diff --git a/cranelift/Cargo.toml b/cranelift/Cargo.toml
index 59e940b5d8..39e3ef182a 100644
--- a/cranelift/Cargo.toml
+++ b/cranelift/Cargo.toml
@@ -31,7 +31,7 @@ clap = "2.32.0"
 serde = "1.0.8"
 term = "0.5.1"
 capstone = { version = "0.5.0", optional = true }
-wabt = { version = "0.5", optional = true }
+wabt = { version = "0.6", optional = true }
 target-lexicon = "0.0.3"
 pretty_env_logger = "0.2.4"
 file-per-thread-logger = "0.1.1"
diff --git a/cranelift/filetests/isa/x86/legalize-byte-ops-i8.clif b/cranelift/filetests/isa/x86/legalize-byte-ops-i8.clif
new file mode 100644
index 0000000000..b0a318b8d4
--- /dev/null
+++ b/cranelift/filetests/isa/x86/legalize-byte-ops-i8.clif
@@ -0,0 +1,36 @@
+test compile
+target x86_64
+
+; regex: V=v\d+
+
+function u0:0(i8, i8) fast {
+fn0 = %black_box(i8)
+ss0 = explicit_slot 1 ; black box
+
+ebb0(v0: i8, v1: i8):
+    v99 = stack_addr.i64 ss0
+
+    ; check: istore8 $(V), $(V)
+
+    v2 = band v0, v1
+    store v2, v99
+    v3 = bor v0, v1
+    store v3, v99
+    v4 = bxor v0, v1
+    store v4, v99
+    v5 = bnot v0
+    store v5, v99
+    v6 = band_not v0, v1
+    store v6, v99
+    v7 = bor_not v0, v1
+    store v7, v99
+    v8 = bxor_not v0, v1
+    store v8, v99
+    v9 = band_imm v0, 42
+    store v9, v99
+    v10 = bor_imm v0, 42
+    store v10, v99
+    v11 = bxor_imm v0, 42
+    store v11, v99
+    return
+}
diff --git a/cranelift/filetests/isa/x86/legalize-icmp-i8.clif b/cranelift/filetests/isa/x86/legalize-icmp-i8.clif
new file mode 100644
index 0000000000..41bd27950f
--- /dev/null
+++ b/cranelift/filetests/isa/x86/legalize-icmp-i8.clif
@@ -0,0 +1,19 @@
+test compile
+target x86_64
+
+; regex: V=v\d+
+
+function u0:0(i8, i8) -> i8 fast {
+ebb0(v0: i8, v1: i8):
+    v2 = icmp_imm sle v0, 0
+    ; check: $(e1=$V) = sextend.i32 v0
+    ; nextln: v2 = icmp_imm sle $e1, 0
+    v3 = bint.i8 v2
+    v4 = icmp eq v0, v1
+    ; check: $(e2=$V) = uextend.i32 v0
+    ; nextln: $(e3=$V) = uextend.i32 v1
+    ; nextln: v4 = icmp eq $e2, $e3
+    v5 = bint.i8 v4
+    v6 = iadd v3, v5
+    return v6
+}
diff --git a/cranelift/filetests/isa/x86/legalize-shlr-i8.clif b/cranelift/filetests/isa/x86/legalize-shlr-i8.clif
new file mode 100644
index 0000000000..dbd0da1204
--- /dev/null
+++ b/cranelift/filetests/isa/x86/legalize-shlr-i8.clif
@@ -0,0 +1,24 @@
+test compile
+target x86_64
+
+; regex: V=v\d+
+
+function u0:0(i8, i8) -> i8 fast {
+ebb0(v0: i8, v1: i8):
+    v2 = ishl v0, v1
+    ; check: $(e1=$V) = uextend.i32 v0
+    ; check: $(r1=$V) = ishl $e1, v1
+    ; check v2 = ireduce.i8 $r1
+    v3 = ushr v0, v1
+    ; check: $(e2=$V) = uextend.i32 v0
+    ; check: $(r2=$V) = ushr $e2, v1
+    ; check v2 = ireduce.i8 $r2
+    v4 = sshr v0, v1
+    ; check: $(e3=$V) = sextend.i32 v0
+    ; check: $(r3=$V) = sshr $e3, v1
+    ; check v2 = ireduce.i8 $r3
+
+    v5 = iadd v2, v3
+    v6 = iadd v4, v5
+    return v6
+}
diff --git a/cranelift/filetests/isa/x86/legalize-urem-i8.clif b/cranelift/filetests/isa/x86/legalize-urem-i8.clif
new file mode 100644
index 0000000000..0c66a3f580
--- /dev/null
+++ b/cranelift/filetests/isa/x86/legalize-urem-i8.clif
@@ -0,0 +1,15 @@
+test compile
+target x86_64
+
+; regex: V=v\d+
+
+function u0:0(i8, i8) -> i8 fast {
+ebb0(v0: i8, v1: i8):
+    v2 = urem v0, v1
+    ; check: $(a=$V) = uextend.i32 v0
+    ; nextln: $(b=$V) = uextend.i32 v1
+    ; nextln: $(c=$V) = iconst.i32 0
+    ; nextln: $(V), $(r=$V) = x86_udivmodx $a, $c, $b
+    ; nextln: v2 = ireduce.i8 $r
+    return v2
+}
diff --git a/cranelift/filetests/legalizer/bitrev.clif b/cranelift/filetests/legalizer/bitrev.clif
index 0f75c373a9..b4098b87b4 100644
--- a/cranelift/filetests/legalizer/bitrev.clif
+++ b/cranelift/filetests/legalizer/bitrev.clif
@@ -6,68 +6,125 @@ ebb0(v0: i8):
     v1 = bitrev.i8 v0
     return v1
 }
-; check: v2 = band_imm v0, 170
-; check: v3 = ushr_imm v2, 1
-; check: v4 = band_imm v0, 85
-; check: v5 = ishl_imm v4, 1
-; check: v16 = uextend.i32 v3
-; check: v17 = uextend.i32 v5
-; check: v18 = bor v16, v17
-; check: v6 = ireduce.i8 v18
-; check: v7 = band_imm v6, 204
-; check: v8 = ushr_imm v7, 2
-; check: v9 = band_imm v6, 51
-; check: v10 = ushr_imm v9, 2
-; check: v19 = uextend.i32 v8
-; check: v20 = uextend.i32 v10
-; check: v21 = bor v19, v20
-; check: v11 = ireduce.i8 v21
-; check: v12 = band_imm v11, 240
-; check: v13 = ushr_imm v12, 4
-; check: v14 = band_imm v11, 15
-; check: v15 = ishl_imm v14, 4
-; check: v22 = uextend.i32 v13
-; check: v23 = uextend.i32 v15
-; check: v24 = bor v22, v23
-; check: v1 = ireduce.i8 v24
+; check: v16 = uextend.i32 v0
+; check: v17 = band_imm v16, 170
+; check: v2 = ireduce.i8 v17
+; check: v18 = uextend.i32 v2
+; check: v19 = ushr_imm v18, 1
+; check: v3 = ireduce.i8 v19
+; check: v20 = uextend.i32 v0
+; check: v21 = band_imm v20, 85
+; check: v4 = ireduce.i8 v21
+; check: v22 = uextend.i32 v4
+; check: v23 = ishl_imm v22, 1
+; check: v5 = ireduce.i8 v23
+; check: v24 = uextend.i32 v3
+; check: v25 = uextend.i32 v5
+; check: v26 = bor v24, v25
+; check: v6 = ireduce.i8 v26
+; check: v27 = uextend.i32 v6
+; check: v28 = band_imm v27, 204
+; check: v7 = ireduce.i8 v28
+; check: v29 = uextend.i32 v7
+; check: v30 = ushr_imm v29, 2
+; check: v8 = ireduce.i8 v30
+; check: v31 = uextend.i32 v6
+; check: v32 = band_imm v31, 51
+; check: v9 = ireduce.i8 v32
+; check: v33 = uextend.i32 v9
+; check: v34 = ushr_imm v33, 2
+; check: v10 = ireduce.i8 v34
+; check: v35 = uextend.i32 v8
+; check: v36 = uextend.i32 v10
+; check: v37 = bor v35, v36
+; check: v11 = ireduce.i8 v37
+; check: v38 = uextend.i32 v11
+; check: v39 = band_imm v38, 240
+; check: v12 = ireduce.i8 v39
+; check: v40 = uextend.i32 v12
+; check: v41 = ushr_imm v40, 4
+; check: v13 = ireduce.i8 v41
+; check: v42 = uextend.i32 v11
+; check: v43 = band_imm v42, 15
+; check: v14 = ireduce.i8 v43
+; check: v44 = uextend.i32 v14
+; check: v45 = ishl_imm v44, 4
+; check: v15 = ireduce.i8 v45
+; check: v46 = uextend.i32 v13
+; check: v47 = uextend.i32 v15
+; check: v48 = bor v46, v47
+; check: v1 = ireduce.i8 v48
+; check: return v1
 
