Diagnose on using uninitialized `out` param. (#2803)

* Diagnose on using uninitialized `out` param.

* Hack to allow `out Vertices<T>`.

* Fix.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/source/slang/slang-ir-reachability.cpp b/source/slang/slang-ir-reachability.cpp
new file mode 100644
index 000000000..9d36b9450
--- /dev/null
+++ b/source/slang/slang-ir-reachability.cpp
@@ -0,0 +1,39 @@
+#include "slang-ir-reachability.h"
+
+namespace Slang
+{
+// Computes whether block1 can reach block2.
+// A block is considered not reachable from itself unless there is a backedge in the CFG.
+
+bool ReachabilityContext::computeReachability(IRBlock* block1, IRBlock* block2)
+{
+    workList.clear();
+    reachableBlocks.Clear();
+    workList.add(block1);
+    for (Index i = 0; i < workList.getCount(); i++)
+    {
+        auto src = workList[i];
+        for (auto successor : src->getSuccessors())
+        {
+            if (successor == block2)
+                return true;
+            if (reachableBlocks.Add(successor))
+                workList.add(successor);
+        }
+    }
+    return false;
+}
+
+bool ReachabilityContext::isBlockReachable(IRBlock* from, IRBlock* to)
+{
+    BlockPair pair;
+    pair.first = from;
+    pair.second = to;
+    bool result = false;
+    if (reachabilityResults.TryGetValue(pair, result))
+        return result;
+    result = computeReachability(from, to);
+    reachabilityResults[pair] = result;
+    return result;
+}
+}