fix: collapse ternary with the same constant in both branches

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

@@ -138,8 +138,7 @@ private InsnNode simplifyInsn(MethodNode mth, InsnNode insn, @Nullable InsnNode
 				simplifyIf(mth, (IfNode) insn);
 				break;
 			case TERNARY:
-				simplifyTernary(mth, (TernaryInsn) insn);
-				break;
+				return simplifyTernary(mth, (TernaryInsn) insn);
 
 			case INVOKE:
 				return convertInvoke(mth, (InvokeNode) insn);
@@ -306,13 +305,58 @@ private static void simplifyIf(MethodNode mth, IfNode insn) {
 	/**
 	 * Simplify condition in ternary operation
 	 */
-	private static void simplifyTernary(MethodNode mth, TernaryInsn insn) {
+	private static InsnNode simplifyTernary(MethodNode mth, TernaryInsn insn) {
+		if (insn.getArg(0).isSameConst(insn.getArg(1)) && canDropCondition(insn.getCondition())) {
+			// both branches yield the same constant and the condition has no side effect: 'c ? x : x' => 'x'
+			for (RegisterArg reg : insn.getCondition().getRegisterArgs()) {
+				InsnRemover.unbindArgUsage(mth, reg);
+			}
+			InsnArg valueArg = insn.getArg(0);
+			InsnNode value;
+			if (valueArg.isInsnWrap()) {
+				value = ((InsnWrapArg) valueArg).getWrapInsn().copyWithoutResult();
+			} else {
+				value = new InsnNode(InsnType.CONST, 1);
+				value.addArg(valueArg);
+			}
+			value.setResult(insn.getResult());
+			value.copyAttributesFrom(insn);
+			return value;
+		}
 		IfCondition condition = insn.getCondition();
 		if (condition.isCompare()) {
 			simplifyIf(mth, condition.getCompare().getInsn());
 		} else {
 			insn.simplifyCondition();
 		}
+		return null;
+	}
+
+	/**
+	 * A condition can be dropped only if evaluating it has no observable effect. Every condition
+	 * instruction must be in {@link InsnNode#canThrowException()}'s no-throw set (which holds only
+	 * pure insns: const/compare/move/neg), and every operand must be a parameter or a plain field
+	 * read. Anything else (a cast, invoke, array access, ...) may be the last use of a value whose
+	 * removal drops a cast/exception (e.g. the erased CHECK_CAST behind 'String s = list.get(0)').
+	 */
+	private static boolean canDropCondition(IfCondition condition) {
+		boolean[] pure = { true };
+		condition.visitInsns(insn -> {
+			if (insn.canThrowException()) {
+				pure[0] = false;
+			}
+		});
+		if (!pure[0]) {
+			return false;
+		}
+		for (RegisterArg reg : condition.getRegisterArgs()) {
+			// null assign == method argument (no producing insn to drop)
+			InsnNode assign = reg.getSVar().getAssignInsn();
+			if (assign != null && assign.getType() != InsnType.IGET && assign.getType() != InsnType.SGET) {
+				return false;
+			}
+		}
+		return true;
 	}
 
 	/**

jadx-core/src/test/java/jadx/tests/integration/conditions/TestTernarySameResult.java

@@ -0,0 +1,31 @@
+package jadx.tests.integration.conditions;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.tests.api.RaungTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestTernarySameResult extends RaungTest {
+
+	// Uses hand-written bytecode: javac folds 'if (c) return x; else return x;', so a plain Java
+	// test can't produce the degenerate 'c ? x : x' ternary that this fix collapses.
+
+	@Test
+	public void test() {
+		assertThat(getClassNodeFromRaung())
+				.code()
+				// same constant in both branches + side-effect-free condition => collapse
+				.doesNotContain("? null : null")
+				.doesNotContain("? 7 : 7")
+				.doesNotContain("? \"x\" : \"x\"")
+				.containsOne("return null;")
+				.containsOne("return 7;")
+				.containsOne("return \"x\";")
+				// must keep the ternary: different values, a side effect in the condition,
+				// or an operand whose cast would be dropped with the condition
+				.containsOne("z ? 7 : 8")
+				.containsOne("? 5 : 5")
+				.containsOne("? 9 : 9");
+	}
+}

