🚧 Implement the operand swappers

example/test2.wast

@@ -23,7 +23,7 @@
                 (i32.const 1)
                 (i32.const 2)
             )
-            (i32.add
+            (i32.lt_s
                 (i32.const 4)
                 (i32.const 3)
             )

src/kyut/watermarker/OperandSwappingWatermarker.cpp

@@ -51,6 +51,265 @@ namespace kyut::watermarker {
             write = 2,
         };
 
+        std::optional<wasm::BinaryOp> getSwappedPredicate(wasm::BinaryOp op) {
+            switch (op) {
+                // Commutative instructions
+            case wasm::AddInt32:
+            case wasm::MulInt32:
+            case wasm::AndInt32:
+            case wasm::OrInt32:
+            case wasm::XorInt32:
+            case wasm::EqInt32:
+            case wasm::NeInt32:
+
+            case wasm::AddInt64:
+            case wasm::MulInt64:
+            case wasm::AndInt64:
+            case wasm::OrInt64:
+            case wasm::XorInt64:
+            case wasm::EqInt64:
+            case wasm::NeInt64:
+
+            case wasm::AddFloat32:
+            case wasm::MulFloat32:
+            case wasm::MinFloat32:
+            case wasm::MaxFloat32:
+            case wasm::EqFloat32:
+            case wasm::NeFloat32:
+
+            case wasm::AddFloat64:
+            case wasm::MulFloat64:
+            case wasm::MinFloat64:
+            case wasm::MaxFloat64:
+            case wasm::EqFloat64:
+            case wasm::NeFloat64:
+                return op;
+
+                // Comparators
+            case wasm::LtSInt32:
+                return wasm::GtSInt32;
+            case wasm::LtUInt32:
+                return wasm::GtUInt32;
+            case wasm::LeSInt32:
+                return wasm::GeSInt32;
+            case wasm::LeUInt32:
+                return wasm::GeUInt32;
+            case wasm::GtSInt32:
+                return wasm::LtSInt32;
+            case wasm::GtUInt32:
+                return wasm::LtUInt32;
+            case wasm::GeSInt32:
+                return wasm::LeSInt32;
+            case wasm::GeUInt32:
+                return wasm::LeUInt32;
+
+            case wasm::LtSInt64:
+                return wasm::GtSInt64;
+            case wasm::LtUInt64:
+                return wasm::GtUInt64;
+            case wasm::LeSInt64:
+                return wasm::GeSInt64;
+            case wasm::LeUInt64:
+                return wasm::GeUInt64;
+            case wasm::GtSInt64:
+                return wasm::LtSInt64;
+            case wasm::GtUInt64:
+                return wasm::LtUInt64;
+            case wasm::GeSInt64:
+                return wasm::LeSInt64;
+            case wasm::GeUInt64:
+                return wasm::LeUInt64;
+
+            case wasm::LtFloat32:
+                return wasm::GtFloat32;
+            case wasm::LeFloat32:
+                return wasm::GeFloat32;
+            case wasm::GtFloat32:
+                return wasm::LtFloat32;
+            case wasm::GeFloat32:
+                return wasm::LeFloat32;
+
+            case wasm::LtFloat64:
+                return wasm::GtFloat64;
+            case wasm::LeFloat64:
+                return wasm::GeFloat64;
+            case wasm::GtFloat64:
+                return wasm::LtFloat64;
+            case wasm::GeFloat64:
+                return wasm::LeFloat64;
+
+                // Noncommutative instructions
+            case wasm::SubInt32:
+            case wasm::DivSInt32:
+            case wasm::DivUInt32:
+            case wasm::RemSInt32:
+            case wasm::RemUInt32:
+            case wasm::ShlInt32:
+            case wasm::ShrUInt32:
+            case wasm::ShrSInt32:
+            case wasm::RotLInt32:
+            case wasm::RotRInt32:
+
+            case wasm::SubInt64:
+            case wasm::DivSInt64:
+            case wasm::DivUInt64:
+            case wasm::RemSInt64:
+            case wasm::RemUInt64:
+            case wasm::ShlInt64:
+            case wasm::ShrUInt64:
+            case wasm::ShrSInt64:
+            case wasm::RotLInt64:
+            case wasm::RotRInt64:
+
+            case wasm::SubFloat32:
+            case wasm::DivFloat32:
+            case wasm::CopySignFloat32:
+
+            case wasm::SubFloat64:
+            case wasm::DivFloat64:
+            case wasm::CopySignFloat64:
+                return std::nullopt;
+
+            // Commutative SIMD instructions
+            case wasm::EqVecI8x16:
+            case wasm::NeVecI8x16:
+            case wasm::EqVecI16x8:
+            case wasm::NeVecI16x8:
+            case wasm::EqVecI32x4:
+            case wasm::NeVecI32x4:
+            case wasm::EqVecF32x4:
+            case wasm::NeVecF32x4:
+            case wasm::EqVecF64x2:
+            case wasm::NeVecF64x2:
+            case wasm::AndVec128:
+            case wasm::OrVec128:
+            case wasm::XorVec128:
+            case wasm::AddVecI8x16:
+            case wasm::AddSatSVecI8x16:
+            case wasm::AddSatUVecI8x16:
+            case wasm::MulVecI8x16:
+            case wasm::AddVecI16x8:
+            case wasm::AddSatSVecI16x8:
+            case wasm::AddSatUVecI16x8:
+            case wasm::MulVecI16x8:
+            case wasm::AddVecI32x4:
+            case wasm::MulVecI32x4:
+            case wasm::AddVecI64x2:
+            case wasm::AddVecF32x4:
+            case wasm::MulVecF32x4:
+            case wasm::MinVecF32x4:
+            case wasm::MaxVecF32x4:
+            case wasm::AddVecF64x2:
+            case wasm::MulVecF64x2:
+            case wasm::MinVecF64x2:
+            case wasm::MaxVecF64x2:
+                return op;
+
+            // SIMD comparators
+            case wasm::LtSVecI8x16:
+                return wasm::GtSVecI8x16;
+            case wasm::LtUVecI8x16:
+                return wasm::GtUVecI8x16;
+            case wasm::GtSVecI8x16:
+                return wasm::LtSVecI8x16;
+            case wasm::GtUVecI8x16:
+                return wasm::LtUVecI8x16;
+            case wasm::LeSVecI8x16:
+                return wasm::GeSVecI8x16;
+            case wasm::LeUVecI8x16:
+                return wasm::GeUVecI8x16;
+            case wasm::GeSVecI8x16:
+                return wasm::LeSVecI8x16;
+            case wasm::GeUVecI8x16:
+                return wasm::LeUVecI8x16;
+
+            case wasm::LtSVecI16x8:
+                return wasm::GtSVecI16x8;
+            case wasm::LtUVecI16x8:
+                return wasm::GtUVecI16x8;
+            case wasm::GtSVecI16x8:
+                return wasm::LtSVecI16x8;
+            case wasm::GtUVecI16x8:
+                return wasm::LtUVecI16x8;
+            case wasm::LeSVecI16x8:
+                return wasm::GeSVecI16x8;
+            case wasm::LeUVecI16x8:
+                return wasm::GeUVecI16x8;
+            case wasm::GeSVecI16x8:
+                return wasm::LeSVecI16x8;
+            case wasm::GeUVecI16x8:
+                return wasm::LeUVecI16x8;
+
+            case wasm::LtSVecI32x4:
+                return wasm::GtSVecI32x4;
+            case wasm::LtUVecI32x4:
+                return wasm::GtUVecI32x4;
+            case wasm::GtSVecI32x4:
+                return wasm::LtSVecI32x4;
+            case wasm::GtUVecI32x4:
+                return wasm::LtUVecI32x4;
+            case wasm::LeSVecI32x4:
+                return wasm::GeSVecI32x4;
+            case wasm::LeUVecI32x4:
+                return wasm::GeUVecI32x4;
+            case wasm::GeSVecI32x4:
+                return wasm::LeSVecI32x4;
+            case wasm::GeUVecI32x4:
+                return wasm::LeUVecI32x4;
+
+            case wasm::LtVecF32x4:
+                return wasm::GtVecF32x4;
+            case wasm::GtVecF32x4:
+                return wasm::LtVecF32x4;
+            case wasm::LeVecF32x4:
+                return wasm::GeVecF32x4;
+            case wasm::GeVecF32x4:
+                return wasm::LeVecF32x4;
+
+            case wasm::LtVecF64x2:
+                return wasm::GtVecF64x2;
+            case wasm::GtVecF64x2:
+                return wasm::LtVecF64x2;
+            case wasm::LeVecF64x2:
+                return wasm::GeVecF64x2;
+            case wasm::GeVecF64x2:
+                return wasm::LeVecF64x2;
+
+                // Noncommutative SIMD instructions
+            case wasm::SubVecI8x16:
+            case wasm::SubSatSVecI8x16:
+            case wasm::SubSatUVecI8x16:
+            case wasm::SubVecI16x8:
+            case wasm::SubSatSVecI16x8:
+            case wasm::SubSatUVecI16x8:
+            case wasm::SubVecI32x4:
+            case wasm::SubVecI64x2:
+            case wasm::SubVecF32x4:
+            case wasm::DivVecF32x4:
+            case wasm::SubVecF64x2:
+            case wasm::DivVecF64x2:
+                return std::nullopt;
+
+            default:
+                WASM_UNREACHABLE();
+            }
+        }
+
+        bool isCommutative(wasm::BinaryOp op) {
+            return getSwappedPredicate(op).has_value();
+        }
+
+        bool swapOperands(wasm::Binary &expr) {
+            if (const auto newOp = getSwappedPredicate(expr.op)) {
+                expr.op = *newOp;
+                std::swap(expr.left, expr.right);
+
+                return true;
+            }
+
+            return false;
+        }
+
         // Watermark embedder
         SideEffect embedExpression(wasm::Expression *expr, CircularBitStreamReader &stream);
 
@@ -148,8 +407,18 @@ namespace kyut::watermarker {
         }
 
         SideEffect embedBinary(wasm::Binary &expr, CircularBitStreamReader &stream) {
+            if (!isCommutative(expr.op)) {
+                // The operands of noncommutative instructions cannot be swapped
+                return (std::max)(embedExpression(expr.left, stream), embedExpression(expr.right, stream));
+            }
+
             // TODO: implement watermarking
-            return (std::max)(embedExpression(expr.left, stream), embedExpression(expr.right, stream));
+            const auto leftSideEffect = embedExpression(expr.left, stream);
+            const auto rightSideEffect = embedExpression(expr.right, stream);
+
+            (void)swapOperands;
+
+            return (std::max)(leftSideEffect, rightSideEffect);
         }
 
         SideEffect embedSelect(wasm::Select &expr, CircularBitStreamReader &stream) {