 function %reverse_bits_16(i16) -> i16 {
 ebb0(v0: i16):
     v1 = bitrev.i16 v0
     return v1
 }
-; check: v2 = band_imm v0, 0xaaaa
-; check: v3 = ushr_imm v2, 1
-; check: v4 = band_imm v0, 0x5555
-; check: v5 = ishl_imm v4, 1
-; check: v21 = uextend.i32 v3
-; check: v22 = uextend.i32 v5
-; check: v23 = bor v21, v22
-; check: v6 = ireduce.i16 v23
-; check: v7 = band_imm v6, 0xcccc
-; check: v8 = ushr_imm v7, 2
-; check: v9 = band_imm v6, 0x3333
-; check: v10 = ushr_imm v9, 2
-; check: v24 = uextend.i32 v8
-; check: v25 = uextend.i32 v10
-; check: v26 = bor v24, v25
-; check: v11 = ireduce.i16 v26
-; check: v12 = band_imm v11, 0xf0f0
-; check: v13 = ushr_imm v12, 4
-; check: v14 = band_imm v11, 3855
-; check: v15 = ishl_imm v14, 4
-; check: v27 = uextend.i32 v13
-; check: v28 = uextend.i32 v15
-; check: v29 = bor v27, v28
-; check: v16 = ireduce.i16 v29
-; check: v17 = band_imm v16, 0xff00
-; check: v18 = ushr_imm v17, 8
-; check: v19 = band_imm v16, 255
-; check: v20 = ishl_imm v19, 8
-; check: v30 = uextend.i32 v18
-; check: v31 = uextend.i32 v20
-; check: v32 = bor v30, v31
-; check: v1 = ireduce.i16 v32
+; check: v21 = uextend.i32 v0
+; check: v22 = band_imm v21, 0xaaaa
+; check: v2 = ireduce.i16 v22
+; check: v23 = uextend.i32 v2
+; check: v24 = ushr_imm v23, 1
+; check: v3 = ireduce.i16 v24
+; check: v25 = uextend.i32 v0
+; check: v26 = band_imm v25, 0x5555
+; check: v4 = ireduce.i16 v26
+; check: v27 = uextend.i32 v4
+; check: v28 = ishl_imm v27, 1
+; check: v5 = ireduce.i16 v28
+; check: v29 = uextend.i32 v3
+; check: v30 = uextend.i32 v5
+; check: v31 = bor v29, v30
+; check: v6 = ireduce.i16 v31
+; check: v32 = uextend.i32 v6
+; check: v33 = band_imm v32, 0xcccc
+; check: v7 = ireduce.i16 v33
+; check: v34 = uextend.i32 v7
+; check: v35 = ushr_imm v34, 2
+; check: v8 = ireduce.i16 v35
+; check: v36 = uextend.i32 v6
+; check: v37 = band_imm v36, 0x3333
+; check: v9 = ireduce.i16 v37
+; check: v38 = uextend.i32 v9
+; check: v39 = ushr_imm v38, 2
+; check: v10 = ireduce.i16 v39
+; check: v40 = uextend.i32 v8
+; check: v41 = uextend.i32 v10
+; check: v42 = bor v40, v41
+; check: v11 = ireduce.i16 v42
+; check: v43 = uextend.i32 v11
+; check: v44 = band_imm v43, 0xf0f0
+; check: v12 = ireduce.i16 v44
+; check: v45 = uextend.i32 v12
+; check: v46 = ushr_imm v45, 4
+; check: v13 = ireduce.i16 v46
+; check: v47 = uextend.i32 v11
+; check: v48 = band_imm v47, 3855
+; check: v14 = ireduce.i16 v48
+; check: v49 = uextend.i32 v14
+; check: v50 = ishl_imm v49, 4
+; check: v15 = ireduce.i16 v50
+; check: v51 = uextend.i32 v13
+; check: v52 = uextend.i32 v15
+; check: v53 = bor v51, v52
+; check: v16 = ireduce.i16 v53
+; check: v54 = uextend.i32 v16
+; check: v55 = band_imm v54, 0xff00
+; check: v17 = ireduce.i16 v55
+; check: v56 = uextend.i32 v17
+; check: v57 = ushr_imm v56, 8
+; check: v18 = ireduce.i16 v57
+; check: v58 = uextend.i32 v16
+; check: v59 = band_imm v58, 255
+; check: v19 = ireduce.i16 v59
+; check: v60 = uextend.i32 v19
+; check: v61 = ishl_imm v60, 8
+; check: v20 = ireduce.i16 v61
+; check: v62 = uextend.i32 v18
+; check: v63 = uextend.i32 v20
+; check: v64 = bor v62, v63
+; check: v1 = ireduce.i16 v64
 ; check: return v1
 
