[torque] fix bug in CodeAssemblerParameterizedLabelBase

Bug: v8:7793
Change-Id: I6e1fb19fb260350daca8351321a79d038b5fdbd3
Reviewed-on: https://chromium-review.googlesource.com/c/1436053Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59401}

src/compiler/code-assembler.cc

@@ -1820,6 +1820,8 @@ void CodeAssemblerParameterizedLabelBase::AddInputs(std::vector<Node*> inputs) {
   if (!phi_nodes_.empty()) {
     DCHECK_EQ(inputs.size(), phi_nodes_.size());
     for (size_t i = 0; i < inputs.size(); ++i) {
+      // We use {nullptr} as a sentinel for an uninitialized value.
+      if (phi_nodes_[i] == nullptr) continue;
       state_->raw_assembler_->AppendPhiInput(phi_nodes_[i], inputs[i]);
     }
   } else {

test/torque/test-torque.tq

@@ -413,6 +413,11 @@ namespace test {
     label Exit {
       check(j == 10);
     }
+
+    // Test if we can handle uninitialized values on the stack.
+    let i: Smi;
+    for (let j: Smi = 0; j < 10; ++j) {
+    }
   }
 
   macro TestSubtyping(x: Smi) {