Compute variable liveness for optional chaining

PiperOrigin-RevId: 321821942

Author: rishipal

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

@@ -298,11 +298,22 @@ private void computeGenKill(Node n, BitSet gen, BitSet kill, boolean conditional
       case AND:
       case OR:
       case COALESCE:
+      case OPTCHAIN_GETELEM:
+      case OPTCHAIN_GETPROP:
         computeGenKill(n.getFirstChild(), gen, kill, conditional);
         // May short circuit.
         computeGenKill(n.getLastChild(), gen, kill, true);
         return;
 
+      case OPTCHAIN_CALL:
+        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()) {
+          computeGenKill(c, gen, kill, true);
+        }
+        return;
+
       case HOOK:
         computeGenKill(n.getFirstChild(), gen, kill, conditional);
         // Assume both sides are conditional.

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

@@ -109,13 +109,57 @@ public void nullishCoalesce() {
     assertLiveBeforeX("var a,b;X:if(b??a) {}", "a");
     assertLiveBeforeX("var a,b;X:if(b??b(a)) {}", "a");
 
-    // The kill can be "conditional" due to short circuit.
+    // Unconditionally killed on lhs of ??
     assertNotLiveAfterX("var a,b;X:a();if((a=b)??b){}a()", "a");
     assertNotLiveAfterX("var a,b;X:a();while((a=b)??b){}a()", "a");
-    assertLiveBeforeX("var a,b;a();X:if(b??(a=b)){}a()", "a"); // Assumed live.
-    assertLiveBeforeX("var a,b;a();X:if(a??(a=b)){}a()", "a");
-    assertLiveBeforeX("var a,b;a();X:while(b??(a=b)){}a()", "a");
-    assertLiveBeforeX("var a,b;a();X:while(a??(a=b)){}a()", "a");
+
+    // The kill can be "conditional" due to short circuit.
+    assertLiveBeforeX("var a,b; X:if(b??(a=b)){}a()", "a"); // Assumed live.
+    assertLiveBeforeX("var a,b; X:if(a??(a=b)){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(b??(a=b)){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(a??(a=b)){}a()", "a");
+  }
+
+  @Test
+  public void optionalChainingGetProp() {
+    // Reading the var on lhs of opt chain makes the variable live.
+    assertNotLiveBeforeX("var a,b; X:if(b) {}", "a");
+    assertLiveBeforeX("var a,b; X:if(a?.b) {}", "a");
+
+    // Reading a prop with the same name as var does not make the var live
+    assertNotLiveBeforeX("var a,b;X:if(b?.a) {}", "a");
+
+    // unconditional kill on lhs of ?.
+    assertNotLiveAfterX("var a,b;X:a();if((a=c)?.b){} a()", "a");
+    assertNotLiveAfterX("var a,b;X:a();while((a=b)?.b){} a()", "a");
+  }
+
+  @Test
+  public void optionalChainingCall() {
+    // conditionally accessing var keeps it live
+    assertLiveBeforeX("var a,b; X:if(b?.(a)){}", "a");
+    // conditionally overwriting var does not kill it
+    assertLiveBeforeX("var a,b; X:if(b?.(a=c)){} a();", "a");
+
+    // conditional overwrite on rhs of ?. does not kill the var
+    assertLiveBeforeX("var a,b; X:if(b?.(a=b)){}a()", "a"); // Assumed live.
+    assertLiveBeforeX("var a,b; X:if(a?.(a=b)){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(b?.(a=b)){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(a?.(a=b)){}a()", "a");
+  }
+
+  @Test
+  public void optionalChainingGetElem() {
+    // conditionally accessing var keeps it live
+    assertLiveBeforeX("var a,b; X:if(b?.[a]) {}", "a");
+    // conditionally overwriting var does not kill it
+    assertLiveBeforeX("var a,b; X:if(b?.[a=c]) {} a();", "a");
+
+    // conditional overwrite on rhs of ?. does not kill the var
+    assertLiveBeforeX("var a,b; X:if(b?.[a=b]){}a()", "a"); // Assumed live.
+    assertLiveBeforeX("var a,b; X:if(a?.[a=b]){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(b?.[a=b]){}a()", "a");
+    assertLiveBeforeX("var a,b; X:while(a?.[a=b]){}a()", "a");
   }
 
   @Test