 function %reverse_bits_32(i32) -> i32 {
diff --git a/cranelift/src/clif-util.rs b/cranelift/src/clif-util.rs
index d1ad95ed3d..b38d4c587a 100755
--- a/cranelift/src/clif-util.rs
+++ b/cranelift/src/clif-util.rs
@@ -217,7 +217,7 @@ fn main() {
                 rest_cmd.is_present("verbose"),
                 &get_vec(rest_cmd.values_of("pass")),
                 target_val,
-                &rest_cmd.value_of("single-file").unwrap().to_string(),
+                rest_cmd.value_of("single-file").unwrap(),
             ).map(|_time| ())
         }
         ("print-cfg", Some(rest_cmd)) => {
@@ -264,7 +264,7 @@ fn main() {
 
             result
         }
-        _ => Err(format!("Invalid subcommand.")),
+        _ => Err("Invalid subcommand.".to_owned()),
     };
 
     if let Err(mut msg) = res_util {
diff --git a/lib/codegen/meta-python/base/legalize.py b/lib/codegen/meta-python/base/legalize.py
index 9f6175f138..ec82ed9d3f 100644
--- a/lib/codegen/meta-python/base/legalize.py
+++ b/lib/codegen/meta-python/base/legalize.py
@@ -30,6 +30,13 @@ from .instructions import bitrev
 from cdsl.ast import Var
 from cdsl.xform import Rtl, XFormGroup
 
