = sign_ext_op.I32(b)),
+                    def!(z = op.I32(x, c)),
+                    def!(a = ireduce.int_ty(z)),
+                ],
+            );
+        }
+    };
+
+    for bin_op in &[
+        iadd_imm, imul_imm, udiv_imm, urem_imm, band_imm, bor_imm, bxor_imm, irsub_imm,
+    ] {
+        widen_imm(false, bin_op);
+    }
+    for bin_op in &[sdiv_imm, srem_imm] {
+        widen_imm(true, bin_op);
+    }
+
+    for &(int_ty, num) in &[(I8, 24), (I16, 16)] {
+        let imm = Literal::constant(imm64, -num);
+
+        widen.legalize(
+            def!(a = clz.int_ty(b)),
+            vec![
+                def!(c = uextend.I32(b)),
+                def!(d = clz.I32(c)),
+                def!(e = iadd_imm(d, imm)),
+                def!(a = ireduce.int_ty(e)),
+            ],
+        );
+
+        widen.legalize(
+            def!(a = cls.int_ty(b)),
+            vec![
+                def!(c = sextend.I32(b)),
+                def!(d = cls.I32(c)),
+                def!(e = iadd_imm(d, imm)),
+                def!(a = ireduce.int_ty(e)),
+            ],
+        );
+    }
+
+    for &(int_ty, num) in &[(I8, 1 << 8), (I16, 1 << 16)] {
+        let num = Literal::constant(imm64, num);
+        widen.legalize(
+            def!(a = ctz.int_ty(b)),
+            vec![
+                def!(c = uextend.I32(b)),
+                // When `b` is zero, returns the size of x in bits.
+                def!(d = bor_imm(c, num)),
+                def!(e = ctz.I32(d)),
+                def!(a = ireduce.int_ty(e)),
+            ],
+        );
+    }
+
+    // iconst
+    for &int_ty in &[I8, I16] {
+        widen.legalize(
+            def!(a = iconst.int_ty(b)),
+            vec![def!(c = iconst.I32(b)), def!(a = ireduce.int_ty(c))],
+        );
+    }
+
+    for &extend_op in &[uextend, sextend] {
+        // The sign extension operators have two typevars: the result has one and controls the
+        // instruction, then the input has one.
+        let bound = bind(bind(extend_op, I16), I8);
+        widen.legalize(
+            def!(a = bound(b)),
+            vec![def!(c = extend_op.I32(b)), def!(a = ireduce(c))],
+        );
+    }
+
+    widen.legalize(
+        def!(store.I8(flags, a, ptr, offset)),
+        vec![
+            def!(b = uextend.I32(a)),
+            def!(istore8(flags, b, ptr, offset)),
+        ],
+    );
+
+    widen.legalize(
+        def!(store.I16(flags, a, ptr, offset)),
+        vec![
+            def!(b = uextend.I32(a)),
+            def!(istore16(flags, b, ptr, offset)),
+        ],
+    );
+
+    widen.legalize(
+        def!(a = load.I8(flags, ptr, offset)),
+        vec![
+            def!(b = uload8.I32(flags, ptr, offset)),
+            def!(a = ireduce(b)),
+        ],
+    );
+
+    widen.legalize(
+        def!(a = load.I16(flags, ptr, offset)),
+        vec![
+            def!(b = uload16.I32(flags, ptr, offset)),
+            def!(a = ireduce(b)),
+        ],
+    );
+
+    for &int_ty in &[I8, I16] {
+        widen.legalize(
+            def!(br_table.int_ty(x, y, z)),
+            vec![def!(b = uextend.I32(x)), def!(br_table(b, y, z))],
+        );
+    }
+
+    for &int_ty in &[I8, I16] {
+        widen.legalize(
+            def!(a = bint.int_ty(b)),
+            vec![def!(x = bint.I32(b)), def!(a = ireduce.int_ty(x))],
+        );
+    }
+
+    for &int_ty in &[I8, I16] {
+        for &op in &[ishl, ishl_imm, ushr, ushr_imm] {
+            widen.legalize(
+                def!(a = op.int_ty(b, c)),
+                vec![
+                    def!(x = uextend.I32(b)),
+                    def!(z = op.I32(x, c)),
+                    def!(a = ireduce.int_ty(z)),
+                ],
+            );
+        }
+
+        for &op in &[sshr, sshr_imm] {
+            widen.legalize(
+                def!(a = op.int_ty(b, c)),
+                vec![
+                    def!(x = sextend.I32(b)),
+                    def!(z = op.I32(x, c)),