jadx-core/src/test/raung/conditions/TestTernarySameResult.raung

@@ -0,0 +1,194 @@
+.version 65  # Java 21
+.class public super conditions/TestTernarySameResult
+.source "TestTernarySameResult.java"
+
+.field private calls I
+
+.method public <init>()V
+    .max stack 1
+    .max locals 1
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .line 2
+    aload 0
+    invokespecial java/lang/Object <init> ()V
+    return
+.end method
+
+.method public retNull(Ljava/lang/Object;)Ljava/lang/Object;
+    .max stack 1
+    .max locals 2
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "o" Ljava/lang/Object;
+    .line 5
+    aload 1
+    ifnonnull :L1
+    aconst_null
+    areturn
+  :L1
+    .stack same
+    aconst_null
+    areturn
+.end method
+
+.method public retSame(Z)I
+    .max stack 1
+    .max locals 2
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "z" Z
+    .line 8
+    iload 1
+    ifeq :L1
+    bipush 7
+    ireturn
+  :L1
+    .stack same
+    bipush 7
+    ireturn
+.end method
+
+.method public retStr(Z)Ljava/lang/String;
+    .max stack 1
+    .max locals 2
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "z" Z
+    .line 11
+    iload 1
+    ifeq :L1
+    ldc "x"
+    areturn
+  :L1
+    .stack same
+    ldc "x"
+    areturn
+.end method
+
+.method public assignSame(Z)I
+    .max stack 1
+    .max locals 3
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "z" Z
+    .line 15
+    iload 1
+    ifeq :L1
+    bipush 7
+    istore 2
+    .local 2 "r" I
+    goto :L3
+  :L1
+    .stack same
+    .end local 2 # "r"
+    bipush 7
+    istore 2
+  :L3
+    .local 2 "r" I
+    .line 16
+    .stack append
+        int
+    .end stack
+    iload 2
+    ireturn
+.end method
+
+.method public keepDiff(Z)I
+    .max stack 1
+    .max locals 3
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "z" Z
+    .line 20
+    iload 1
+    ifeq :L1
+    bipush 7
+    istore 2
+    .local 2 "r" I
+    goto :L3
+  :L1
+    .stack same
+    .end local 2 # "r"
+    bipush 8
+    istore 2
+  :L3
+    .local 2 "r" I
+    .line 21
+    .stack append
+        int
+    .end stack
+    iload 2
+    ireturn
+.end method
+
+.method public keepEffect()I
+    .max stack 1
+    .max locals 2
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .line 25
+    aload 0
+    invokevirtual conditions/TestTernarySameResult ping ()I
+    ifle :L1
+    iconst_5
+    istore 1
+    .local 1 "r" I
+    goto :L3
+  :L1
+    .stack same
+    .end local 1 # "r"
+    iconst_5
+    istore 1
+  :L3
+    .local 1 "r" I
+    .line 26
+    .stack append
+        int
+    .end stack
+    iload 1
+    ireturn
+.end method
+
+.method public keepCast(Ljava/lang/Object;)I
+    .max stack 1
+    .max locals 3
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .local 1 "o" Ljava/lang/Object;
+    .line 29
+    aload 1
+    checkcast java/lang/Integer
+    astore 2
+    .local 2 "i" Ljava/lang/Integer;
+    .line 30
+    aload 2
+    ifnull :L2
+    bipush 9
+    goto :L3
+  :L2
+    .stack append
+        java/lang/Integer
+    .end stack
+    bipush 9
+  :L3
+    .stack same1 int
+    ireturn
+.end method
+
+.method private ping()I
+    .max stack 3
+    .max locals 1
+
+    .local 0 "this" Lconditions/TestTernarySameResult;
+    .line 32
+    aload 0
+    dup
+    getfield conditions/TestTernarySameResult calls I
+    iconst_1
+    iadd
+    putfield conditions/TestTernarySameResult calls I
+    aload 0
+    getfield conditions/TestTernarySameResult calls I
+    ireturn
+.end method