+try:
+    from typing import TYPE_CHECKING # noqa
+    if TYPE_CHECKING:
+        from cdsl.instructions import Instruction # noqa
+except ImportError:
+    TYPE_CHECKING = False
+
 
 narrow = XFormGroup('narrow', """
         Legalize instructions by narrowing.
@@ -89,6 +96,7 @@ expand.custom_legalize(insts.stack_store, 'expand_stack_store')
 
 x = Var('x')
 y = Var('y')
+z = Var('z')
 a = Var('a')
 a1 = Var('a1')
 a2 = Var('a2')
@@ -174,6 +182,92 @@ narrow.legalize(
             a << iconcat(al, ah)
         ))
 
+
+def widen_one_arg(signed, op):
+    # type: (bool, Instruction) -> None
+    for int_ty in [types.i8, types.i16]:
+        if signed:
+            widen.legalize(
+                a << op.bind(int_ty)(b),
+                Rtl(
+                    x << sextend.i32(b),
+                    z << op.i32(x),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+        else:
+            widen.legalize(
+                a << op.bind(int_ty)(b),
+                Rtl(
+                    x << uextend.i32(b),
+                    z << op.i32(x),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+
+
+def widen_two_arg(signed, op):
+    # type: (bool, Instruction) -> None
+    for int_ty in [types.i8, types.i16]:
+        if signed:
+            widen.legalize(
+                a << op.bind(int_ty)(b, c),
+                Rtl(
+                    x << sextend.i32(b),
+                    y << sextend.i32(c),
+                    z << op.i32(x, y),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+        else:
+            widen.legalize(
+                a << op.bind(int_ty)(b, c),
+                Rtl(
+                    x << uextend.i32(b),
+                    y << uextend.i32(c),
+                    z << op.i32(x, y),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+
+
+def widen_imm(signed, op):
+    # type: (bool, Instruction) -> None
+    for int_ty in [types.i8, types.i16]:
+        if signed:
+            widen.legalize(
+                a << op.bind(int_ty)(b, c),
+                Rtl(
+                    x << sextend.i32(b),
+                    z << op.i32(x, c),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+        else:
+            widen.legalize(
+                a << op.bind(int_ty)(b, c),
+                Rtl(
+                    x << uextend.i32(b),
+                    z << op.i32(x, c),
+                    a << ireduce.bind(int_ty)(z)
+                ))
+
+
+for binop in [iadd, isub, imul, udiv, urem]:
+    widen_two_arg(False, binop)
+
+widen_two_arg(True, sdiv)
+
+widen_one_arg(False, bnot)
+
+for binop in [iadd_imm, imul_imm, udiv_imm, urem_imm]:
+    widen_imm(False, binop)
+
+for binop in [sdiv_imm, srem_imm]:
+    widen_imm(True, binop)
+
+# bit ops
+for binop in [band, bor, bxor, band_not, bor_not, bxor_not]:
+    widen_two_arg(False, binop)
+
+for binop in [band_imm, bor_imm, bxor_imm]:
+    widen_imm(False, binop)
+
 for int_ty in [types.i8, types.i16]:
     widen.legalize(
         a << iconst.bind(int_ty)(b),
@@ -210,63 +304,6 @@ widen.legalize(
         a << ireduce(b)
     ))
 
-for binop in [iadd, isub, imul, udiv, band, bor, bxor]:
-    for int_ty in [types.i8, types.i16]:
-        widen.legalize(
-            a << binop.bind(int_ty)(x, y),
-            Rtl(
-                b << uextend.i32(x),
-                c << uextend.i32(y),
-                d << binop(b, c),
-                a << ireduce(d)
-            )
-        )
-
-for binop in [sdiv]:
-    for int_ty in [types.i8, types.i16]:
-        widen.legalize(
-            a << binop.bind(int_ty)(x, y),
-            Rtl(
-                b << sextend.i32(x),
-                c << sextend.i32(y),
-                d << binop(b, c),
-                a << ireduce(d)
-            )
-        )
-
-for unop in [bnot]:
-    for int_ty in [types.i8, types.i16]:
-        widen.legalize(
-            a << unop.bind(int_ty)(x),
-            Rtl(
-                b << sextend.i32(x),
-                d << unop(b),
-                a << ireduce(d)
-            )
-        )
-
-for binop in [iadd_imm, imul_imm, udiv_imm]:
-    for int_ty in [types.i8, types.i16]:
-        widen.legalize(
-            a << binop.bind(int_ty)(x, y),
-            Rtl(
-                b << uextend.i32(x),
-                c << binop(b, y),
-                a << ireduce(c)
-            )
-        )
-
-for binop in [sdiv_imm]:
-    for int_ty in [types.i8, types.i16]:
-        widen.legalize(
-            a << binop.bind(int_ty)(x, y),
-            Rtl(
-                b << sextend.i32(x),
-                c << binop(b, y),
-                a << ireduce(c)
-            )
-        )
-
 for int_ty in [types.i8, types.i16]:
     widen.legalize(
         br_table.bind(int_ty)(x, y),
@@ -285,6 +322,72 @@ for int_ty in [types.i8, types.i16]:
         )
     )
 
