refactor: inline fields in arithmetic operations

jadx-core/src/main/java/jadx/core/dex/instructions/ArithNode.java

@@ -51,6 +51,7 @@ public class ArithNode extends InsnNode {
 		addArg(b);
 	}
 
+	// TODO: remove result for one arg insn, this will simplify processing and allow to remove FieldArg
 	public ArithNode(ArithOp op, RegisterArg res, InsnArg a) {
 		this(op, res, res, a);
 		add(AFlag.ARITH_ONEARG);

jadx-core/src/main/java/jadx/core/dex/visitors/SimplifyVisitor.java

@@ -4,6 +4,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -39,6 +40,7 @@ import jadx.core.dex.regions.conditions.IfCondition;
 import jadx.core.utils.BlockUtils;
 import jadx.core.utils.InsnList;
 import jadx.core.utils.InsnRemover;
+import jadx.core.utils.exceptions.JadxRuntimeException;
 
 public class SimplifyVisitor extends AbstractVisitor {
 
@@ -59,21 +61,16 @@ public class SimplifyVisitor extends AbstractVisitor {
 		for (int i = 0; i < list.size(); i++) {
 			InsnNode insn = list.get(i);
 			int insnCount = list.size();
-			InsnNode modInsn = simplifyInsn(mth, insn);
+			InsnNode modInsn = simplifyInsn(mth, block, insn);
 			if (modInsn != null) {
-				if (i != 0 && modInsn.contains(AFlag.ARITH_ONEARG)) {
-					InsnNode mergedNode = simplifyOneArgConsecutive(
-							list.get(i - 1), list.get(i), (ArithNode) modInsn);
-
-					if (mergedNode != null) {
-						list.remove(i - 1);
-						modInsn = mergedNode;
-						i--;
-					}
-				}
 				if (i < list.size() && list.get(i) == insn) {
 					list.set(i, modInsn);
+				} else {
+					int idx = InsnList.getIndex(list, insn);
+					if (idx == -1) {
+						throw new JadxRuntimeException("Failed to replace insn");
 					}
+					list.set(idx, modInsn);
 				}
 				if (list.size() < insnCount) {
 					// some insns removed => restart block processing
@@ -82,27 +79,15 @@ public class SimplifyVisitor extends AbstractVisitor {
 				}
 			}
 		}
-
-	private static InsnNode simplifyOneArgConsecutive(InsnNode insn1, InsnNode insn2, ArithNode modInsn) {
-		if (insn1.getType() == InsnType.IGET
-				&& insn2.getType() == InsnType.IPUT
-				&& insn1.getResult().getSVar().getUseCount() == 2
-				&& insn2.getArg(1).equals(insn1.getResult())) {
-
-			FieldInfo field = (FieldInfo) ((IndexInsnNode) insn2).getIndex();
-			FieldArg fArg = new FieldArg(field, new InsnWrapArg(insn1));
-			return new ArithNode(modInsn.getOp(), fArg, modInsn.getArg(1));
-		}
-		return null;
 	}
 
-	private static InsnNode simplifyInsn(MethodNode mth, InsnNode insn) {
+	private static InsnNode simplifyInsn(MethodNode mth, BlockNode block, InsnNode insn) {
 		if (insn.contains(AFlag.DONT_GENERATE)) {
 			return null;
 		}
 		for (InsnArg arg : insn.getArguments()) {
 			if (arg.isInsnWrap()) {
-				InsnNode ni = simplifyInsn(mth, ((InsnWrapArg) arg).getWrapInsn());
+				InsnNode ni = simplifyInsn(mth, block, ((InsnWrapArg) arg).getWrapInsn());
 				if (ni != null) {
 					arg.wrapInstruction(ni);
 				}
@@ -124,7 +109,7 @@ public class SimplifyVisitor extends AbstractVisitor {
 
 			case IPUT:
 			case SPUT:
-				return convertFieldArith(mth, insn);
+				return convertFieldArith(mth, block, insn);
 
 			case CHECK_CAST:
 				return processCast(mth, insn);
@@ -421,7 +406,7 @@ public class SimplifyVisitor extends AbstractVisitor {
 	 * Convert field arith operation to arith instruction
 	 * (IPUT = ARITH (IGET, lit) -> ARITH (fieldArg <op>= lit))
 	 */
-	private static InsnNode convertFieldArith(MethodNode mth, InsnNode insn) {
+	private static ArithNode convertFieldArith(MethodNode mth, BlockNode block, InsnNode insn) {
 		InsnArg arg = insn.getArg(0);
 		if (!arg.isInsnWrap()) {
 			return null;
@@ -451,6 +436,7 @@ public class SimplifyVisitor extends AbstractVisitor {
 					return null;
 				}
 			}
+			reg = inlineFieldGet(reg, block, get, insn);
 			FieldArg fArg = new FieldArg(field, reg);
 			if (wrapType == InsnType.ARITH) {
 				ArithNode ar = (ArithNode) wrap;
@@ -467,4 +453,24 @@ public class SimplifyVisitor extends AbstractVisitor {
 		}
 		return null;
 	}
+
+	private static InsnArg inlineFieldGet(@Nullable InsnArg arg, BlockNode block, InsnNode get, InsnNode insn) {
+		if (arg == null || !arg.isRegister()) {
+			return arg;
+		}
+		RegisterArg reg = (RegisterArg) arg;
+		InsnNode assignInsn = reg.getAssignInsn();
+		SSAVar ssaVar = reg.getSVar();
+		if (ssaVar.getUseCount() == 2 && !ssaVar.isUsedInPhi() && assignInsn != null) {
+			List<RegisterArg> useList = ssaVar.getUseList();
+			if (useList.get(0).getParentInsn() == get && useList.get(1).getParentInsn() == insn) {
+				InsnType assignInsnType = assignInsn.getType();
+				if (assignInsnType == InsnType.IGET || assignInsnType == InsnType.SGET) {
+					InsnList.remove(block, assignInsn);
+					return InsnArg.wrapArg(assignInsn);
+				}
+			}
+		}
+		return arg;
+	}
 }