diff --git a/lib/singlepass-backend/src/codegen_x64.rs b/lib/singlepass-backend/src/codegen_x64.rs
index 7e3a9ed5f..c2543b987 100644
--- a/lib/singlepass-backend/src/codegen_x64.rs
+++ b/lib/singlepass-backend/src/codegen_x64.rs
@@ -2341,18 +2341,109 @@ impl FunctionCodeGenerator<CodegenError> for X64FunctionCode {
                 Condition::Equal,
                 Location::Imm32(0),
             ),
-            Operator::I32Clz => Self::emit_xcnt_i32(
-                a,
-                &mut self.machine,
-                &mut self.value_stack,
-                Assembler::emit_lzcnt,
-            ),
-            Operator::I32Ctz => Self::emit_xcnt_i32(
-                a,
-                &mut self.machine,
-                &mut self.value_stack,
-                Assembler::emit_tzcnt,
-            ),
+            Operator::I32Clz => {
+                let loc =
+                    get_location_released(a, &mut self.machine, self.value_stack.pop().unwrap());
+                let src = match loc {
+                    Location::Imm32(_) | Location::Memory(_, _) => {
+                        let tmp = self.machine.acquire_temp_gpr().unwrap();
+                        a.emit_mov(Size::S32, loc, Location::GPR(tmp));
+                        tmp
+                    }
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let ret = self.machine.acquire_locations(
+                    a,
+                    &[(WpType::I32, MachineValue::WasmStack(self.value_stack.len()))],
+                    false,
+                )[0];
+                self.value_stack.push(ret);
+
+                let dst = match ret {
+                    Location::Memory(_, _) => self.machine.acquire_temp_gpr().unwrap(),
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let zero_path = a.get_label();
+                let end = a.get_label();
+
+                a.emit_test_gpr_64(src);
+                a.emit_jmp(Condition::Equal, zero_path);
+                a.emit_bsr(Size::S32, Location::GPR(src), Location::GPR(dst));
+                a.emit_xor(Size::S32, Location::Imm32(31), Location::GPR(dst));
+                a.emit_jmp(Condition::None, end);
+                a.emit_label(zero_path);
+                a.emit_mov(Size::S32, Location::Imm32(32), Location::GPR(dst));
+                a.emit_label(end);
+
+                match loc {
+                    Location::Imm32(_) | Location::Memory(_, _) => {
+                        self.machine.release_temp_gpr(src);
+                    }
+                    _ => {}
+                };
+                match ret {
+                    Location::Memory(_, _) => {
+                        a.emit_mov(Size::S32, Location::GPR(dst), ret);
+                        self.machine.release_temp_gpr(dst);
+                    }
+                    _ => {}
+                };
+            }
+            Operator::I32Ctz => {
+                let loc =
+                    get_location_released(a, &mut self.machine, self.value_stack.pop().unwrap());
+                let src = match loc {
+                    Location::Imm32(_) | Location::Memory(_, _) => {
+                        let tmp = self.machine.acquire_temp_gpr().unwrap();
+                        a.emit_mov(Size::S32, loc, Location::GPR(tmp));
+                        tmp
+                    }
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let ret = self.machine.acquire_locations(
+                    a,
+                    &[(WpType::I32, MachineValue::WasmStack(self.value_stack.len()))],
+                    false,
+                )[0];
+                self.value_stack.push(ret);
+
+                let dst = match ret {
+                    Location::Memory(_, _) => self.machine.acquire_temp_gpr().unwrap(),
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let zero_path = a.get_label();
+                let end = a.get_label();
+
+                a.emit_test_gpr_64(src);
+                a.emit_jmp(Condition::Equal, zero_path);
+                a.emit_bsf(Size::S32, Location::GPR(src), Location::GPR(dst));
+                a.emit_jmp(Condition::None, end);
+                a.emit_label(zero_path);