+for int_ty in [types.i8, types.i16]:
+    for op in [ushr_imm, ishl_imm]:
+        widen.legalize(
+            a << op.bind(int_ty)(b, c),
+            Rtl(
+                x << uextend.i32(b),
+                z << op.i32(x, c),
+                a << ireduce.bind(int_ty)(z)
+            ))
+
+    widen.legalize(
+        a << ishl.bind(int_ty)(b, c),
+        Rtl(
+            x << uextend.i32(b),
+            z << ishl.i32(x, c),
+            a << ireduce.bind(int_ty)(z)
+        ))
+
+    widen.legalize(
+        a << ushr.bind(int_ty)(b, c),
+        Rtl(
+            x << uextend.i32(b),
+            z << ushr.i32(x, c),
+            a << ireduce.bind(int_ty)(z)
+        ))
+
+    widen.legalize(
+        a << sshr.bind(int_ty)(b, c),
+        Rtl(
+            x << sextend.i32(b),
+            z << sshr.i32(x, c),
+            a << ireduce.bind(int_ty)(z)
+        ))
+
+    for w_cc in [
+        intcc.eq, intcc.ne, intcc.ugt, intcc.ult, intcc.uge, intcc.ule
+    ]:
+        widen.legalize(
+            a << insts.icmp_imm.bind(int_ty)(w_cc, b, c),
+            Rtl(
+                x << uextend.i32(b),
+                a << insts.icmp_imm(w_cc, x, c)
+            ))
+        widen.legalize(
+            a << insts.icmp.bind(int_ty)(w_cc, b, c),
+            Rtl(
+                x << uextend.i32(b),
+                y << uextend.i32(c),
+                a << insts.icmp.i32(w_cc, x, y)
+            ))
+    for w_cc in [intcc.sgt, intcc.slt, intcc.sge, intcc.sle]:
+        widen.legalize(
+            a << insts.icmp_imm.bind(int_ty)(w_cc, b, c),
+            Rtl(
+                x << sextend.i32(b),
+                a << insts.icmp_imm(w_cc, x, c)
+            ))
+        widen.legalize(
+            a << insts.icmp.bind(int_ty)(w_cc, b, c),
+            Rtl(
+                x << sextend.i32(b),
+                y << sextend.i32(c),
+                a << insts.icmp(w_cc, x, y)
+            )
+        )
+
 # Expand integer operations with carry for RISC architectures that don't have
 # the flags.
 expand.legalize(
diff --git a/lib/codegen/meta-python/cdsl/predicates.py b/lib/codegen/meta-python/cdsl/predicates.py
index ee7b81f3da..c81173ad5c 100644
--- a/lib/codegen/meta-python/cdsl/predicates.py
+++ b/lib/codegen/meta-python/cdsl/predicates.py
@@ -244,7 +244,7 @@ class FieldPredicate(object):
         """
         # Prepend `field` to the predicate function arguments.
         args = (self.field.rust_name(),) + tuple(map(str, self.args))
-        return 'predicates::{}({})'.format(self.function, ', '.join(args))
+        return '::predicates::{}({})'.format(self.function, ', '.join(args))
 
 
 class IsEqual(FieldPredicate):
diff --git a/lib/codegen/src/ir/dfg.rs b/lib/codegen/src/ir/dfg.rs
index 9a6a22e9fa..bb8ddbe9c4 100644
--- a/lib/codegen/src/ir/dfg.rs
+++ b/lib/codegen/src/ir/dfg.rs
@@ -165,19 +165,18 @@ fn valid_valuedata(data: &ValueData) -> bool {
             return false;
         }
     }
-    return true;
+    true
 }
 
 impl<'a> Iterator for Values<'a> {
     type Item = Value;
 
     fn next(&mut self) -> Option<Self::Item> {
-        return self
-            .inner
+        self.inner
             .by_ref()
             .filter(|kv| valid_valuedata(kv.1))
             .next()
-            .map(|kv| kv.0);
+            .map(|kv| kv.0)
     }
 }
 
diff --git a/lib/codegen/src/isa/riscv/enc_tables.rs b/lib/codegen/src/isa/riscv/enc_tables.rs
index 46b2458b49..5f7c084a67 100644
--- a/lib/codegen/src/isa/riscv/enc_tables.rs
+++ b/lib/codegen/src/isa/riscv/enc_tables.rs
@@ -6,7 +6,6 @@ use isa;
 use isa::constraints::*;
 use isa::enc_tables::*;
 use isa::encoding::RecipeSizing;
-use predicates;
 