+                    def!(a = ireduce.int_ty(z)),
+                ],
+            );
+        }
+
+        for cc in &["eq", "ne", "ugt", "ult", "uge", "ule"] {
+            let w_cc = Literal::enumerator_for(intcc, cc);
+            widen.legalize(
+                def!(a = icmp_imm.int_ty(w_cc, b, c)),
+                vec![def!(x = uextend.I32(b)), def!(a = icmp_imm(w_cc, x, c))],
+            );
+            widen.legalize(
+                def!(a = icmp.int_ty(w_cc, b, c)),
+                vec![
+                    def!(x = uextend.I32(b)),
+                    def!(y = uextend.I32(c)),
+                    def!(a = icmp.I32(w_cc, x, y)),
+                ],
+            );
+        }
+
+        for cc in &["sgt", "slt", "sge", "sle"] {
+            let w_cc = Literal::enumerator_for(intcc, cc);
+            widen.legalize(
+                def!(a = icmp_imm.int_ty(w_cc, b, c)),
+                vec![def!(x = sextend.I32(b)), def!(a = icmp_imm(w_cc, x, c))],
+            );
+
+            widen.legalize(
+                def!(a = icmp.int_ty(w_cc, b, c)),
+                vec![
+                    def!(x = sextend.I32(b)),
+                    def!(y = sextend.I32(c)),
+                    def!(a = icmp(w_cc, x, y)),
+                ],
+            );
+        }
+    }
+
+    // Expand integer operations with carry for RISC architectures that don't have
+    // the flags.
+    let intcc_ult = Literal::enumerator_for(intcc, "ult");
+    expand.legalize(
+        def!((a, c) = iadd_cout(x, y)),
+        vec![def!(a = iadd(x, y)), def!(c = icmp(intcc_ult, a, x))],
+    );
+
+    let intcc_ugt = Literal::enumerator_for(intcc, "ugt");
+    expand.legalize(
+        def!((a, b) = isub_bout(x, y)),
+        vec![def!(a = isub(x, y)), def!(b = icmp(intcc_ugt, a, x))],
+    );
+
+    expand.legalize(
+        def!(a = iadd_cin(x, y, c)),
+        vec![
+            def!(a1 = iadd(x, y)),
+            def!(c_int = bint(c)),
+            def!(a = iadd(a1, c_int)),
+        ],
+    );
+
+    expand.legalize(
+        def!(a = isub_bin(x, y, b)),
+        vec![
+            def!(a1 = isub(x, y)),
+            def!(b_int = bint(b)),
+            def!(a = isub(a1, b_int)),
+        ],
+    );
+
+    expand.legalize(
+        def!((a, c) = iadd_carry(x, y, c_in)),
+        vec![
+            def!((a1, c1) = iadd_cout(x, y)),
+            def!(c_int = bint(c_in)),
+            def!((a, c2) = iadd_cout(a1, c_int)),
+            def!(c = bor(c1, c2)),
+        ],
+    );
+
+    expand.legalize(
+        def!((a, b) = isub_borrow(x, y, b_in)),
+        vec![
+            def!((a1, b1) = isub_bout(x, y)),
+            def!(b_int = bint(b_in)),
+            def!((a, b2) = isub_bout(a1, b_int)),
+            def!(b = bor(b1, b2)),
+        ],
+    );
+
+    // Expansions for immediate operands that are out of range.
+    for &(inst_imm, inst) in &[
+        (iadd_imm, iadd),
+        (imul_imm, imul),
+        (sdiv_imm, sdiv),
+        (udiv_imm, udiv),
+        (srem_imm, srem),
+        (urem_imm, urem),
+        (band_imm, band),
+        (bor_imm, bor),
+        (bxor_imm, bxor),
+        (ifcmp_imm, ifcmp),
+    ] {
+        expand.legalize(
+            def!(a = inst_imm(x, y)),
+            vec![def!(a1 = iconst(y)), def!(a = inst(x, a1))],
+        );
+    }
+
+    expand.legalize(
+        def!(a = irsub_imm(y, x)),
+        vec![def!(a1 = iconst(x)), def!(a = isub(a1, y))],
+    );
+
+    // Rotates and shifts.
+    for &(inst_imm, inst) in &[
+        (rotl_imm, rotl),
+        (rotr_imm, rotr),
+        (ishl_imm, ishl),
+        (sshr_imm, sshr),
+        (ushr_imm, ushr),
+    ] {
+        expand.legalize(
+            def!(a = inst_imm(x, y)),
+            vec![def!(a1 = iconst.I32(y)), def!(a = inst(x, a1))],
+        );
+    }
+
+    expand.legalize(
+        def!(a = icmp_imm(cc, x, y)),
+        vec![def!(a1 = iconst(y)), def!(a = icmp(cc, x, a1))],
+    );
+
+    //# Expansions for *_not variants of bitwise ops.