+                a.emit_mov(Size::S32, Location::Imm32(32), Location::GPR(dst));
+                a.emit_label(end);
+
+                match loc {
+                    Location::Imm32(_) | Location::Memory(_, _) => {
+                        self.machine.release_temp_gpr(src);
+                    }
+                    _ => {}
+                };
+                match ret {
+                    Location::Memory(_, _) => {
+                        a.emit_mov(Size::S32, Location::GPR(dst), ret);
+                        self.machine.release_temp_gpr(dst);
+                    }
+                    _ => {}
+                };
+            }
             Operator::I32Popcnt => Self::emit_xcnt_i32(
                 a,
                 &mut self.machine,
@@ -2632,18 +2723,109 @@ impl FunctionCodeGenerator<CodegenError> for X64FunctionCode {
                 Condition::Equal,
                 Location::Imm64(0),
             ),
-            Operator::I64Clz => Self::emit_xcnt_i64(
-                a,
-                &mut self.machine,
-                &mut self.value_stack,
-                Assembler::emit_lzcnt,
-            ),
-            Operator::I64Ctz => Self::emit_xcnt_i64(
-                a,
-                &mut self.machine,
-                &mut self.value_stack,
-                Assembler::emit_tzcnt,
-            ),
+            Operator::I64Clz => {
+                let loc =
+                    get_location_released(a, &mut self.machine, self.value_stack.pop().unwrap());
+                let src = match loc {
+                    Location::Imm64(_) | Location::Imm32(_) | Location::Memory(_, _) => {
+                        let tmp = self.machine.acquire_temp_gpr().unwrap();
+                        a.emit_mov(Size::S64, loc, Location::GPR(tmp));
+                        tmp
+                    }
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let ret = self.machine.acquire_locations(
+                    a,
+                    &[(WpType::I64, MachineValue::WasmStack(self.value_stack.len()))],
+                    false,
+                )[0];
+                self.value_stack.push(ret);
+
+                let dst = match ret {
+                    Location::Memory(_, _) => self.machine.acquire_temp_gpr().unwrap(),
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let zero_path = a.get_label();
+                let end = a.get_label();
+
+                a.emit_test_gpr_64(src);
+                a.emit_jmp(Condition::Equal, zero_path);
+                a.emit_bsr(Size::S64, Location::GPR(src), Location::GPR(dst));
+                a.emit_xor(Size::S64, Location::Imm32(63), Location::GPR(dst));
+                a.emit_jmp(Condition::None, end);
+                a.emit_label(zero_path);
+                a.emit_mov(Size::S64, Location::Imm32(64), Location::GPR(dst));
+                a.emit_label(end);
+
+                match loc {
+                    Location::Imm64(_) | Location::Imm32(_) | Location::Memory(_, _) => {
+                        self.machine.release_temp_gpr(src);
+                    }
+                    _ => {}
+                };
+                match ret {
+                    Location::Memory(_, _) => {
+                        a.emit_mov(Size::S64, Location::GPR(dst), ret);
+                        self.machine.release_temp_gpr(dst);
+                    }
+                    _ => {}
+                };
+            }
+            Operator::I64Ctz => {
+                let loc =
+                    get_location_released(a, &mut self.machine, self.value_stack.pop().unwrap());
+                let src = match loc {
+                    Location::Imm64(_) | Location::Imm32(_) | Location::Memory(_, _) => {
+                        let tmp = self.machine.acquire_temp_gpr().unwrap();
+                        a.emit_mov(Size::S64, loc, Location::GPR(tmp));
+                        tmp
+                    }
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let ret = self.machine.acquire_locations(
+                    a,
+                    &[(WpType::I64, MachineValue::WasmStack(self.value_stack.len()))],
+                    false,
+                )[0];
+                self.value_stack.push(ret);