 // Include the generated encoding tables:
 // - `LEVEL1_RV32`
diff --git a/lib/codegen/src/isa/x86/enc_tables.rs b/lib/codegen/src/isa/x86/enc_tables.rs
index ebaaa526f7..65b7d7c38e 100644
--- a/lib/codegen/src/isa/x86/enc_tables.rs
+++ b/lib/codegen/src/isa/x86/enc_tables.rs
@@ -10,7 +10,6 @@ use isa;
 use isa::constraints::*;
 use isa::enc_tables::*;
 use isa::encoding::RecipeSizing;
-use predicates;
 
 include!(concat!(env!("OUT_DIR"), "/encoding-x86.rs"));
 include!(concat!(env!("OUT_DIR"), "/legalize-x86.rs"));
diff --git a/lib/filetests/src/lib.rs b/lib/filetests/src/lib.rs
index 24086d88ab..6d48eb9636 100644
--- a/lib/filetests/src/lib.rs
+++ b/lib/filetests/src/lib.rs
@@ -93,7 +93,7 @@ pub fn run(verbose: bool, files: &[String]) -> TestResult {
 ///
 /// Directories are scanned recursively for test cases ending in `.clif`.
 ///
-pub fn run_passes(verbose: bool, passes: &[String], target: &str, file: &String) -> TestResult {
+pub fn run_passes(verbose: bool, passes: &[String], target: &str, file: &str) -> TestResult {
     let mut runner = TestRunner::new(verbose);
 
     let path = Path::new(file);
diff --git a/lib/frontend/Cargo.toml b/lib/frontend/Cargo.toml
index c838682f57..171c158b8e 100644
--- a/lib/frontend/Cargo.toml
+++ b/lib/frontend/Cargo.toml
@@ -12,6 +12,7 @@ readme = "README.md"
 [dependencies]
 cranelift-codegen = { path = "../codegen", version = "0.22.0", default-features = false }
 target-lexicon = { version = "0.0.3", default-features = false }
+log = { version = "0.4.4", default-features = false, features = ["release_max_level_warn"] }
 
 [features]
 default = ["std"]
diff --git a/lib/frontend/src/lib.rs b/lib/frontend/src/lib.rs
index 73c4abe042..1b5eacd939 100644
--- a/lib/frontend/src/lib.rs
+++ b/lib/frontend/src/lib.rs
@@ -179,12 +179,16 @@
 extern crate cranelift_codegen;
 #[cfg(test)]
 extern crate target_lexicon;
+#[macro_use]
+extern crate log;
 
 pub use frontend::{FunctionBuilder, FunctionBuilderContext};
+pub use switch::Switch;
 pub use variable::Variable;
 
 mod frontend;
 mod ssa;
+mod switch;
 mod variable;
 