+    for &(inst_not, inst) in &[(band_not, band), (bor_not, bor), (bxor_not, bxor)] {
+        expand.legalize(
+            def!(a = inst_not(x, y)),
+            vec![def!(a1 = bnot(y)), def!(a = inst(x, a1))],
+        );
+    }
+
+    //# Expand bnot using xor.
+    let minus_one = Literal::constant(imm64, -1);
+    expand.legalize(
+        def!(a = bnot(x)),
+        vec![def!(y = iconst(minus_one)), def!(a = bxor(x, y))],
+    );
+
+    //# Expand bitrev
+    //# Adapted from Stack Overflow.
+    //# https://stackoverflow.com/questions/746171/most-efficient-algorithm-for-bit-reversal-from-msb-lsb-to-lsb-msb-in-c
+    let imm64_1 = Literal::constant(imm64, 1);
+    let imm64_2 = Literal::constant(imm64, 2);
+    let imm64_4 = Literal::constant(imm64, 4);
+
+    widen.legalize(
+        def!(a = bitrev.I8(x)),
+        vec![
+            def!(a1 = band_imm(x, Literal::constant(imm64, 0xaa))),
+            def!(a2 = ushr_imm(a1, imm64_1)),
+            def!(a3 = band_imm(x, Literal::constant(imm64, 0x55))),
+            def!(a4 = ishl_imm(a3, imm64_1)),
+            def!(b = bor(a2, a4)),
+            def!(b1 = band_imm(b, Literal::constant(imm64, 0xcc))),
+            def!(b2 = ushr_imm(b1, imm64_2)),
+            def!(b3 = band_imm(b, Literal::constant(imm64, 0x33))),
+            def!(b4 = ishl_imm(b3, imm64_2)),
+            def!(c = bor(b2, b4)),
+            def!(c1 = band_imm(c, Literal::constant(imm64, 0xf0))),
+            def!(c2 = ushr_imm(c1, imm64_4)),
+            def!(c3 = band_imm(c, Literal::constant(imm64, 0x0f))),
+            def!(c4 = ishl_imm(c3, imm64_4)),
+            def!(a = bor(c2, c4)),
+        ],
+    );
+
+    let imm64_8 = Literal::constant(imm64, 8);
+
+    widen.legalize(
+        def!(a = bitrev.I16(x)),
+        vec![
+            def!(a1 = band_imm(x, Literal::constant(imm64, 0xaaaa))),
+            def!(a2 = ushr_imm(a1, imm64_1)),
+            def!(a3 = band_imm(x, Literal::constant(imm64, 0x5555))),
+            def!(a4 = ishl_imm(a3, imm64_1)),
+            def!(b = bor(a2, a4)),
+            def!(b1 = band_imm(b, Literal::constant(imm64, 0xcccc))),
+            def!(b2 = ushr_imm(b1, imm64_2)),
+            def!(b3 = band_imm(b, Literal::constant(imm64, 0x3333))),
+            def!(b4 = ishl_imm(b3, imm64_2)),
+            def!(c = bor(b2, b4)),
+            def!(c1 = band_imm(c, Literal::constant(imm64, 0xf0f0))),
+            def!(c2 = ushr_imm(c1, imm64_4)),
+            def!(c3 = band_imm(c, Literal::constant(imm64, 0x0f0f))),
+            def!(c4 = ishl_imm(c3, imm64_4)),
+            def!(d = bor(c2, c4)),
+            def!(d1 = band_imm(d, Literal::constant(imm64, 0xff00))),
+            def!(d2 = ushr_imm(d1, imm64_8)),
+            def!(d3 = band_imm(d, Literal::constant(imm64, 0x00ff))),
+            def!(d4 = ishl_imm(d3, imm64_8)),
+            def!(a = bor(d2, d4)),
+        ],
+    );
+
+    let imm64_16 = Literal::constant(imm64, 16);
+
+    expand.legalize(
+        def!(a = bitrev.I32(x)),
+        vec![
+            def!(a1 = band_imm(x, Literal::constant(imm64, 0xaaaaaaaa))),
+            def!(a2 = ushr_imm(a1, imm64_1)),
+            def!(a3 = band_imm(x, Literal::constant(imm64, 0x55555555))),
+            def!(a4 = ishl_imm(a3, imm64_1)),
+            def!(b = bor(a2, a4)),
+            def!(b1 = band_imm(b, Literal::constant(imm64, 0xcccccccc))),
+            def!(b2 = ushr_imm(b1, imm64_2)),