+
+                let dst = match ret {
+                    Location::Memory(_, _) => self.machine.acquire_temp_gpr().unwrap(),
+                    Location::GPR(reg) => reg,
+                    _ => unreachable!(),
+                };
+
+                let zero_path = a.get_label();
+                let end = a.get_label();
+
+                a.emit_test_gpr_64(src);
+                a.emit_jmp(Condition::Equal, zero_path);
+                a.emit_bsf(Size::S64, Location::GPR(src), Location::GPR(dst));
+                a.emit_jmp(Condition::None, end);
+                a.emit_label(zero_path);
+                a.emit_mov(Size::S64, Location::Imm32(64), Location::GPR(dst));
+                a.emit_label(end);
+
+                match loc {
+                    Location::Imm64(_) | Location::Imm32(_) | Location::Memory(_, _) => {
+                        self.machine.release_temp_gpr(src);
+                    }
+                    _ => {}
+                };
+                match ret {
+                    Location::Memory(_, _) => {
+                        a.emit_mov(Size::S64, Location::GPR(dst), ret);
+                        self.machine.release_temp_gpr(dst);
+                    }
+                    _ => {}
+                };
+            }
             Operator::I64Popcnt => Self::emit_xcnt_i64(
                 a,
                 &mut self.machine,
diff --git a/lib/singlepass-backend/src/emitter_x64.rs b/lib/singlepass-backend/src/emitter_x64.rs
index 2e747f7ec..a7543688a 100644
--- a/lib/singlepass-backend/src/emitter_x64.rs
+++ b/lib/singlepass-backend/src/emitter_x64.rs
@@ -90,8 +90,8 @@ pub trait Emitter {
     fn emit_ror(&mut self, sz: Size, src: Location, dst: Location);
     fn emit_and(&mut self, sz: Size, src: Location, dst: Location);
     fn emit_or(&mut self, sz: Size, src: Location, dst: Location);
-    fn emit_lzcnt(&mut self, sz: Size, src: Location, dst: Location);
-    fn emit_tzcnt(&mut self, sz: Size, src: Location, dst: Location);
+    fn emit_bsr(&mut self, sz: Size, src: Location, dst: Location);
+    fn emit_bsf(&mut self, sz: Size, src: Location, dst: Location);
     fn emit_popcnt(&mut self, sz: Size, src: Location, dst: Location);
     fn emit_movzx(&mut self, sz_src: Size, src: Location, sz_dst: Size, dst: Location);
     fn emit_movsx(&mut self, sz_src: Size, src: Location, sz_dst: Size, dst: Location);
@@ -753,17 +753,17 @@ impl Emitter for Assembler {
             panic!("singlepass can't emit OR {:?} {:?} {:?}", sz, src, dst)
         });
     }
-    fn emit_lzcnt(&mut self, sz: Size, src: Location, dst: Location) {
-        binop_gpr_gpr!(lzcnt, self, sz, src, dst, {
-            binop_mem_gpr!(lzcnt, self, sz, src, dst, {
-                panic!("singlepass can't emit LZCNT {:?} {:?} {:?}", sz, src, dst)
+    fn emit_bsr(&mut self, sz: Size, src: Location, dst: Location) {
+        binop_gpr_gpr!(bsr, self, sz, src, dst, {
+            binop_mem_gpr!(bsr, self, sz, src, dst, {
+                panic!("singlepass can't emit BSR {:?} {:?} {:?}", sz, src, dst)
             })
         });
     }
-    fn emit_tzcnt(&mut self, sz: Size, src: Location, dst: Location) {
-        binop_gpr_gpr!(tzcnt, self, sz, src, dst, {
-            binop_mem_gpr!(tzcnt, self, sz, src, dst, {
-                panic!("singlepass can't emit TZCNT {:?} {:?} {:?}", sz, src, dst)
+    fn emit_bsf(&mut self, sz: Size, src: Location, dst: Location) {
+        binop_gpr_gpr!(bsf, self, sz, src, dst, {
+            binop_mem_gpr!(bsf, self, sz, src, dst, {
+                panic!("singlepass can't emit BSF {:?} {:?} {:?}", sz, src, dst)
             })
         });
     }
diff --git a/lib/spectests/tests/excludes.txt b/lib/spectests/tests/excludes.txt
index dee265684..6cd94753b 100644
--- a/lib/spectests/tests/excludes.txt
+++ b/lib/spectests/tests/excludes.txt
@@ -902,15 +902,6 @@ singlepass:fail:i32.wast:99 # AssertTrap - expected trap, got Runtime:Error unkn
 singlepass:fail:i32.wast:100 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i32.wast:120 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i32.wast:121 # AssertTrap - expected trap, got Runtime:Error unknown error