 #[cfg(not(feature = "std"))]
diff --git a/lib/frontend/src/switch.rs b/lib/frontend/src/switch.rs
new file mode 100644
index 0000000000..e86c49bddb
--- /dev/null
+++ b/lib/frontend/src/switch.rs
@@ -0,0 +1,350 @@
+use cranelift_codegen::ir::condcodes::IntCC;
+use cranelift_codegen::ir::*;
+use frontend::FunctionBuilder;
+use std::collections::HashMap;
+
+type EntryIndex = u64;
+
+/// Unlike with `br_table`, `Switch` cases may be sparse or non-0-based.
+/// They emit efficient code using branches, jump tables, or a combination of both.
+#[derive(Debug)]
+pub struct Switch {
+    cases: HashMap<EntryIndex, Ebb>,
+}
+
+impl Switch {
+    /// Create a new empty switch
+    pub fn new() -> Self {
+        Switch {
+            cases: HashMap::new(),
+        }
+    }
+
+    /// Set a switch entry
+    pub fn set_entry(&mut self, index: EntryIndex, ebb: Ebb) {
+        let prev = self.cases.insert(index, ebb);
+        assert!(
+            prev.is_none(),
+            "Tried to set the same entry {} twice",
+            index
+        );
+    }
+
+    fn collect_contiguous_case_ranges(self) -> Vec<(EntryIndex, Vec<Ebb>)> {
+        debug!("build_contiguous_case_ranges before: {:#?}", self.cases);
+        let mut cases = self.cases.into_iter().collect::<Vec<(_, _)>>();
+        cases.sort_by_key(|&(index, _)| index);
+
+        let mut contiguous_case_ranges: Vec<(EntryIndex, Vec<Ebb>)> = vec![];
+        let mut last_index = None;
+        for (index, ebb) in cases {
+            match last_index {
+                None => contiguous_case_ranges.push((index, vec![])),
+                Some(last_index) => {
+                    if index > last_index + 1 {
+                        contiguous_case_ranges.push((index, vec![]));
+                    }
+                }
+            }
+            contiguous_case_ranges.last_mut().unwrap().1.push(ebb);
+            last_index = Some(index);
+        }
+
+        debug!(
+            "build_contiguous_case_ranges after: {:#?}",
+            contiguous_case_ranges
+        );
+
+        contiguous_case_ranges
+    }
+
+    fn build_search_tree(
+        bx: &mut FunctionBuilder,
+        val: Value,
+        otherwise: Ebb,
+        contiguous_case_ranges: Vec<(EntryIndex, Vec<Ebb>)>,
+    ) -> Vec<(EntryIndex, Ebb, Vec<Ebb>)> {
+        let mut cases_and_jt_ebbs = Vec::new();
+
+        // Avoid allocation in the common case
+        if contiguous_case_ranges.len() <= 3 {
+            Self::build_search_branches(
+                bx,
+                val,
+                otherwise,
+                contiguous_case_ranges,
+                &mut cases_and_jt_ebbs,
+            );
+            return cases_and_jt_ebbs;
+        }
+
+        let mut stack: Vec<(Option<Ebb>, Vec<(EntryIndex, Vec<Ebb>)>)> = Vec::new();
+        stack.push((None, contiguous_case_ranges));
+
+        while let Some((ebb, contiguous_case_ranges)) = stack.pop() {
+            if let Some(ebb) = ebb {
+                bx.switch_to_block(ebb);
+            }
+
+            if contiguous_case_ranges.len() <= 3 {
+                Self::build_search_branches(
+                    bx,
+                    val,
+                    otherwise,
+                    contiguous_case_ranges,
+                    &mut cases_and_jt_ebbs,
+                );
+            } else {
+                let split_point = contiguous_case_ranges.len() / 2;
+                let mut left = contiguous_case_ranges;
+                let right = left.split_off(split_point);
+
+                let left_ebb = bx.create_ebb();
+                let right_ebb = bx.create_ebb();
+
+                let should_take_right_side =
+                    bx.ins()
+                        .icmp_imm(IntCC::UnsignedGreaterThanOrEqual, val, right[0].0 as i64);
+                bx.ins().brnz(should_take_right_side, right_ebb, &[]);
+                bx.ins().jump(left_ebb, &[]);
+
+                stack.push((Some(left_ebb), left));
+                stack.push((Some(right_ebb), right));
+            }
+        }
+
+        cases_and_jt_ebbs
+    }
+
+    fn build_search_branches(
+        bx: &mut FunctionBuilder,
+        val: Value,
+        otherwise: Ebb,
+        contiguous_case_ranges: Vec<(EntryIndex, Vec<Ebb>)>,
+        cases_and_jt_ebbs: &mut Vec<(EntryIndex, Ebb, Vec<Ebb>)>,
+    ) {
+        for (first_index, ebbs) in contiguous_case_ranges.into_iter().rev() {
+            if ebbs.len() == 1 {
+                let is_good_val = bx.ins().icmp_imm(IntCC::Equal, val, first_index as i64);
+                bx.ins().brnz(is_good_val, ebbs[0], &[]);
+            } else {
+                let jt_ebb = bx.create_ebb();
+                let is_good_val =
+                    bx.ins()
+                        .icmp_imm(IntCC::UnsignedGreaterThanOrEqual, val, first_index as i64);
+                bx.ins().brnz(is_good_val, jt_ebb, &[]);
+                cases_and_jt_ebbs.push((first_index, jt_ebb, ebbs));
+            }
+        }
+
+        bx.ins().jump(otherwise, &[]);
+    }
+
+    fn build_jump_tables(
+        bx: &mut FunctionBuilder,
+        val: Value,
+        otherwise: Ebb,
+        cases_and_jt_ebbs: Vec<(EntryIndex, Ebb, Vec<Ebb>)>,
+    ) {
+        for (first_index, jt_ebb, ebbs) in cases_and_jt_ebbs.into_iter().rev() {
