Remove unnecessary extend instructions (#1147)

* remove unnecessary extend instructions

The Wasm i64_extend_i32_u and i64_extend_i32_s instructions are unnecessary in Wasmi bytecode since they can be replaced entirely by the sign-extension instructions. This is possible since Wasmi bytecode is untyped during execution and the only different between those instructions is their effect on the type system.

* add debug_assert

crates/core/src/untyped.rs

@@ -1135,11 +1135,6 @@ impl UntypedVal {
         self.execute_unary(<i32 as ExtendInto<i64>>::extend_into)
     }
 
-    /// Execute `i64.extend_i32_u` Wasm operation.
-    pub fn i64_extend_i32_u(self) -> Self {
-        self.execute_unary(<u32 as ExtendInto<i64>>::extend_into)
-    }
-
     /// Execute `i64.trunc_f32_s` Wasm operation.
     ///
     /// # Errors

crates/wasmi/src/engine/bytecode/construct.rs

@@ -1386,8 +1386,6 @@ constructor_for_unary_instrs! {
     fn i64_extend32_s() -> Self::I64Extend32S;
 
     fn i32_wrap_i64() -> Self::I32WrapI64;
-    fn i64_extend_i32_s() -> Self::I64ExtendI32S;
-    fn i64_extend_i32_u() -> Self::I64ExtendI32U;
 
     fn f32_demote_f64() -> Self::F32DemoteF64;
     fn f64_promote_f32() -> Self::F64PromoteF32;

crates/wasmi/src/engine/bytecode/mod.rs

@@ -2119,10 +2119,6 @@ pub enum Instruction {
 
     /// Wasm `i32.wrap_i64` instruction.
     I32WrapI64(UnaryInstr),
-    /// Wasm `i64.extend_i32_s` instruction.
-    I64ExtendI32S(UnaryInstr),
-    /// Wasm `i64.extend_i32_u` instruction.
-    I64ExtendI32U(UnaryInstr),
 
     /// Wasm `i32.extend8_s` instruction.
     ///

crates/wasmi/src/engine/executor/instrs.rs

@@ -613,8 +613,6 @@ impl<'engine> Executor<'engine> {
                 Instr::I64RotrImm(instr) => self.execute_i64_rotr_imm(instr),
                 Instr::I64RotrImm16Rev(instr) => self.execute_i64_rotr_imm16_rev(instr),
                 Instr::I32WrapI64(instr) => self.execute_i32_wrap_i64(instr),
-                Instr::I64ExtendI32S(instr) => self.execute_i64_extend_i32_s(instr),
-                Instr::I64ExtendI32U(instr) => self.execute_i64_extend_i32_u(instr),
                 Instr::I32Extend8S(instr) => self.execute_i32_extend8_s(instr),
                 Instr::I32Extend16S(instr) => self.execute_i32_extend16_s(instr),
                 Instr::I64Extend8S(instr) => self.execute_i64_extend8_s(instr),

crates/wasmi/src/engine/executor/instrs/conversion.rs

@@ -31,8 +31,6 @@ macro_rules! impl_fallible_conversion_impls {
 impl<'engine> Executor<'engine> {
     impl_conversion_impls! {
         (Instruction::I32WrapI64, execute_i32_wrap_i64, UntypedVal::i32_wrap_i64),
-        (Instruction::I64ExtendI32S, execute_i64_extend_i32_s, UntypedVal::i64_extend_i32_s),
-        (Instruction::I64ExtendI32U, execute_i64_extend_i32_u, UntypedVal::i64_extend_i32_u),
 
         (Instruction::I32TruncSatF32S, execute_i32_trunc_sat_f32_s, UntypedVal::i32_trunc_sat_f32_s),
         (Instruction::I32TruncSatF32U, execute_i32_trunc_sat_f32_u, UntypedVal::i32_trunc_sat_f32_u),

