Fix a bug in calculating liveness for OPTCHAIN_CALL nodes

PiperOrigin-RevId: 321882231

Author: rishipal

src/com/google/javascript/jscomp/LiveVariablesAnalysis.java

@@ -309,7 +309,7 @@ private void computeGenKill(Node n, BitSet gen, BitSet kill, boolean conditional
         computeGenKill(n.getFirstChild(), gen, kill, conditional);
         // Unlike OPTCHAIN_GETPROP and OPTCHAIN_GETELEM, the OPTCHAIN_CALLs can have multiple
         // children on rhs which get executed conditionally
-        for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
+        for (Node c = n.getSecondChild(); c != null; c = c.getNext()) {
           computeGenKill(c, gen, kill, true);
         }
         return;

test/com/google/javascript/jscomp/LiveVariablesAnalysisTest.java

@@ -138,6 +138,10 @@ public void optionalChainingGetProp() {
   public void optionalChainingCall() {
     // conditionally accessing var keeps it live
     assertLiveBeforeX("var a,b; X:if(b?.(a)){}", "a");
+
+    // unconditionally overwriting a var kills it
+    assertNotLiveAfterX("var a,b; X:a(); if((a=b)?.b()){} a()", "a");
+
     // conditionally overwriting var does not kill it
     assertLiveBeforeX("var a,b; X:if(b?.(a=c)){} a();", "a");
 
@@ -152,6 +156,10 @@ public void optionalChainingCall() {
   public void optionalChainingGetElem() {
     // conditionally accessing var keeps it live
     assertLiveBeforeX("var a,b; X:if(b?.[a]) {}", "a");
+
+    // unconditionally overwriting a var kills it
+    assertNotLiveAfterX("var a,b; X:a(); if((a=b)?.[b]){} a()", "a");
+
     // conditionally overwriting var does not kill it
     assertLiveBeforeX("var a,b; X:if(b?.[a=c]) {} a();", "a");