+            def!(b3 = band_imm(b, Literal::constant(imm64, 0x33333333))),
+            def!(b4 = ishl_imm(b3, imm64_2)),
+            def!(c = bor(b2, b4)),
+            def!(c1 = band_imm(c, Literal::constant(imm64, 0xf0f0f0f0))),
+            def!(c2 = ushr_imm(c1, imm64_4)),
+            def!(c3 = band_imm(c, Literal::constant(imm64, 0x0f0f0f0f))),
+            def!(c4 = ishl_imm(c3, imm64_4)),
+            def!(d = bor(c2, c4)),
+            def!(d1 = band_imm(d, Literal::constant(imm64, 0xff00ff00))),
+            def!(d2 = ushr_imm(d1, imm64_8)),
+            def!(d3 = band_imm(d, Literal::constant(imm64, 0x00ff00ff))),
+            def!(d4 = ishl_imm(d3, imm64_8)),
+            def!(e = bor(d2, d4)),
+            def!(e1 = ushr_imm(e, imm64_16)),
+            def!(e2 = ishl_imm(e, imm64_16)),
+            def!(a = bor(e1, e2)),
+        ],
+    );
+
+    #[allow(overflowing_literals)]
+    let imm64_0xaaaaaaaaaaaaaaaa = Literal::constant(imm64, 0xaaaaaaaaaaaaaaaa);
+    let imm64_0x5555555555555555 = Literal::constant(imm64, 0x5555555555555555);
+    #[allow(overflowing_literals)]
+    let imm64_0xcccccccccccccccc = Literal::constant(imm64, 0xcccccccccccccccc);
+    let imm64_0x3333333333333333 = Literal::constant(imm64, 0x3333333333333333);
+    #[allow(overflowing_literals)]
+    let imm64_0xf0f0f0f0f0f0f0f0 = Literal::constant(imm64, 0xf0f0f0f0f0f0f0f0);
+    let imm64_0x0f0f0f0f0f0f0f0f = Literal::constant(imm64, 0x0f0f0f0f0f0f0f0f);
+    #[allow(overflowing_literals)]
+    let imm64_0xff00ff00ff00ff00 = Literal::constant(imm64, 0xff00ff00ff00ff00);
+    let imm64_0x00ff00ff00ff00ff = Literal::constant(imm64, 0x00ff00ff00ff00ff);
+    #[allow(overflowing_literals)]
+    let imm64_0xffff0000ffff0000 = Literal::constant(imm64, 0xffff0000ffff0000);
+    let imm64_0x0000ffff0000ffff = Literal::constant(imm64, 0x0000ffff0000ffff);
+    let imm64_32 = Literal::constant(imm64, 32);
+
+    expand.legalize(
+        def!(a = bitrev.I64(x)),
+        vec![
+            def!(a1 = band_imm(x, imm64_0xaaaaaaaaaaaaaaaa)),
+            def!(a2 = ushr_imm(a1, imm64_1)),
+            def!(a3 = band_imm(x, imm64_0x5555555555555555)),
+            def!(a4 = ishl_imm(a3, imm64_1)),
+            def!(b = bor(a2, a4)),
+            def!(b1 = band_imm(b, imm64_0xcccccccccccccccc)),
+            def!(b2 = ushr_imm(b1, imm64_2)),
+            def!(b3 = band_imm(b, imm64_0x3333333333333333)),
+            def!(b4 = ishl_imm(b3, imm64_2)),
+            def!(c = bor(b2, b4)),
+            def!(c1 = band_imm(c, imm64_0xf0f0f0f0f0f0f0f0)),
+            def!(c2 = ushr_imm(c1, imm64_4)),
+            def!(c3 = band_imm(c, imm64_0x0f0f0f0f0f0f0f0f)),
+            def!(c4 = ishl_imm(c3, imm64_4)),
+            def!(d = bor(c2, c4)),
+            def!(d1 = band_imm(d, imm64_0xff00ff00ff00ff00)),
+            def!(d2 = ushr_imm(d1, imm64_8)),
+            def!(d3 = band_imm(d, imm64_0x00ff00ff00ff00ff)),
+            def!(d4 = ishl_imm(d3, imm64_8)),
+            def!(e = bor(d2, d4)),
+            def!(e1 = band_imm(e, imm64_0xffff0000ffff0000)),
+            def!(e2 = ushr_imm(e1, imm64_16)),
+            def!(e3 = band_imm(e, imm64_0x0000ffff0000ffff)),
+            def!(e4 = ishl_imm(e3, imm64_16)),
+            def!(f = bor(e2, e4)),
+            def!(f1 = ushr_imm(f, imm64_32)),
+            def!(f2 = ishl_imm(f, imm64_32)),
+            def!(a = bor(f1, f2)),
+        ],
+    );
+
+    // Floating-point sign manipulations.