crates/wasmi/src/engine/translator/mod.rs

@@ -2520,6 +2520,25 @@ impl FuncTranslator {
         Ok(())
     }
 
+    /// Translates a Wasm `i64.extend_i32_u` instruction.
+    fn translate_i64_extend_i32_u(&mut self) -> Result<(), Error> {
+        bail_unreachable!(self);
+        if let TypedProvider::Register(_) = self.alloc.stack.peek() {
+            // Nothing to do.
+            //
+            // We try to not manipulate the emulation stack if not needed.
+            return Ok(());
+        }
+        // Case: At this point we know that the top-most stack item is a constant value.
+        //       We pop it, change its type and push it back onto the stack.
+        let TypedProvider::Const(value) = self.alloc.stack.pop() else {
+            panic!("the top-most stack item was asserted to be a constant value but a register was found")
+        };
+        debug_assert_eq!(value.ty(), ValType::I32);
+        self.alloc.stack.push_const(u64::from(u32::from(value)));
+        Ok(())
+    }
+
     /// Translates an unconditional `return` instruction.
     fn translate_return(&mut self) -> Result<(), Error> {
         let fuel_info = self.fuel_info();

crates/wasmi/src/engine/translator/relink_result.rs

@@ -497,8 +497,6 @@ impl Instruction {
             I::I64RemUImm16Rev(instr) => relink_simple(instr, new_result, old_result),
 
             I::I32WrapI64(instr) |
-            I::I64ExtendI32S(instr) |
-            I::I64ExtendI32U(instr) |
             I::I32TruncF32S(instr) |
             I::I32TruncF32U(instr) |
             I::I32TruncF64S(instr) |

crates/wasmi/src/engine/translator/tests/op/unary/conversion.rs

@@ -32,7 +32,7 @@ mod i64_extend_i32_s {
     #[test]
     #[cfg_attr(miri, ignore)]
     fn reg() {
-        conversion_reg::<i32, i64>(OP, Instruction::i64_extend_i32_s);
+        conversion_reg::<i32, i64>(OP, Instruction::i64_extend32_s);
     }
 
     #[test]
@@ -57,7 +57,8 @@ mod i64_extend_i32_u {
     #[test]
     #[cfg_attr(miri, ignore)]
     fn reg() {
-        conversion_reg::<i32, i64>(OP, Instruction::i64_extend_i32_u);
+        let expected = [Instruction::return_reg(0)];
+        conversion_reg_with::<i32, i64, _>(OP, expected)
     }
 
     #[test]

crates/wasmi/src/engine/translator/typed_value.rs

@@ -308,7 +308,6 @@ impl TypedVal {
 
         fn i32_wrap_i64(i64) -> i32;
         fn i64_extend_i32_s(i32) -> i64;
-        fn i64_extend_i32_u(i32) -> i64;
 
         fn f32_demote_f64(f64) -> f32;
         fn f64_promote_f32(f32) -> f64;

crates/wasmi/src/engine/translator/visit.rs

@@ -3049,11 +3049,11 @@ impl<'a> VisitOperator<'a> for FuncTranslator {
     }
 
     fn visit_i64_extend_i32_s(&mut self) -> Self::Output {
-        self.translate_unary(Instruction::i64_extend_i32_s, TypedVal::i64_extend_i32_s)
+        self.translate_unary(Instruction::i64_extend32_s, TypedVal::i64_extend_i32_s)
     }
 
     fn visit_i64_extend_i32_u(&mut self) -> Self::Output {
-        self.translate_unary(Instruction::i64_extend_i32_u, TypedVal::i64_extend_i32_u)
+        self.translate_i64_extend_i32_u()
     }
 
     fn visit_i64_trunc_f32_s(&mut self) -> Self::Output {

crates/wasmi/src/engine/translator/visit_register.rs

@@ -523,8 +523,6 @@ impl VisitInputRegisters for Instruction {
             Instruction::F32CopysignImm(instr) => instr.visit_input_registers(f),
             Instruction::F64CopysignImm(instr) => instr.visit_input_registers(f),
             Instruction::I32WrapI64(instr) => instr.visit_input_registers(f),
-            Instruction::I64ExtendI32S(instr) => instr.visit_input_registers(f),
-            Instruction::I64ExtendI32U(instr) => instr.visit_input_registers(f),
             Instruction::I32TruncF32S(instr) => instr.visit_input_registers(f),
             Instruction::I32TruncF32U(instr) => instr.visit_input_registers(f),
             Instruction::I32TruncF64S(instr) => instr.visit_input_registers(f),