-singlepass:fail:i32.wast:242 # AssertReturn - result I32(31) ("0x1f") does not match expected I32(0) ("0x0")
-singlepass:fail:i32.wast:243 # AssertReturn - result I32(0) ("0x0") does not match expected I32(32) ("0x20")
-singlepass:fail:i32.wast:244 # AssertReturn - result I32(15) ("0xf") does not match expected I32(16) ("0x10")
-singlepass:fail:i32.wast:245 # AssertReturn - result I32(7) ("0x7") does not match expected I32(24) ("0x18")
-singlepass:fail:i32.wast:246 # AssertReturn - result I32(31) ("0x1f") does not match expected I32(0) ("0x0")
-singlepass:fail:i32.wast:247 # AssertReturn - result I32(0) ("0x0") does not match expected I32(31) ("0x1f")
-singlepass:fail:i32.wast:248 # AssertReturn - result I32(1) ("0x1") does not match expected I32(30) ("0x1e")
-singlepass:fail:i32.wast:249 # AssertReturn - result I32(30) ("0x1e") does not match expected I32(1) ("0x1")
-singlepass:fail:i32.wast:252 # AssertReturn - result I32(0) ("0x0") does not match expected I32(32) ("0x20")
 singlepass:fail:i64.wast:62 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i64.wast:63 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i64.wast:64 # AssertTrap - expected trap, got Runtime:Error unknown error
@@ -920,15 +911,6 @@ singlepass:fail:i64.wast:99 # AssertTrap - expected trap, got Runtime:Error unkn
 singlepass:fail:i64.wast:100 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i64.wast:120 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:i64.wast:121 # AssertTrap - expected trap, got Runtime:Error unknown error
-singlepass:fail:i64.wast:242 # AssertReturn - result I64(63) ("0x3f") does not match expected I64(0) ("0x0")
-singlepass:fail:i64.wast:243 # AssertReturn - result I64(0) ("0x0") does not match expected I64(64) ("0x40")
-singlepass:fail:i64.wast:244 # AssertReturn - result I64(15) ("0xf") does not match expected I64(48) ("0x30")
-singlepass:fail:i64.wast:245 # AssertReturn - result I64(7) ("0x7") does not match expected I64(56) ("0x38")
-singlepass:fail:i64.wast:246 # AssertReturn - result I64(63) ("0x3f") does not match expected I64(0) ("0x0")
-singlepass:fail:i64.wast:247 # AssertReturn - result I64(0) ("0x0") does not match expected I64(63) ("0x3f")
-singlepass:fail:i64.wast:248 # AssertReturn - result I64(1) ("0x1") does not match expected I64(62) ("0x3e")
-singlepass:fail:i64.wast:249 # AssertReturn - result I64(62) ("0x3e") does not match expected I64(1) ("0x1")
-singlepass:fail:i64.wast:252 # AssertReturn - result I64(0) ("0x0") does not match expected I64(64) ("0x40")
 singlepass:fail:if.wast:440 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:imports.wast:283 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:imports.wast:286 # AssertTrap - expected trap, got Runtime:Error unknown error
@@ -977,7 +959,6 @@ singlepass:fail:linking.wast:236 # AssertTrap - expected trap, got Runtime:Error
 singlepass:fail:linking.wast:248 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:linking.wast:387 # AssertReturn - result I32(0) ("0x0") does not match expected I32(104) ("0x68")
 singlepass:fail:linking.wast:388 # AssertReturn - Call failed RuntimeError: unknown error
-singlepass:fail:load.wast:201 # AssertReturn - result I32(0) ("0x0") does not match expected I32(32) ("0x20")
 singlepass:fail:memory_grow.wast:15 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_grow.wast:16 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_grow.wast:17 # AssertTrap - expected trap, got Runtime:Error unknown error
@@ -985,7 +966,6 @@ singlepass:fail:memory_grow.wast:18 # AssertTrap - expected trap, got Runtime:Er
 singlepass:fail:memory_grow.wast:24 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_grow.wast:25 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_grow.wast:286 # AssertTrap - expected trap, got Runtime:Error unknown error
-singlepass:fail:memory_grow.wast:299 # AssertReturn - result I32(0) ("0x0") does not match expected I32(31) ("0x1f")
 singlepass:fail:memory_trap.wast:23 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_trap.wast:24 # AssertTrap - expected trap, got Runtime:Error unknown error
 singlepass:fail:memory_trap.wast:25 # AssertTrap - expected trap, got Runtime:Error unknown error