+    for &(ty, const_inst, minus_zero) in &[
+        (F32, f32const, &Literal::bits(ieee32, 0x80000000)),
+        (F64, f64const, &Literal::bits(ieee64, 0x8000000000000000)),
+    ] {
+        expand.legalize(
+            def!(a = fabs.ty(x)),
+            vec![def!(b = const_inst(minus_zero)), def!(a = band_not(x, b))],
+        );
+
+        expand.legalize(
+            def!(a = fneg.ty(x)),
+            vec![def!(b = const_inst(minus_zero)), def!(a = bxor(x, b))],
+        );
+
+        expand.legalize(
+            def!(a = fcopysign.ty(x, y)),
+            vec![
+                def!(b = const_inst(minus_zero)),
+                def!(a1 = band_not(x, b)),
+                def!(a2 = band(y, b)),
+                def!(a = bor(a1, a2)),
+            ],
+        );
+    }
+
+    expand.custom_legalize(br_icmp, "expand_br_icmp");
+
+    let mut groups = TransformGroups::new();
+
+    narrow.finish_and_add_to(&mut groups);
+    let expand_id = expand.finish_and_add_to(&mut groups);
+
+    // Expansions using CPU flags.
+    let mut expand_flags = TransformGroupBuilder::new(
+        "expand_flags",
+        r#"
+        Instruction expansions for architectures with flags.
+
+        Expand some instructions using CPU flags, then fall back to the normal
+        expansions. Not all architectures support CPU flags, so these patterns
+        are kept separate.
+    "#,
+    )
+    .chain_with(expand_id);
+
+    let imm64_0 = Literal::constant(imm64, 0);
+    let intcc_ne = Literal::enumerator_for(intcc, "ne");
+    let intcc_eq = Literal::enumerator_for(intcc, "eq");
+
+    expand_flags.legalize(
+        def!(trapnz(x, c)),
+        vec![
+            def!(a = ifcmp_imm(x, imm64_0)),
+            def!(trapif(intcc_ne, a, c)),
+        ],
+    );
+
+    expand_flags.legalize(
+        def!(trapz(x, c)),
+        vec![
+            def!(a = ifcmp_imm(x, imm64_0)),
+            def!(trapif(intcc_eq, a, c)),
+        ],
+    );
+
+    expand_flags.finish_and_add_to(&mut groups);
+
+    // XXX The order of declarations unfortunately matters to be compatible with the Python code.
+    // When it's all migrated, we can put this next to the narrow/expand finish_and_add_to calls
+    // above.
+    widen.finish_and_add_to(&mut groups);
+
+    groups
+}
diff --git a/cranelift/codegen/meta/src/shared/mod.rs b/cranelift/codegen/meta/src/shared/mod.rs
index 0e6a11f0e1..5237d9ba33 100644
--- a/cranelift/codegen/meta/src/shared/mod.rs
+++ b/cranelift/codegen/meta/src/shared/mod.rs
@@ -4,6 +4,7 @@ pub mod entities;
 pub mod formats;
 pub mod immediates;
 pub mod instructions;
+pub mod legalize;
 pub mod settings;
 pub mod types;
 
@@ -11,12 +12,14 @@ use crate::cdsl::formats::FormatRegistry;
 use crate::cdsl::inst::InstructionGroup;
 use crate::cdsl::operands::OperandKind;
 use crate::cdsl::settings::SettingGroup;
+use crate::cdsl::xform::TransformGroups;
 
 pub struct Definitions {
     pub settings: SettingGroup,
     pub instructions: InstructionGroup,
     pub operand_kinds: OperandKinds,
     pub format_registry: FormatRegistry,
+    pub transform_groups: TransformGroups,
 }
 
 pub struct OperandKinds(Vec<OperandKind>);
@@ -50,10 +53,14 @@ pub fn define() -> Definitions {
     let immediates = OperandKinds(immediates::define());
     let entities = OperandKinds(entities::define());
     let format_registry = formats::define(&immediates, &entities);
+    let instructions = instructions::define(&format_registry, &immediates, &entities);
+    let transform_groups = legalize::define(&instructions, &immediates);
+
     Definitions {
         settings: settings::define(),
-        instructions: instructions::define(&format_registry, &immediates, &entities),
+        instructions,
         operand_kinds: immediates,
         format_registry,
+        transform_groups,
     }
 }