+            let mut jt_data = JumpTableData::new();
+            for ebb in ebbs {
+                jt_data.push_entry(ebb);
+            }
+            let jump_table = bx.create_jump_table(jt_data);
+
+            bx.switch_to_block(jt_ebb);
+            let discr = bx.ins().iadd_imm(val, (first_index as i64).wrapping_neg());
+            bx.ins().br_table(discr, jump_table);
+            bx.ins().jump(otherwise, &[]);
+        }
+    }
+
+    /// Build the switch
+    ///
+    /// # Arguments
+    ///
+    /// * The function builder to emit to
+    /// * The value to switch on
+    /// * The default ebb
+    pub fn emit(self, bx: &mut FunctionBuilder, val: Value, otherwise: Ebb) {
+        // FIXME icmp(_imm) doesn't have encodings for i8 and i16 on x86(_64) yet
+        let val = match bx.func.dfg.value_type(val) {
+            types::I8 | types::I16 => bx.ins().uextend(types::I32, val),
+            _ => val,
+        };
+
+        let contiguous_case_ranges = self.collect_contiguous_case_ranges();
+        let cases_and_jt_ebbs = Self::build_search_tree(bx, val, otherwise, contiguous_case_ranges);
+        Self::build_jump_tables(bx, val, otherwise, cases_and_jt_ebbs);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use cranelift_codegen::ir::Function;
+    use frontend::FunctionBuilderContext;
+
+    macro_rules! setup {
+        ($default:expr, [$($index:expr,)*]) => {{
+            let mut func = Function::new();
+            let mut func_ctx = FunctionBuilderContext::new();
+            {
+                let mut bx = FunctionBuilder::new(&mut func, &mut func_ctx);
+                let ebb = bx.create_ebb();
+                bx.switch_to_block(ebb);
+                let val = bx.ins().iconst(types::I8, 0);
+                let mut switch = Switch::new();
+                $(
+                    let ebb = bx.create_ebb();
+                    switch.set_entry($index, ebb);
+                )*
+                switch.emit(&mut bx, val, Ebb::with_number($default).unwrap());
+            }
+            func
+                .to_string()
+                .trim_left_matches("function u0:0() fast {\n")
+                .trim_right_matches("\n}\n")
+                .to_string()
+        }};
+    }
+
+    #[test]
+    fn switch_zero() {
+        let func = setup!(0, [0,]);
+        assert_eq!(
+            func,
+            "ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm eq v1, 0
+    brnz v2, ebb1
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_single() {
+        let func = setup!(0, [1,]);
+        assert_eq!(
+            func,
+            "ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm eq v1, 1
+    brnz v2, ebb1
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_bool() {
+        let func = setup!(0, [0, 1,]);
+        assert_eq!(
+            func,
+            "    jt0 = jump_table ebb1, ebb2
+
+ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm uge v1, 0
+    brnz v2, ebb3
+    jump ebb0
+
+ebb3:
+    v3 = iadd_imm.i32 v1, 0
+    br_table v3, jt0
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_two_gap() {
+        let func = setup!(0, [0, 2,]);
+        assert_eq!(
+            func,
+            "ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm eq v1, 2
+    brnz v2, ebb2
+    v3 = icmp_imm eq v1, 0
+    brnz v3, ebb1
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_many() {
+        let func = setup!(0, [0, 1, 5, 7, 10, 11, 12,]);
+        assert_eq!(
+            func,
+            "    jt0 = jump_table ebb1, ebb2
+    jt1 = jump_table ebb5, ebb6, ebb7
+
+ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm uge v1, 7
+    brnz v2, ebb9
+    jump ebb8
+
+ebb9:
+    v3 = icmp_imm.i32 uge v1, 10
+    brnz v3, ebb10
+    v4 = icmp_imm.i32 eq v1, 7
+    brnz v4, ebb4
+    jump ebb0
+
+ebb8:
+    v5 = icmp_imm.i32 eq v1, 5
+    brnz v5, ebb3
+    v6 = icmp_imm.i32 uge v1, 0
+    brnz v6, ebb11
+    jump ebb0
+
+ebb11:
+    v7 = iadd_imm.i32 v1, 0
+    br_table v7, jt0
+    jump ebb0
+
+ebb10:
+    v8 = iadd_imm.i32 v1, -10
+    br_table v8, jt1
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_min_index_value() {
+        let func = setup!(0, [::std::i64::MIN as u64, 1,]);
+        assert_eq!(
+            func,
+            "ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm eq v1, 0x8000_0000_0000_0000
+    brnz v2, ebb1
+    v3 = icmp_imm eq v1, 1
+    brnz v3, ebb2
+    jump ebb0"
+        );
+    }
+
+    #[test]
+    fn switch_max_index_value() {
+        let func = setup!(0, [::std::i64::MAX as u64, 1,]);
+        assert_eq!(
+            func,
+            "ebb0:
+    v0 = iconst.i8 0
+    v1 = uextend.i32 v0
+    v2 = icmp_imm eq v1, 0x7fff_ffff_ffff_ffff
+    brnz v2, ebb1
+    v3 = icmp_imm eq v1, 1
+    brnz v3, ebb2
+    jump ebb0"
+        )
+    }
+}
diff --git a/lib/wasm/Cargo.toml b/lib/wasm/Cargo.toml
index c36f04e876..bd2c12d46e 100644
--- a/lib/wasm/Cargo.toml
+++ b/lib/wasm/Cargo.toml
@@ -21,7 +21,7 @@ target-lexicon = { version = "0.0.3", default-features = false }
 log = { version = "0.4.4", default-features = false, features = ["release_max_level_warn"] }
 
 [dev-dependencies]
-wabt = "0.5.0"
+wabt = "0.6.0"
 
 [features]
 default = ["std"]