Make control flow analysis of infinite FOR consistent with infinite while loops

An upcoming change in MaybeReachingVariableUse unit tests exposed an issue with FOR loops where `for(i=0; ; i++) {x=1;} foo(x)` would still create an edge (Branch.ON_FALSE) in the CFG from the FOR node to the `foo(x)` node after the block ends.

This behavior is incorrect because, with the Branch.ON_FALSE down edge from FOR to `foo(x)` the MaybeReachingVariableUse pass will consider the foo(x) use reachable to the def `x=1`, when in reality it is not reachable.

Inconsistency:
`for(;;) { x=1;} foo(x);` // considered not reachable use
`for(;true;) { x=1;} foo(x);` // considered reachable use

This CL fixes the above inconsistency.

PiperOrigin-RevId: 322491736

Author: rishipal

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

@@ -450,7 +450,7 @@ private void handleFor(Node forNode) {
     // The edge that transfer control to the beginning of the loop body.
     createEdge(forNode, Branch.ON_TRUE, computeFallThrough(body));
     // The edge to end of the loop.
-    if (!cond.isEmpty()) {
+    if (!cond.isEmpty() && !cond.isTrue()) {
       createEdge(forNode, Branch.ON_FALSE, computeFollowNode(forNode, this));
     }
     // The end of the body will have a unconditional branch to our iter

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

@@ -155,11 +155,10 @@ private static List<DiGraphEdge<Node, Branch>> getAllDownEdges(
   }
 
   /**
-   * Assert that there exists a control flow edge of the given type
-   * from some node with the first token to some node with the second token.
+   * Assert that there exists no control flow edge of the given type from some node with the first
+   * token to some node with the second token.
    */
-  private static void assertNoEdge(ControlFlowGraph<Node> cfg, Token startToken,
-      Token endToken) {
+  private static void assertNoEdge(ControlFlowGraph<Node> cfg, Token startToken, Token endToken) {
     assertThat(getAllEdges(cfg, startToken, endToken)).isEmpty();
   }
 
@@ -310,12 +309,62 @@ public void testSimpleIf() throws IOException {
 
   @Test
   public void testBreakingBlock() throws IOException {
-    // BUG #1382217
     String src = "X: { while(1) { break } }";
     ControlFlowGraph<Node> cfg = createCfg(src);
     assertUpEdge(cfg, Token.BREAK, Token.BLOCK, Branch.UNCOND);
   }
 
+  @Test
+  public void testBreakingWhile() {
+    String src = "var x; while(true) { break; } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.WHILE, Token.BLOCK, Branch.ON_TRUE);
+    assertDownEdge(cfg, Token.BLOCK, Token.BREAK, Branch.UNCOND);
+    assertCrossEdge(cfg, Token.BREAK, Token.EXPR_RESULT, Branch.UNCOND);
+  }
+
+  @Test
+  public void testInifiteLoopWhile() {
+    String src = "var x; while(true) { } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.WHILE, Token.BLOCK, Branch.ON_TRUE);
+    assertNoEdge(cfg, Token.WHILE, Token.EXPR_RESULT);
+  }
+
+  @Test
+  public void testInifiteLoopFor_emptyCond() {
+    String src = "var x; for(;;) { } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.FOR, Token.BLOCK, Branch.ON_TRUE);
+    assertNoEdge(cfg, Token.FOR, Token.EXPR_RESULT);
+  }
+
+  @Test
+  public void testBreakingFor_emptyCond() {
+    String src = "var x; for(;;) { break; } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.FOR, Token.BLOCK, Branch.ON_TRUE);
+    assertDownEdge(cfg, Token.BLOCK, Token.BREAK, Branch.UNCOND);
+    assertCrossEdge(cfg, Token.BREAK, Token.EXPR_RESULT, Branch.UNCOND);
+  }
+
+  @Test
+  public void testInifiteLoopFor_trueCond() {
+    String src = "var x; for(;true;) { } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.FOR, Token.BLOCK, Branch.ON_TRUE);
+    assertNoEdge(cfg, Token.FOR, Token.EXPR_RESULT);
+  }
+
+  @Test
+  public void testBreakingFor_trueCond() {
+    String src = "var x; for(;true;) { break; } x();";
+    ControlFlowGraph<Node> cfg = createCfg(src);
+    assertDownEdge(cfg, Token.FOR, Token.BLOCK, Branch.ON_TRUE);
+    assertDownEdge(cfg, Token.BLOCK, Token.BREAK, Branch.UNCOND);
+    assertCrossEdge(cfg, Token.BREAK, Token.EXPR_RESULT, Branch.UNCOND);
+  }
+
   @Test
   public void testThrowInCatchBlock() throws IOException {
     String src = "try { throw ''; } catch (e) { throw e;} finally {}";